MIAMI UNIVERSITY the Graduate School Certificate for Approving The

MIAMI UNIVERSITY

The Graduate School

Certificate for Approving the Dissertation

We hereby approve the Dissertation

Philias Daka

Candidate for the Degree:

Doctor of Philosophy

______

Hong Wang, Advisor

______

Michael Novak, Committee Chair

______

Scot Hartley, Reader

______

Jonathan Scaffidi, Reader

______John Rakovan, Graduate School Representative

ABSTRACT ENAMINE-METAL LEWIS ACID BIFUNCTIONAL CATALYSTS FOR ASYMMETRIC ALDOL REACTIONS. DESIGN AND SYNTHESIS OF STAT3 INHIBITORS. by Philias Daka This dissertation comprises two parts: Part I focuses on enamine-metal-Lewis-acid bifunctional catalysts. An introduction on the different methods of acquiring enantiomeric rich compounds is given, followed by an in depth discussion of organocatalysts and bifunctional catalysts. Some examples of metal catalysts and organocatalysts are also discussed. With the intent of bridging the gap between the traditional metal catalysis and the prosperous organocatalysis, enamine-metal-Lewis-acid bifunctional catalysts were developed. Even though there are examples in the literature of combining transition metal catalysis with enamine catalysis to carry out asymmetric synthesis, the limitation is the un-compromisable requirement of soft-hard combination to avoid catalyst self-quenching. Here, we solve this problem by carefully designing ligands that possess a Lewis base and at the same time can ‘trap’ the Lewis acid, thereby incorporating the base and the acid in the same molecule. Other properties such as rigidity, the distance between the acid and the base, and the strength of the metal Lewis acids can be fine-tuned at will. Tetra-, tri-, and bidentate ligand systems were designed. These different ligands were tethered to chiral primary or secondary amines as the Lewis bases. The catalysts were employed in direct asymmetric aldol reactions of aldehydes and ketones, giving good to excellent results in terms of yield and enantioselectivity with as low as 1mol% of catalyst loading. The investigation was further extended to ketone–ketone condensation of both inactivated and activated acceptors, with poor results. Part II describes the design and synthesis of organic small molecule inhibitors targeting the protein signal transducer and activator of transcription 3 (STAT3). Because STAT3 plays a crucial role in cell proliferation, designing small molecules that can inhibit its function can be a way to combat tumors. A number of STAT3 inhibitors have been developed thus far by other groups; however, very few have reached clinical trials. An inhibitor developed in our group, e.g. (XZH- 5(166a) was found to inhibit STAT3 with appreciable IC50 value of 30µM in liver cancer cell lines. With this initial promising result, we designed and synthesized 15 166a derivatives in order to study the structural activity relationships (SARs). IC50 values of as low as 8.8µM in liver cancer cell lines have been achieved with these inhibitors.

ENAMINE-METAL LEWIS ACID BIFUNCTIONAL CATALYSTS FOR ASYMMETRIC ALDOL REACTIONS. DESIGN AND SYNTHESIS OF STAT3 INHIBITORS.

A DISSERTATION

Submitted to the Faculty of

Miami University in Partial

Fulfillment of the requirements

For the degree of

Doctor of Philosophy

Department of Chemistry and Biochemistry

Philias Daka

Miami University

Oxford, Ohio

2013

Dissertation Director: Dr. Hong Wang

Table of Contents Chapter I. Significance of enantiopure compounds………………………………...1 Research goals……………………………………………………………………...1 1.0: Ways of acquiring chiral compounds………………………………………….2 1.1: Resolution …………………………………………………………………...... 2 1.2: Chiral pool…………………………………………………………………...... 3 1.3: Chiral auxiliary………………………………………………………………...3 1.4: Dynamic and kinetic resolution..……………………………………………....3 1.5: Asymmetric catalysis…………………………………………………………..4 1.5.1: Biocatalysis…………………………………………………………………..4 1.5.2: Chiral metal complexes………………………………………………….…..5 1.5.3: Organocatalysis…………………………………………...…………………7 1.5.3.1: Chiral Lewis base/acid catalysis………………………………………...…7 1.5.3.2: Chiral Brønted acid catalysis……………………………………………..12 1.6: Bifunctonal catalysts…………….…………………………………..……….15 1.6.1: Cinchona alkaloids as bifunctional catalysts…………………………….…16 1.6.2: Chiral cyclohexane-diamine based bifunctional catalysts……….…………20 1.6.3: Chiral binaphthyl-based amine catalysts…………………………………...22 1.6.4: Proline and its derivatives………………………………………….……....23 1.7: Combining transition metal catalysis and organocatalysis………….………..25 1.7.1: Enamine-transition metal cooperative catalysis……………………………25 1.7.2: Metal catalysis and chiral Brønsted acid counter anion……………………29 1.8: Enamine-metal Lewis acid bifunctional catalysts……...…………………….32 1.8.0: Introduction………………………………………………………………...32

1.8.1: Catalysts based on tetradentate secondary amine ligand system: 6, 6’– diamino-2,2’-bipyridine (Dadp) (105)…………………………………….……....36

1.8.1.1: Synthesis of 6,6’–diamino-2,2’bipyridine( Dadp) (107)…………....……38 1.8.1.2a: Attempted synthesis of (2R,2'S)-N,N'-([2,2'-bipyridine]-6,6'-diyl)bis(1- methylpyrrolidine-2-carboxamide) (105)…………………………………………39 1.8.1.2b: Attempted synthesis of (2R,2'S)-N,N'-([2,2'-bipyridine]-6,6'-diyl)bis(1- methylpyrrolidine-2-carboxamide) (105)…………………………………………40 1.8.2: Catalysts based on tridentate secondary amine ligand system………...... 46 1.8.3: Catalysts based on tridentate primary amine ligand system………….…….51 1.8.4: Catalysts based on bidentate primary amine ligand system………………..58 1.8.5: Catalysts based on bidentate secondary amine ligand system: metal–Lewis acid promoted highly stereoselective formation of cyclic aminals……………….72 1.8.6: Direct asymmetric aldol reaction of ketones……………………………….84 1.8.6.1: Direct asymmetric aldol reactions to un-activated ketones………………85 1.8.6.2: Direct asymmetric aldol reactions to activated ketones………….………91 1.8.6.2.1: Direct asymmetric aldol condensation of isatin and acetone..….……...92 1.8.6.2.2: Direct asymmetric aldol condensation of isatin and (E)-4-phenylbut-3- en-2-one……………………………………………………………………….…..95 Experimental for Part I………………………………………………………..…105 References for Part I….………………………………………………………….137 Chapter II Design and synthesis of STAT3 inhibitors…………………………..156 2.0: Introduction…………………………………………………………………156 2.1: Design of the inhibitors…………………………………………………...... 162 Experimental for Part II………………………………………………………….170 References for Part II…………………………………………………………….181 Spectra…………………………………………………………………………...184

iii

List of Tables Table 1.8.1.1a.1: Coupling reagents used for ligand 105…………………………39 Table 1.8.1.1a.2: Metal screening………………………………………………....41

Table 1.8.1.1b.3: Solvent screening with Co(ClO4)2...... 43

Table 1.8.1.1b.4: Solvents screening with Cu(SbF6)2………….…………………44 Table 1.8.2.5: Aldehyde scope for the direct asymmetric aldol reaction....………48 Table 1.8.2.6: Aldehyde scope with ligand 123…………………………….…….50 Table 1.8.3.7: Aldehyde scope with ligand 130c……………………………...….55 Table 1.8.3.8: Aldehyde scope with other cyclic ketones………………….……..57 Table 1.8.4.9: Metal screening of the reaction between cyclohexanone and 4- nitrobenzaldehyde using weak Lewis acids……………………………………….59 Table 1.8.4.10: Metal screening of the reaction between cyclohexanone and 4- nitrobenzaldehyde using stronger Lewis acids……………………………………61

Table 1.8.4.11: Solvent screening using La(OTf)3/139a………………………….62

Table 1.8.4.12: Ligand screening with Cu(SbF6)2…………………………...……63 Table 1.8.4.13: Investigation of the metal to ligand ratio…………………………65

Table 1.8.4.14: Solvent screening Cu(SbF6)2/139a……………………………….66

Table 1.8.4.15: Aldehyde scope with cyclohexanone using 139a/ Cu(SbF6)2.…...67

Table 1.8.4.16: Aldehyde scope with cyclohexanone139g/ Cu(SbF6)2…….……..68 Table 1.8.4.17: Investigating catalyst loading………………………….…………69 Table 1.8.4.18: Investigating water tolerance of the catalyst…………………...... 70 Table 1.8.5.19: Screening of metals with 140………………………………….…73

Table 1.8.5.20: Solvent screening with 140/Zn(OAc)2…………………………...74 Table 1.8.5.21: Metal screening in the formation of cyclic aminals……………...79 Table 1.8.5.22: Aldehyde scope with substrate 140……………………………....80

Table 1.8.5.23: Aldehyde scope with (S)-N-phenylpyrrolidine-2-carboxamide (148)……………………………………………………………………………….81 Table 1.8.6.1.24: Metal screening for self aldol reaction of cyclohexanone…...... 86 Table 1.8.6.1.25: Solvent screening for self aldol reaction of cyclohexanone…....87 Table 1.8.6.1.26: Exploration of the cross aldol reaction of inactivated ketones…………………………………………………………………………….89 Table 1.8.5.2.27: Exploration of the crossed aldol condensation with activated ketones……………………………………………………………….……….…...91 Table 1.8.6.2.1.28: Metal screening of the indole reaction between isatin and acetone…………………………………………………………………………….93 Table 1.8.6.2.2.29: Solvent screening for HDA reaction………………………....96 Table 1.8.6.2.2.30: Investigation of ligands and other conditions………………...98 Table 1.8.6.2.2.31: Screening of more conditions using ligand 161…………….100 Table 1.8.6.2.2.32: Investigation of the stoichiometry of the HDA reaction……101

Table 2.1.33: IC50 values for different cancer cell lines………………………....166

List of Figures

Figure 1.5.2.1: Chiral ligands……………….…………………………...…………6 Figure 1.5.3.2: Modes of activation of organocatalysts …………………………...7 Figure 1.5.3.1.3: Iminium and enamine catalytic cycles…………………………...9 Figure 1.5.3.2.4: Specific and general acid catalysis………………….…………..12 Figure 1.5.3.2.5: Neutral Brønsted acids catalysts………………………………..13 Figure 1.5.3.2.6: Brønsted acid catalyst examples………………...……………...14 Figure 1.6.1.7: Cinchona alkaloids bifunctonal catalyst examples.….…………...16 Figure 1.6.2.8: Cyclohexane-diamine catalyst……………………………………20 Figure 1.7.2.9: Interaction of the nucleophile and electrophile catalyzed by counter ion catalyst………………………………………………………………………...30 Figure 1.8.0.10: Illustration of: (a) Enamine-metal Lewis acid bifunctional catalyst (b) advantages of our bifunctional catalysts …….………………………….…….33

Figure 1.8.0.11: Crystal structure of Cu(II) (A)2(ONO2)2……..…………….……35 Figure 1.8.1.12: Tetradentate ligand and the metal trapped by the ligand………..36 Figure 1.8.3.13: Tridentate primary amine ligands……………….………………54 Figure 18.4.14: Bidentate primary amine ligands..……………………….………58 Figure 1.8.4.15: Proposed transitional state showing a Re face attack…...... 71 Figure 1.8.5.16: 1HNMR of the reaction mixture for the cyclization reaction. top: with Cu(NO3)2; bottom: without metal……………………………………………76 Figure 1.8.5.17: Elucidation of the trans- product………………………………..77 Figure 1.8.6.2.1.18: Ligand systems used in the aldol reaction of acetone and isatin……………………………………………………………………………….92 Figure 1.8.6.2.2.19: X-ray crystal structure of the 5-nitro-isatin and (E)-4- phenylbut-3-en-2-one adduct……...……………….…………………………….102 Figure 2.0.20: STAT3 structure……………………….………………………....156 vi

Figure 2.0.21: Showing different processes that STAT3 undergoes before it initiates transcription……..……………………………………………………...159 Figure 2.0.22: Examples of peptidomimics inhibitors of STAT3……………….160 Figure 2.0.23: Examples of non–peptidomimics inhibitors of STAT3…..…....160 Figure 2.1.24: SH2 binding pockets 1, 2 and 3 (circles) of STAT3 and the binding between 166a and STAT3 SH2………………………………………………….162 Figure 2.1.25: Computer model of 166a interaction with STAT3………………163 Figure 2.1.26: Inhibitors synthesized…………………………………….……...165 Figure 2.1.27: Showing the three parts that we focused during SARs…...……...167

vii

List of Schemes Scheme1.5.1.1: Use of enzymes as chiral catalyst………………………………....5 Scheme 1.5.2.2: Use of metal complex to synthesize L-DOPA………………...... 6 Scheme 1.5.3.1.3: Intermolecular aldol reaction between acetone and aldehydes…8 Scheme 1.5.3.1.4: Enamine/imminium ion formation……………………………...8 Scheme 1.5.3.1.5: Reaction between organosilanes and aldehydes………………11 Scheme 1.5.3.1.6: Michael addition using trityl perchlorate as catalyst………….11 Scheme 1.5.3.2.7: Activation by hydrogen bonding……………………………...13 Scheme 1.5.3.2.8: Use of BINOL in MBH reaction……………………….…..….14 Scheme 1.5.3.2.9: Use of Brønsted acids to get enantiopure product…………….15 Scheme 1.6.1.10: Use of cincholidine as bifunctional catalyst……..…………….17 Scheme 1.6.1.11: Use of quinidine as bifunctional catalyst…………...... 17 Scheme 1.6.1.12: Use of quinine as bifunctional catalyst…………..…………….18 Scheme 1.6.1.13: Thiourea and cincholine derived catalyst……………………...19 Scheme 1.6.1.14: Michael-aldol reaction using thiourea cincholine derived catalyst…...... 19 Scheme 1.6.2.15: Use of cyclohexane-diamine as bifunctional catalyst……….....21 Scheme 1.6.3.16: Use of chiral binaphthyl-based amine catalysts………………..22 Scheme 1.6.3.17: Use of chiral binaphthyl-based amine catalysts in MBH reaction………………………………………………………………………...... 23 1.6.3.18: Use of chiral binaphthyl-based amine with a thiourea as catalysts MBH………………………………………………………………………………23 1.6.4.19: Proline catalyzed Robinson annulation…………………………..……..24 Scheme 1.6.4.20: Proline catalyzed aldol reaction ………………………….……24 Scheme 1.7.1.21: Combining enamine and transition metal in alkylation……...... 26

viii

Scheme 1.7.1.22: A domino reaction involving an enamine and a transition metal………………………………………………………………………………27 Scheme 1.7.1.23: Enamine–SOMO activation transformation……………..…….28 Scheme 1.7.1.24: A cascade reaction involving enamine-SOMO activation…..…29 Scheme 1.7.2.25: Use of counter ion strategy in a transformation………..………30 Scheme 1.7.2.26: Use of the counter ion method to synthesize a (+) cuperane…..31 Scheme 1.8.0.27: Synthesis of 6, 6'-bis(phenyl-acetamide)-2,2'-bipyridine Metal complex…………………………………………………………………………...34 Scheme 1.8.1.28: Retro synthesis of 105………………………..……………...…37 Scheme 1.8.1.29: Synthesis of 2, 2'–diaminodipyridine…….…...... 38 Scheme 1.8.1.30: Synthesis of N-methylproline……………………...... 38 Scheme 1.8.1.1a.31: Synthesis of Boc proline………………………….….……..40 Scheme 1.8.1.1b.32: Attempted synthesis of 105..………………………..………40 Scheme 1.8.1.1b.33: Synthesis of 120..………….……………...……………..….45 Scheme 1.8.2.34: Synthesis of ligand 122..…………………………………….…46 Scheme 1.8.2.35: Synthesis of ligand 123 and 124………………….……………47 Scheme 1.8.2.36: Reaction between 4-nitrobenzaldehyde and 2-butanone…...….49 Scheme 1.8.3.37: Synthesis of different tridentate ligands…………...…….…….52 Scheme 1.8.3.38: Synthesis of tridentate ligand 131...... ………….……………....52 Scheme 1.8.3.39: Synthesis of tridentate ligand 134..……………….……………53 Scheme 1.8.4.40: General synthesis of bidentate ligands………………………....59 Scheme 1.8.5.41: General synthesis of bidentate secondary amine ligands………72 Scheme 1.8.5.42: Aldol reaction between acetone and 4-nitrobenzaldehyde giving the expected aldol product 118a and the unexpected cyclic aminal 144..….……..75 Scheme 1.8.6.1.43: Self condensation of cyclohexanone……..…………..………85

Scheme 1.8.6.1.44: Crossed aldol reaction between acetophenone and cyclohexanone...... 88 Scheme 1.8.6.1.45: Crossed aldol reaction between acetone and cyclohexanone..88 Scheme 1.8.6.2.2.46: Condensation of isatin and unsaturated ketone…………….95 Scheme 1.8.6.2.2.47: General synthesis of ligands….……..…………….…….…97 Scheme 1.8.6.2.2.48: Synthesis of protected isatin……………..……….………103 Scheme 1.8.6.2.2.49: Attempted cyclization of the aldol product to HDA product………………………………………………………………………..….104 Scheme 2.1.50: General synthesis of inhibitors………………………………....164

Abbreviations

ACDC: Asymmetric counter-anion directed catalysis BINAP: 2, 2’Bis(diphenylphoshino)-1,1’–binaphthyl BOP:(Benzotriazol-1-yloxy)tris(dimethylamino)phosphonium hexafluorophosphate BINOL: 1, 1’–Bi-2- naphthol Boc: t-Butyloxylcarbonyl Bn: Benzyl CAN: Ceric ammonium nitrate Cbz: Carbobenzyloxyl CPME: Cyclopentyl methyl ether CPTKs: Cystosolic protein –tyrosine kinases Dabp: 6,6’–Diamino-2, 2’-bipyridine DCC: Dicyclohexyl carbodiimide DCM: Dichloromethane DIPEA N-Diisopropylethylamine DKR: Dynamic kinetic resolution DMF: N, N-dimethylformamide DMSO: Dimethylsulfoxide DNA: Deoxyribonucleic acid HOMO: Highest occupied molecular orbital HOBt: N-Hydroxybenzotriazole HFIP: Hexafluoroisopropanol HDA: Hetero Diels-Alder HPLC: High performance liquid chromatography

JAK: Janus kinases L-DOPA: L-3,4 Dihydroxyphenylalanine LUMO: Lowest unoccupied molecular orbital MBH: Morrita Haylis Bayman Ms: Molecular sieves MS: Mass spectroscopy MTBE: Methyl tert-butyl ether MVK: Methyl vinyl ketone NMR: Nuclear magnetic resonance NOE: Nuclear overhauser effect NOESY: Nuclear overhauser effect spectroscopy NTs: N–Tosylate PSKs: Protein-bound polysaccharides K PTSA: p-Toluene sulfonic acid PyBOX: Pyridine bisoxazoline SOMO: Single-electron occupied molecular orbital STAT3: Signal transducer activator of transcription 3 TADDOL: α,α,α’ α’–Tetra aryl -1, 3- dioxolan-4 , 5-dimetanol t-bu: tert-butyl TEA: Triethylamine TFA: Trifluoroacetic acid THF: Tetrahydrofuran TIRP: [3,3’–bis (2,4,6-triisopropylphenyl)-1,1’–binaphthyl -2,2’–diyl hydrogen phosphate] TLC: Thin layer chromatography Tol Toluene

xii

DEDICATED

TO MY MOTHER

TISIYENJI BLANDINA NG’WENYA

……it is a shame that she could not see this….

….at least she tried.

xiii

Acknowledgements

My unconditional thanks go to my research advisor Dr. Hong Wang for all the generous support that she has given me during the entire PhD study. She has been instrumental in reminding me the right questions of why and how? that are fundamental to problem solving.

Special thanks go to Dr. Zhenghu Xu who was always next to me when I needed him even to answer even the silliest questions.

Many thanks go to my dissertation committee members: Professor Michael Novak, Dr. Scott Hartley, Dr. Jonathan Scaffidi and Dr. John Rakovan for their time, patience and valuable contribution to this dissertation.

I am also grateful to my research group members Dr. Lu Liu, Lin Jiang, Yongming Deng, Alex Alexa, Nate Carman and Alex Matus for their support during my studies.

I would also want to thank Professor Michael Novak in a special way for sharing their HPLC with us on which most if not all of the data were collected from. And more also for being our technician whenever we broke the instrument.

Special thanks go to the department of Chemistry and Biochemistry and Miami University Ohio at large for giving me the opportunity to learn and meet all the good people.

Last but not least my gratitude goes to my beautiful wife Estele Tembo, my sons Wongani Daka and Thabalala Daka, my adorable daughter Tisiyenji Blandina Daka, for their patience and love.

xiv

Introduction Significance of enantiopure compounds The importance that mother nature places on chirality (handedness) has led to an increase in the demand for chiral materials with different complexity in disciplines such as biological science1, materials science2,3 and the pharmaceutical industry.4-8 This is not surprising because all living organisms consist of chiral biomolecules such as amino acids, nucleic acids, DNA, and sugars. Usually only one form of these biomolecules exist naturally and not the other. For example, only L amino acids and the D sugars occur naturally. Because living organisms are exceptionally chiral, different drug enantiomers usually interact differently with living cells exhibiting different pharmacokinetics and pharmacodynamics resulting in different effects on the organism. One enantiomer can be a good drug while the other can be a poison, as the case was with the Thalidomide tragedy.9 The foundation to the quest of chiral compounds was laid by the detailed elucidation and understanding of optical activity and isomerism.10

Research goals The ultimate goal of our research group is to design enamine-metal Lewis acid bifunctional catalysts based on amino acids and small molecules. With the new catalysts, we should be able to expand the already existing peptide-based catalyst repertoire that has the disadvantage of relying on weak hydrogen bond activation. This will allow us to explore new reactions that can be catalyzed by amino acids. Because we are combining two well established categories of organocatalysis and metal catalysis we should, in principle (because of the unique activation mode of our systems), be able to carry out reactions that are almost unattainable by either 1

organo catalysts or metal catalysts on their own. This will allow us to open a new door in catalysis. We also have the objective of developing STAT3 inhibitors derived from amino acids. This is a very attractive area because up to date this arena has remained untapped in the development of drugs for fighting cancer. Since our starting materials are readily available and non-toxic, synthesis and manipulation of the inhibitors is anticipated to be easy and unlikely to suffer drug attrition.

1.0 Ways of acquiring chiral compounds There are different protocols that are utilized to obtain enantiopure compounds and these methods have become more complex and efficient with time. The choice of the method to use depends on the inherent properties of the particular compound to be separated, how enantiopure you want the product to be, and the ease of the method. Some of the methods are discussed below:

1.1 Resolution In resolution, a racemate can be separated by one of the following methods: recrystallization11, derivatization,12 enzymes,13 and chiral chromatography.14-16

In recrystallization, the racemic compound is recrystallized and the enantiomers are separated by physical means or use of chiral nucleation sites. Derivatization used to be among the common methods in resolution in the past; here a racemate is reacted with an enantiopure compound resulting in formation of diastereomeric compounds that can be separated by physical processes. Enzymatic resolution involves mixing the racemate with a particular enzyme (protein) which reacts with one enantiomer and not the other; the resulting compound mixture is easily separated by physical processes. Apart from prep applications, chromatography is 2

by far the method of choice due to its ease and versatility, the different enantiomers in the racemate interact differently with the chiral stationary phase resulting in different elution times.

1.2 Chiral pool

The second method is utilizing what is called a chiral pool.17 Here an enantiopure compound is synthesized from readily available chiral starting materials like amino acids and sugars.

1.3 Chiral auxiliary18

The third method is the use of chiral auxiliaries:19 a chiral compound is added to the reaction mixture and forms an adduct with the starting material thereby dictating the face of attack by other species in the subsequent steps. At the end the auxiliary is cleaved off to get the final chiral target molecule.

1.4 Kinetic and dynamic resolution

The other method which has gained popularity of late is kinetic and dynamic resolution.20 In kinetic resolution a catalyst interacts with both enantiomers in the racemate but only the association of one enantiomer has a much lower activation energy to be converted to final product that can be separated from the starting materials. While dynamic resolution is similar to kinetic resolution, the only difference is that there is an equilibrium that exists between the two starting

enantiomers so that 100% conversion to a single enantiomer is possible. It is vital to note that the concept of Kinetic Dynamic Resolution (KDR) has been proved to be a valuable tool in asymmetric synthesis.21

1.5 Asymmetric catalysis

The last but not least way of acquiring chiral compounds is by asymmetric catalysis. This is the transformation of non-chiral entities such as prochirals and racemates via one or more reactions to produce chiral products by using minute amounts of an enantiomeric rich catalyst.20 The ground breaking pioneering in this category can be attributed to Trost, Sharpless, Noyori, Kagan, Knowles, and Izumi.22 Some of their significant contributions in homogeneous enantioselective catalysis were recognized and lead to 2001 Nobel-Prize in chemistry by R. Noyori and W. S. Knowles for chiral catalyzed hydrogenation and K. B. Sharpless for asymmetric oxidation.23 There are basically three classes of asymmetric catalysis; biocatalysis,24 metal-ligand complexes22 and organocatalysis.25

1.5.1. Biocatalysis

In biocatalysis the use of enzymes (proteins) is a major focus. Unlike as already discussed above in which enzymes are used in resolving a racemate, the enzymes here are used to effect one or more transformations of a particular substrate in a stereo-specific manner into a chiral product.26,27 Stewart28 and coworkers reported a stereoselective reduction of an MBH adduct into β-hydroxyl ketones with greater than 99% ee (Scheme 1.5.1.1).

1.5.2 Chiral metal complexes

The use of metal-ligand complexes as catalysts has been a subject of interest since the beginning of the 20th century, and has resulted in a lot of reviews, articles and monographs.29,22 Usually the metals involved have 14-16 non-valence electrons. The success of these systems can be attributed to the ability of the metals to have a vacant coordinating site that can be used for coordination with the substrates or to have a labile ligand like triphenylphoshine that can easily be displaced by the substrate. In this case the easily displaced ligand serves as a reservoir for the empty orbital that can be manipulated at will. Hence, metals that act as Lewis acids bind to C=X (X=O, NR, CR2) and activate the bond towards nucleophilic attack by decreasing the LUMO energy. On the other hand, ligands usually make solubility possible, provide stereoelectronic balance on the framework and control the faces of attack of the substrates involved. The coordination ability of the metal to bring the reacting species within appropriate proximity and the face-directing capability of the ligands during attack in the transition state by the species involved has been a force to reckon with in asymmetric synthesis. As early as 1975 Knowles et al developed a complex that was used in the synthesis L-DOPA, a drug for treating Parkinson’s disease, (Scheme 1.5.2.2)30. Using the metal complex approach, moderate to excellent stereoselectivity has been achieved in many reactions such as hydrogenation, alkylation, reduction and oxidation. 31,32 Perhaps the most common

and influential rigid chiral rich ligands (privileged ligands)33 in asymmetric 34-36 37 synthesis has been C2–symmetric bisoxazoline ligands like Box , PyBox , semicorrin,38 Salens39, BINAP40, and their derivatives (Fig.1.5.2.1).

1.5.3 Organocatalysis

In organocatalysis the transformation is aided by purely organic molecules which simply donate protons or electrons to the substrate or transition state leading to the product formed stereoselectively. This encompasses Lewis acid/base catalysts and Brønsted acid/base catalysts. This area has grown at a fast pace in the past decade.25 Organocatalysis can be further divided into two major categories based on the mode in which they interact with the substrate or transition state: Covalent organocatalysis and non- covalent organocatalysis. In the former a catalyst forms a covalent bond with the substrate or transition state as is the case in proline catalyzed reactions via an enamine intermediate41 or iminium ion catalysis (Fig.1.5.3.2).42 While the latter purely relies on non-covalent interaction like sharing of an electron pair or hydrogen bonding (Fig.1.5.3.2). 43-45

1.5.3.1 Chiral Lewis base/acid catalysis

At the heart of organocatalysis by Lewis bases is the enamine/iminium ion formation. Even though the use of enamine as a catalyst dates to the 1970s when Hajos-Parrish-Eder-Sauer-Wiechert carried out a proline catalyzed intramolecular aldol reaction,46 it is only in 2000 when List, Barbas and Lerner47 were able to do an intermolecular aldol reaction version that resulted in enamine catalysis gaining a

spotlight in the scientific community (Scheme 1.5.3.1.3). The enamine is readily formed reversibly by a condensation between a primary or secondary amine with aldehyde or ketone bearing an enolizable proton at the α position. Initially an imine or iminium ion is formed that readily loses a proton to form a more stable enamine (Scheme 1.5.3.1.4).

Two important characteristics of these intermediates that have made them successful in catalysis are their highly reactive nature as carbon-based nucleophiles and the ease of hydrolysis. Once generated, they can react with many electrophiles, and the amine can easily be hydrolyzed to get the desired product. Their reactivity is governed by π–lone pair interaction which results in high HOMO-raising effect.48 For this reason, there are numerous examples of pyrrolidine-based organocatalysts compared to piperidine and aliphatic amine derivative counterparts. In case of the iminium ion intermediates, these are usually generated 8

mostly from the secondary amines, though primary amines are also used. The underlying property that dictates iminium ion/imine intermediate is the type of aldehyde or ketone used which should not possess an enolizable proton at the α- position. Consequently, iminium/imine intermediates are popular with α,β - unsaturated carbonyls leading to 1, 2 or 1,4 condensation and cycloadditions49. It is important to note that the catalytic cycles followed by both enamine and iminium ion intermediate show some similarities (Fig. 1.5.3.1.3).25

By simply introducing chirality in the amine used, subsequent transformations can be achieved stereoselectively. The stereocontrol in these reactions can be controlled by two means: either by introducing steric bulkiness on the amine or having H-bonding substituent within the enamine moiety. While more basic

amines seldom require a cocatalyst during enamine generation, but less basic amines usually need a cocatalyst (Brønsted or Lewis acids).50,51 These help in the formation of the enamine by shifting the equilibrium to the right. Apart from the aldol reaction that is easily done via enamine approach, other reactions have been explored in detail like Michael addition, Mannich-like reactions52 and α- functionalization of aldehydes and ketones: for example, amination, hydroxylation, sulfenylation and halogenations.53 Even some domino reactions have been reported.54

Since List et al.47 rekindled the enamine chemistry in 2000, there has been remarkable catalysts designed with extraordinary stereocontrol; however, most of them still fall short. There are usually serious side reactions that have to be dealt with if both the donor and the acceptor possess an enolizable proton. More importantly, most, if not all, of them have a limited substrate scope. This can be attributed to the fact that for a ketone–aldehyde condensation the equilibrium barely lies to the right and, worse, the ketone–ketone condensations are barely reactive since the equilibrium lies to the left unless activated. In terms of aldol reactions, for example, aldehyde–ketone condensation usually produces anti products and for the crossed aldol with aliphatic aldehydes the syn variant is yet to be realized.

Another activation mode by Lewis bases is via non-covalent bonding. This is less common due to the limited number of organic functional groups that can interact non-covalently with Lewis bases. Here, organosilanes are more common, this is due to their ability to exhibit extended coordination fashion. For this reason they can bind to a number of species bringing them within a certain optimum proximity for a reaction to happen and chiral induction. Stravenger et al. in 200055 carried out

an aldol reaction between organosilanes and aldehydes with excellent yields and selectivity (Scheme 1.5.3.1.5).

Even though catalysis by Lewis acids has become synonymous with the use of metals such as aluminum chloride, zinc chloride and titanium chloride, there are certain compounds having silyl56, phoshonium57 and carbenium groups that may behave like Lewis acids. Catalysis by the “environmental friendly” ionic liquids also belong to this category.58 By definition, Lewis acids activate the substrates by interaction between their empty orbital and the filled orbital of the substrate.59 For example, Mukaiyama and coworkers used the trityl perchlorate and were able to carry out aldol and Michael transformations with moderate stereoselectivity (Scheme 1.5.3.1.6).60

1.5.3.2 Chiral Brønsted acid catalysis

Activation of substrates by Brønsted acids can be divided into two categories: activation by hydrogen bond donation and protonation of the prochiral substrates (Fig.1.5.3.2.4).

The former is very popular and is inspired by the enzymatic reactions in biological systems. This follows general Brønsted acid activation where the proton is transferred partially (hydrogen bonding) in the rate determining step. These are neutral Brønsted acids and good examples include Scott Miller’s peptide-based catalysts61,62, Rawal et al TADDOL63, ureas and thioureas (Fig. 1.5.3.2.5) developed by Jacobsen for the Morita-Baylis-Hillman reaction (MBH) and Henry reactions.64 These have been widely utilized. For example, Tekamoto et al reported the use of thiourea based catalysts for Michael addition of activated methylene compounds to α-β unsaturated compounds imides with activation via hydrogen bonding (Scheme 1.5.3.2.7).65

In the latter specifically called Brønsted acid activation, protonation occurs during the pre-equilibrium step reversibly before the nucleophile attacks. These are strong Brønsted acids. Examples include the chiral phosphoric acids developed by Akiyama at el. and Terada at el. independently for the Mannich reaction. 66,67 Alcohol-based have also been developed like biphenol or BINOL.68 These are moderate proton donors compared to the phosphoric-based and have been used in Morita–Baylis-Hilman reaction with moderate stereoselectivity (Scheme 1.5.3.2.8).69 Fine tuning of the Brønsted acidity to widen the reaction repertoire resulted into other stronger acids being developed by Yamamoto in 200670 and Maruoka in 200771 (Fig. 1.5.3.2.6).

In general Brønsted catalysis, hydrogen bonding can serve three main purposes in catalysis: first, it can reorganize the spatial arrangements of the reactants to an appropriate order leading to enhanced reactivity and selectivity. Secondly, once hydrogen bonds are formed there is a change in the electron densities leading to polarization and this can activate the reactants. Thirdly, hydrogen bonds are weak (<1-40 kcal/mol) hence they are flexible and can expand or contract. This flexibility makes them capable to stabilize the charges that develop in the transition states and intermediates.72

The less popular way of using Brønsted acids to carry out transformations enantioselectively is the use of the acids as the proton source. A classic example was demonstrated by Plaquevent and coworkers73 in which they were able to obtain the product with as high as 94% ee (Scheme 1.5.3.2.9). Unlike in the previous situation where the proton undergoes a temporary and reversible interaction with the substrate and after the nucleophilic attack, here the proton is

easily released leading to high turnover. The biggest problem here was the turnover of the catalyst. To solve this problem, a careful pKa balance in the reaction mixture and slow addition of the acid were employed.74 Use of auxiliary acids to enhance acidity has also been employed by a number of research groups.75 However, the challenge to develop catalysts with much wider substrate scope still remains.

1.6 Bifunctional catalysts

To solve some of the problems that the afore discussed catalytic systems, there has been a new trend of designing catalysts to possess two or more reaction promoting functionalities within the same molecule. The functionalities operate in synergy resulting in a specifically controlled transition state leading to more efficient and stereoselective catalysts.76,77 Nature has utilized the idea of bi/polyfunctional catalysis and has made reactions that would be unthinkable to happen possible. Enzymes carry out their metabolic transformations using two or more active sites that activate the reaction species in synergy. 78 A good example is aldolase that

catalyzes an asymmetric aldol reaction between ketones as donors and aldehydes as acceptors.79,80 In bi/polyfunctional catalysis distance and orientation are cardinal to the catalyst activity and selectivity.

1.6.1 Cinchona alkaloids as bifunctional catalysts

Perhaps the most common bifunctional catalyst is one that involves an acidic and a basic functionality within the same molecule thereby activating nucleophiles and electrophiles simultaneously (Fig. 1.6.1.7). A classic example is the Cinchona alkaloids whose catalytic activities can be dated back to the 191381 but only became more studied and developed by Wynberg in the 1970s and 1980s 82 when he reported a Michael addition between nitro alkanes and methylvinylketone (MVK). By 1981 he reported the stereoselective version of 1,2- and 1,4-additions of aromatic thiols to cycloalkenones catalyzed by cinchonidine (Scheme 1.6.1.10).83

As can be seen in Scheme 1.6.1.10, the catalyst played a dual role via deprotonating the thiol making it more nucleophilic and activating the ketone through H-bonding. This elegant work that Wynberg and coworkers pioneered the understanding of bifunctional catalysts and lead to the design of new cinchona- alkaloid based catalysts.84 For example, Hatakeyama did a modification on the naturally occurring quinidine and was able to carry out MBH reaction to obtain enantiomerically enriched α-methylene–β-hydroxyl) esters up to 99% ee.(Scheme1.6.1.11).85 It is suggested that the generation of the ether bond between C8-C9 made the catalyst more rigid, a needed property for catalysts.

Deng et al.86 presented the first conjugate addition using organocatalysts (quinine) of α-substituted β-ketoester to α β-unsaturated ketones. A manipulation of quinine led to results up to 95% yield and 99% ee (Scheme 1.6.1.12)

Jørgensen and coworkers also developed quinine derivatives for aza-Michael addition of hydrozones to cyclic enones. With their design they were able to get excellent yield (up to 92%) and moderate enatioselectivity (up to 85% ee).87 A number of other asymmetric transformations have been performed by cinchona including conjugate additions with imines88, diazo substrates89, nitriles90, α- ketoesters,91 2-pyrones,92 nitro alkenes and sulfones. 93

A noteworthy modification to the cinchona alkaloid catalyst was the introduction of urea and the thiourea groups as hydrogen bond donors. While as this use of urea as hydrogen bond donors was well documented, it is only in 1991 when Jørgensen et al did a detailed study on the hydrogen bond donor properties that different groups became interested in these systems. In 2005 Cannon et al. demonstrated the addition of dimethylmalonates to nitro alkenes with excellent yields and selectivity (Scheme1.6.1.13).94 Apart from the hydrogen attached to nitrogen being important

in the transformation, it was also observed that the presence of a non-Lewis acidic electron withdrawing substituents on the aryl groups were also vital.

Wang et al. demonstrated further the versatility of the thiourea cinchona derived bifunctional catalyst by performing a domino Michael-aldol reaction generating three stereogenic centers with as little as 1mol % catalyst loading with excellent yields and stereoselectivity (Scheme 1.6.1.14).95

1.6.2. Chiral cyclohexane-diamine based bifunctional catalysts

Jørgensen et al. reported a novel cyclohexane-diamine based catalyst for the Strecker reaction in 2000. The cardinal groups responsible for activity and stereoselectivity are the thiourea group as a hydrogen bond donor and the amine as the base to activate the nucleophile (Fig. 1.6.2.8).

The first enantioselective Michael additions involving α,β–unsaturated imides and malonitriles was reported by Takemoto et al. in 2005 (Scheme 1.6.2.15). The reaction was observed to have a wider substrate scope with excellent yields and stereoselectivity.96

The same group also had done a Michael reaction between nitro-olefins and malonates with up to 93% ee and 85% yield. But, more importantly, they demonstrated the dual synergistic activity of the catalyst in that when either of the cardinal functional groups was removed, both activity and selectivity went down.97 Since then the chiral cyclohexane-diamine catalysts have been applied to many reactions like Mannich98 and aza-Henry99 reactions.

1.6.3. Chiral binaphthyl-based amine catalysts

Sasai et al. developed a novel type of bifunctional catalyst for aza-MBH reaction of αβ-unsaturated carbonyls and N-tosylimines. He used a tertiary amine like the other cases discussed above, but he incorporated (S)-Binol as a Brønsted acid (Scheme 1.6.3.16).100 With this system they attained up to 95% ee and 96% yield

Wang and coworkers also developed an elegant bifunctional catalyst that possessed a binaphthyl derived amines and could promote MBH reaction between αβ- unsaturated carbonyls and aldehydes with excellent results (Scheme 1.6.3.17).101 The same catalyst they developed was also observed to be good for Michael addition between 2,4-pentandiones and nitro-olefins with as little as 1 mol% catalyst loading but giving excellent yields and remarkable enantioselectivity (Scheme 1.6.3.18).102

1.6.4. Proline and its derivatives

Perhaps one of the simplest and yet efficient bifunctional organocatalysts is proline and its derivatives. Ever since the interest in it was revived in 2000 by List et al., there has been a tremendous development in the use of amino acids as catalysts. This is not very surprising because Mother Nature’s catalysts (enzymes) carry out reactions with excellent stereocontrol.103,104 For this reason there has been a quest in the scientific community to imitate the high efficiency that enzymes exhibit in catalysis. In 1974 Hajos and Parrish reported that (S) proline could catalyze Robinson annulation of meso-triones giving excellent yield of 100% and 93% ee. The bicyclic ketol was later converted to an enone under reflux and remarkably the enantiomeric excess still remained high (Scheme 1.6.4.19).

The use of proline as an efficient bifunctional catalyst was further explored by List et al. who performed an intermolecular aldol condensation between acetone and aromatic aldehydes that give moderate results up to 68% yield and 76% ee. Remarkably, when they extended the substrate scope to aliphatic aldehydes, excellent results were obtained up to 97% yield and 96% ee (Scheme1.6.4.20). The mechanism involves the formation of the enamine between proline and the acetone then the hydrogen bonding between the carboxyl group and the aldehyde via a Zimmerman–Traxler type transitional step which is the chiral transferring step, the final steps just lead to hydrolysis generating the aldol adduct and proline

The synergistic effect that bifunctional catalysts exhibit have resulted in chemical transformations that could have not been possible without the cooperative effect. Thanks to the thoughtful mechanistic considerations and understanding of the already existing monofunctional catalysts. The use of amino acids and their

derivative in organic transformations have gained popularity since 2000 due to their relatively high abundance and ease of handling. However, the fore discussed catalysts still suffer a lot of short falls: higher catalytic loading, limited substrate scope, longer reaction times and that most of them have not been explored in more complex synthetic protocols. For bifunctional catalysts, fine tuning the Brønsted acidity is usually challenging due to limited options in manipulating Brønsted acidity. Nevertheless, it is the same limitations that have inspired researchers to come up with novel ideas resulting in excellent catalysts and will continue to inspire creativity in science.

1.7 Combining transition metal catalysis and Organocatalysis

The use of transition metals in asymmetric catalysis has been explored to greater lengths and has proven to be a remarkable way to form C-C and carbon– heteroatom bonds, which is a cornerstone of organic synthesis.105,106 The use of small organic molecules has also attracted a lot of attention since 2000. This has resulted into the development of bi/polyfunctional organic catalysts.

1.7.1 Enamine-transition metal catalysis

However, a lesser explored avenue has been the combining of enamine catalysts with transition metals. This is a promising strategy because both catalytic systems involved have been studied extensively and have shown excellent results that combining them is logical and would in principle increase the potential of carrying out transformations that neither the transitional metal catalysis nor the organocatalysis could perform alone. In 2005, Cordova and coworkers showed the first example of combining enamine and transitional metal catalysis to perform a 25

transformation (Scheme 1.7.1.21).107 Their outstanding work involved direct enamine intermediate in an intermolecular α-alkylation of cyclic ketones and aldehydes. Despite the products being racemates, the yields were pretty good (up to 85%).

The authors proposed that an enamine is generated between pyrollidine and the aldehyde or ketone which attacks the electrophile formed in situ from the palladium and allyl acetate. Subsequent steps involve hydrolysis of the iminium intermediate followed by regeneration of the pyrollidine and Pd(0). Group IIB metals (Cu, Ag, and Au) have also been merged with enamine chemistry. One example was from Wu et al. who developed the first reaction in which enamine chemistry was combined with π-acidic transition metals. In one pot they synthesized 1, 2–dihydroisoquinoline derivatives via a condensation of ketones amine and 2-alkyl aldehydes.108 The key steps in this domino transformation are the generation of the enamine which attacks the imine followed by intramolecular Mannich-like reaction involving an activated alkyne by the Ag. The subsequent reactions involve the hydrolysis of the proline and the Ag (I) (Scheme 1.7.1.22)

Scheme 1.7.1.22. A domino reaction involving an enamine and a transition metal

The methods discussed above all involve a metal acting as a π acid to activate the electrophile by either coordinating with the double or with the triple bonds. Other metals have been explored such as Au(I)109, Cu(I)110, and Ir(I)111 resulting in intramolecular and some intermolecular transformations. It is vital to note that in all the above examples stated the major core strategy is the use of the soft/hard approach to avoid self-quenching reaction between the acid and the base.

Three other methods involving enamine-metal systems have been reported. However, these function differently as compared to the ones already discussed so that they seem to fall in their own category. Instead of having the enamine and the metal involved at some point in the same moiety of the intermediate, the catalytic cycle can be divided into two: one part is an organocatalytic cycle where an enamine is the major player in the transformation and the other part is the photo redox catalytic cycle where the metal plays an important role. MacMillan and coworkers in 2007112 pioneered the enamine SOMO (Single-electron Occupied Molecular Orbital) catalysis. The enamine is generated in the usual way which is 27

oxidized to a highly reactive cationic radical electrophile, which is then condensed with a nucleophile giving high yields and excellent enantioselectivities (Scheme 1.7.1.23).

Other metals have been explored using the above strategy and photo oxidants such as Ir(III) and Ru(III). Another strategy reported in 2007 was the in situ oxidation of olefins to ketones/aldehydes which later form an enamine that reacts with an acceptor giving high yields and ee. Breit et al (Scheme 1.7.1.24) and Eilbracht’s groups reported the hydroformylation/aldol reactions independently. The potential of this method was further demonstrated by Eilbracht’s group that performed a cascade hydroformylation and Mannich reactions under one pot with moderate yields and enatioselectivities.113

1.7.2. Metal catalysis and chiral Brønsted acid counter anion

In 2007, Toste and coworkers introduced a remarkable approach of asymmetric counter–anion-directed catalysis (ACDC) using gold. The idea is to use a chiral counter-anion of a metal salt to control the stereoselectivity in an organic transformation (Fig. 1.7.2.9).114 Even though the use of gold in alkenes and alkynes activation has been a hot topic for some time,115 the stereo induction using the traditional chiral ligands has always been a challenge due to its linear coordination geometry which puts ligands at 180o from the substrate. As a result, only limited reports are found using chiral phosphorus ligands with low to moderate enantioselectivities.116 The utility of this method was demonstrated by carrying out hydroalkoxylation of allenes using (R)–TIRP [3, 3’–bis (2,4,6- triisopropylphenyl)-1,1’–binaphthyl-2,2’–diyl hydrogen phosphate] as a counter anion giving excellent yields and enantioselectivity (Scheme 1.7.2.25)

The versatility of the ACDC in synthesis was recently demonstrated by List and coworkers who developed a reaction in which a quaternary stereogenic carbon center was formed with excellent yields and selectivity (Scheme 1.7.2.25).117 The aldehyde and the amine condenses to generate a protonated enamine which coordinated to Pd(0) and (R)-TRIP via a transition state shown in (Scheme 1.7.2.26). Using Mn(III) and salens they were able to carry out enantionselective epoxidation of alkenes with excellent results up to 98% yield and 96% ee.118 With this method on hand, they carried out a concise synthesis of a natural product (+)- cuperane via Rh-catalyzed intramolecular hydroacylation (Scheme 1.7.2.26).

A number of novel transformations have been reported in which transition-metals and organo compounds are combined to effect a synthesis. In a nutshell, their mechanisms are similar to the ones already outlined above.119

1.8 Enamine-metal Lewis acid bifunctional catalysts

1.8.0 Introduction

Even though the use of cooperative effects in catalysis has resulted in remarkable designs of catalysts giving some outstanding results in both activity and selectivity they still suffer from a number of disadvantages: higher catalytic loading, longer reaction times, limited options for catalytic manipulation, and fine tuning and, above all, limited substrate scope. However, the fact that the synergy in catalysis can be explored mimicking Mother Nature’s protocols is a sign that cooperative catalysis in organic synthesis warrants further exploration due to its potential.

Our research purpose is to design enamine-metal Lewis acid bifunctional catalyst within the same molecule. These bifunctional catalysts are expected to be more active due to their unique mode of activation and yet easy to manipulate for a wider substrate scope than conventional bifunctional catalysts. Hence, we can be able to explore challenging carbon-carbon and carbon–heteroatom bond formation reactions.

This is a formidable task due to the simultaneous requirements of distance, orientation, and interaction of the functional groups without deactivating each other.120-124

Even if the strategy of combining organo-enamine with metal Lewis acid has been successfully employed, its greatest drawback has been the uncompromised requirement of hard/soft combination to avoid acid-base self-quenching. This ultimately reduces the catalysts’ substrate scopes hence its potential. In our novel design, we solve this acid-base quenching problem by tethering a variety of Lewis bases (primary and secondary amine) and a chelating ligand to serve as a ‘trap’ for 32

the incoming metal. By so doing, the Lewis base is sterically unavailable to the metal (Fig. 1.8.0.10 (a)). Thus, ligand design is critical to the catalyst function. We hope that our new ligands may add to the already existing small library of the BINAP, Salens and triazole based ligands that have been successful.

With this blueprint, the Lewis acid and the base will be brought in closer proximity within the same moiety without interacting with each other. In cooperating a metal within the same molecule also assembles the system into slightly rigid framework, a much needed property of the catalysts. This design is complementary to the already existing protocols, but provides us with a number of unique advantages over the prior systems. The hardness/softness of the metal is not an issue due to its design and the Lewis acidity can be tuned at will by simply changing the type of a metal used. In principle, stronger Lewis acids such as Al(III) and much weaker Cu(I) can be explored increasing the catalyst’s potential. Another great advantage of this system is that it changes a much harder intermolecular reaction to a more efficient intramolecular-like reaction (Fig. 1.8.0.10(b)). This system can thereby expand substrate scope of a reaction. Traditionally, enamine based organocatalysts 33

activate the acceptors by hydrogen bonding.125-129 On the contrary, Lewis acids which are much stronger activating agents are used in the reaction. By doing so higher activation of the acceptors is achieved resulting in much faster reactions and wider substrate scope.

The core requisite for our design is the metal chelating to the ligand. The idea of “trapping” the metal in the scaffold has been demonstrated by other groups.130 In 1995, Kelly and coworkers synthesized and obtained single X- ray crystal structure of a square planar metal complex of 2,2’-bipyridyl derivatives (Scheme 1.8.0.27).131 The same idea was also used by Manessi-Zoupa et al. in 2001 who showed that N,N’ –(2-pyridyl)urea could serve as a bidentate ligand and was successfully complexed with Cu(II), Co(II), Zn(II), and Ni(II) to afford mononuclear trans-metal complexes (Fig. 1.8.0.11).132 The urea oxygen and one pyridyl nitrogen acted as the chelating atoms, while the other pyridyl nitrogen did not participate in the coordination: a fact that authenticated our design and was later proved by other methods.

Our design takes advantage of the two well-studied categories of catalysis in asymmetric organic synthesis: the enamine approach and metal coordination complexes. We take advantage of the enamine chemistry because it allows us to perform “direct” reactions, eliminating one of the biggest problems in C-C bond formation involving carbonyl groups which is the pre-formation of enols and enol analogues; these are difficult to handle requiring lower temperatures and anhydrous conditions. The metal-Lewis acid component on the other hand, offers structural properties and provides a higher activation of electrophiles enabling even difficult reactions to be explored. Given the unique activation modes of the organocatalysis and the metal catalysis, the combination of these two areas holds the greatest potential of achieving organic transformations that are not possible through organocatalysis or metal catalysis alone.

Our systems were evaluated on aldol reaction which is one of the most important carbon-carbon bond formation reactions in organic synthesis.133,134 Although the aldol reaction is one of the most studied reactions in modern chemistry, it still faces numerous challenges in chemo-, regio-, and enantioselectivity. 35

Results and Discussion

1.8.1 Catalysts based on tetradentate secondary amine ligand system: 6,6’ – diamino-2,2’-bipyridine (Dabp) (105)

Since organocatalysis was once again brought into light in 2000,47,49,135,136 tremendous progress has been made in the area of asymmetric synthesis using these small but efficient molecules in different reaction types.137-139,42,43 Thus far, proline has enjoyed supremacy as a model catalyst on which most of the designed catalysts has been based.140-154This has been due to its bifunctional nature and the higher HOMO rising effects of the pyrrolidine ring. Furthermore, it is cheap, nontoxic, environmentally friendly, readily available in both enantiomeric forms, features easy to handle reaction conditions (usually at room temperature), can easily be removed by aqueous work up, and no prior modifications of the substrates like silylation are needed. It is in view of these advantages that we decided to design our first catalyst based on amino acid proline (Fig. 1.8.1.12), hoping that we can be able to solve some of the challenges in this field using our design strategy.

Retrosynthesis of the ligand 105 is illustrated in Scheme 1.8.1.28. We envisioned that the target molecule can be obtained using the convergent approach by

synthesizing the diamine 105 and the proline derivative 108 separately then coupling the two at the end.

The diamine 107 can be obtained via a series of transformations from the readily commercially available 2, 6–dibromopyridine. The N-methyl proline 108 can be realized by a one-step reaction from proline.

Scheme 1.8.1.28. Retro synthesis of 105

1.8.1.1 Synthesis of 6,6’ –diamino-2,2’bipyridine( Dadp) 107

The synthesis starts with the commercially available 2,6-didromopyridine via four steps following a well-known reported procedure by Holm et al.155 The first step is the n-butyl lithium and copper chloride mediated self-condensing of the 2,6- didromopyridine in diethyl ether at -78o C . The product dibromo-2, 2’-bipyrindine undergoes substitution by hydrazine followed by oxidation to azide . The final step is the reduction with hydrogen catalyzed by Pd/C to 107 in 24% overall yield.

N-methyl proline 108 was synthesized by a reported procedure156 in which L- proline reacted with 40% aqueous formaldehyde in the presence of methanol followed by reduction using hydrogen on palladium carbon giving a high yield of 108 up to 90% (Scheme 1.8.1.30).

1.8.1.1a Attempted synthesis of (2R,2'S)-N,N'-([2,2'-bipyridine]-6,6'-diyl)bis(1- methylpyrrolidine-2-carboxamide) (105)

Having the two substrates needed for the realization of our target molecule 105, we attempted to make the final ligand. Unfortunately, all the methods using different coupling reagents (Table 1.8.1.1a.1) where unsuccessful, usually unidentified compounds and some starting materials resulted.

Entry Reagent Solvent

1 Thionyl Chloride THF, pyridine

2 Phosphoryl Chloride Pyridine

3 Ethylchloroformate DCM/TEA

4 BOP DCM/TEA

Table. 1.8.1.1a.1. Coupling reagents used for ligand 105

Fortunately, a test coupling reaction between Dadp(107) and commercially available benzoyl chloride was successful. For that reason we then decided to synthesize Boc proline (Scheme 1.8.1.1a.31) and acquired commercially available Cbz proline instead of N-methyl proline. The idea was that both of these protecting groups could easily be removed and the methyl be introduced back in the last step after the coupling is done. 39

1.8.1.1b Attempted synthesis of (2R,2'S)-N,N'-([2,2'-bipyridine]-6,6'- diyl)bis(1- methylpyrrolidine-2-carboxamide) 105

The first part of the synthesis was successful using both Boc and Cbz proline giving 45% and 70% yield respectively, confirmed by NMR and MS spectra. However, the introduction of the methyl group in the last step using aqueous formaldehyde proved futile, unidentified compounds and some starting material was observed.

Since most of the proline derivatives that have been extensively explored and have demonstrated their versatility are secondary amines, we then decide to go and test

our ligand 117 on direct asymmetric aldol reaction between acetone and 4- nitrobenzaldehyde (Table 1.8.1.1a.2)

Entry Metal Time [h] Solvent Yield [%] ee [%]

1 - 48 Neat 18 50

2 Cu(OTf)2 48 MeOH 43 67

3 Zn(OAc)2 48 MeOH 74 17

4 Co(ClO4)2 48 MeOH 84 64

5 Cu(SbF6)2 48 MeOH 36 69

6 Ni(ClO4)2 48 MeOH 45 55

8 Cu(OTF)2 72 THF 40 57

9 Co(ClO4)2 48 THF 49 58

10 Cu(SbF6)2 48 THF 96 65

Table 1.8.1.1a.2. Metal screening. 0.5 mL acetone, 0.2mmol 4-nitrobenzaldehyde, rt

We started our investigation by carrying out the reaction under neat conditions with just the ligand without a metal (Table 1.8.1.1a.2, entry 1). After 48 hours we obtained the product though in low yield 18% but moderate enantioselectivity (50% ee, entry 1). We then explored different metal salts in different solvents. This was done by mixing the ligand and the metal in a 1:1 molar ratio in a particular solvent and then stirring the mixture for about 4-5 hours for complex formation, after which 0.2mmol of the substrate (4-nitrobenzaldehyde) was added. Most of the metals explored actually gave moderate to excellent yields. Co(ClO4)2 in THF gave good yield 84% and moderate selectivity 64% ee (entry 4). The best conversion was achieved when Cu(SbF6)2 was used in THF up to 96% yield, disappointingly, selectivity still remained moderate 65% ee. Since the Co(ClO4)2 and Cu(SbF6)2 gave the best results, they were selected for further investigations.

Using Co(ClO4)2 as the metal, different solvents were explored and the results are organized in Table 1.8.1.1b.3.

Entry Time Solvent Yield [%] ee [%]

1 7days DMSO 24 71

2 7days DMF 21 75

3 48h Isopropanol 74 61

4 7days Ethanol 62 58

5 48h Tert -Butanol 86 56

6a 20h Isopropanol 84 57

Table 1.8.1.1b.3. Solvent screening with Co(ClO4)2, [a] 20 mol% catalyst

The best enantioselectivity was observed in DMF 75% ee and DMSO 71% ee. However, these solvents gave the lowest yields (21% and 24%) respectively even after 7 days (Table 1.8.1.1b.3. entries 1 and 2). On the contrary, isopropanol and tert-butanol showed moderate conversion leading up to 74% and 86% respectively, but stereoselectivity went down a little bit, 61% ee and 58% ee. When the catalyst loading was increased to 20 mol% in isopropanol, activity was excellent; reaction went to completion in 20 hours. Unfortunately, stereoselectivity did not improve

(entry 6). Exploring Cu(SbF6)2 in different solvents gave a similar picture as the case with Co(ClO4)2 (Table 1.8.1.1b.4)

Entry Time Solvent Yield [%] ee [%]

1 7days DMSO 19 86

2 7days DMF 50 79

3 48h Isopropanol 53 63

4 48h THF/DMF 21 82

5a 48h THF 31 82

6b 48h DMF 79 66

o Table 1.8.1.1b.4. Solvents screening with Cu(SbF6)2. [a] reaction done at 0 C. [b] 20mol% catalyst loading used.

DMF and DMSO gave higher enantioselectivities (79% ee and 86% ee) but activity was very low in both cases. Extension of the reaction time up to 7 days furnished only 50% yield for DMF and 19% yield for DMSO (Table 1.8.1.1b.4, entry 1 and 2). Increasing the catalytic loading in DMF to 20 mol% as expected increased activity giving 79% yield in 48 hours, but lower enantioselectivity (66% ee entry 6). We also surveyed mixture solvents approach using THF/DMF that gave moderate selectivity 82% ee but activity was low giving only 21% yield after 48hours.

From the two solvent screening tables, it can be concluded that there is an inverse relationship between activity and enantioselectivity, (Table 1.8.1.2b.3 entries 1 and 2 compared to entries 3 and 5 and Table 1.8.1.1b.4, entries 1, 4, and 5 compared to entries 3, 6). To solve the selectivity problem we decided to modify our ligand system by installing only one Lewis base on the moiety with a sterically bulky group like tert-butyl on the other side (Scheme 1.8.1.1b.33).

Synthesis of the new ligand started with a condensation between Dabp(107) and croctyl chloride in DCM to furnish A in 66% yield followed by coupling with Cbz proline using ethylchloroformate in THF. The last step is a deprotection of the Cbz using hydrogen on activated palladium/carbon to form 120 in 50% yield. When this new ligand was used in the direct asymmetric aldol reaction between acetone and 4-nitrobenzaldehyde, 84% yield was achieved in 72hours with 76% ee.

Even if there was no great improvement compared to the previous results (Table 1.8.1.2.4), nevertheless, we proved the principle of enamine–Lewis acid 45

bifunctional catalysis and was worthy of further investigation. Control experiment without the catalyst did not furnish any product at all. Moreover, the conditions used here were based on the other ligand system previously used. Hence, there was need to rescreen metals and solvents.

1.8.2. Catalysts based on tridentate ligand system secondary amine 157

The synthesis of 6,6’–diamino-2,2’-bipyridine (Dabp) (107), which is the starting material for ligands 117 and 120 made previously, was lengthy and some of the steps had lower yields. We then decided to design a much simpler ligand system based on tridentate coordination pattern. Three tridentate ligands were synthesized with ligand 122 possessing a C2 symmetry having two L-proline incorporated , whiles ligands 123 and 124 have a C1 symmetry and carry only one L-proline moiety. These can easily be synthesized utilizing known protocols starting from commercially available 2,6–diaminopyridine in three steps that involved two consecutive couplings followed by deprotection of the pyrolidine ring (Scheme 1.8.2.34).

To test the ligands, we decided to use the intermolecular aldol reaction as a model reaction. Preliminary experiments involved screening of different metal and ligands to establish the optimum reaction conditions just like in the previous cases.

Ligand 123 with Cu(SbF6)2 in 0.3mL. of acetone and 0.6mL of THF was found to be the best conditions. These conditions were applied to different aldehydes (Table 1.8.2.5).

Entry R1 Product, Yield [%] ee [%]

1 4-NO2C6H4 118a, 75 90

2 3-NO2C6H4 118b, 75 89

3 2-NO2C6H4 118c, 71 93

4 4-CNC6H4 118d, 95 87

5 4-CO2Me C6H4 118e, 92 87

6 4-ClC6H4 118f, 60 85

7 2,6-Cl2C6H3 118g, 73 91

8 2-naphthyl 118h, 73 74

9 4-MeC6H4 118i, 48 58

Table 1.8.2.5. Aldehyde scope of the direct asymmetric aldol reaction.

The reaction was carried out with (0.2mmol) aldehyde and acetone (0.3mL) in 0.6mL THF at r.t. for 24-72hrs. [a] At 0 oC.

It can be seen from the table that both electron-rich and electron-poor aldehydes reacted smoothly furnishing the desired product 118. Higher yields (60-95%) and enantioselectivities (85-91%) were observed in reactions involving electron deficient aldehydes (Table 1.8.2.5. entries 1-7) compared to those transformations

that involving electron-rich aldehydes that showed lower yields (48-73%) and lower selectivity (58-74% ee) (entries 8 & 9).

This catalytic system was also investigated with acyclic donors like butanone (Scheme 1.8.2.36). The results were excellent with combined yields as high as 95% and selectivity greater than 30/1 (anti/syn) diastereoselectivity and greater than 99% ee for the anti diastereomer.

Entry R1 Anti/Syn Product,Yield [%][a] ee [%][d]

1 4-NO2C6H4 8:1 129a, 96 91

2 3-NO2C6H4 9:1 129b, 96 81

3 2-NO2C6H4 8:1 129c, 96 83

4 4-CNC6H4 10:1 129d, 91 84

5 4-CO2Me C6H4 8:1 129e, 82 80

6 4-ClC6H4 6:1 129f, 80 82

7 2,6-Cl2C6H3 >30:1 129g, 95 86

8 2-naphthyl 6:1 129h, 71 76

9 C6H5 5:1 129i, 70 71

Table 1.8.2.6. Aldehyde scope with ligand 123. The reaction was carried out with (0.2mmol) aldehyde and acetone (0.3mL) in 0.6mL THF at r.t. for 24-72hrs. [a] Combined yield.

When cyclohexanone was used as a donor (Table 1.8.2.6) a similar trend was observed as the case with acetone as a donor. We observed higher stereoselectivities and yields when electron poor acceptors were used as opposed to electron rich acceptors. 50

1.8.3 Catalyst based on tridentate ligand system primary amine 158

In our continuing effort in bridging the gap between the traditional but well established transition metal catalysis and the new but booming amino catalysis, we designed another tridentate ligand catalytic system based on primary amines. Use of primary amines is prevalent in nature. For example, type I aldolase and type II aldolase catalyzes carbon-carbon formation with excellent stereocontrol utilizing different activation modes to aid the transformation.102, 103 Type I aldolase utilizes primary amino group on the amino acid lysine via enamine mechanism, while as type II aldolase uses a zinc cofactor as a Lewis acid as a cardinal activation mode.

While the secondary amine (proline) derived amino catalysts have been extensively studied in details,47,42, 133 136, 159 their primary counterparts have remained less developed despite their potential.160 161 The unique activation mode of primary amine derived organocatalysts has resulted into unprecedented selectivity and activities as demonstrated in the reactions like aldol and Mannich.162-171However, they show a much narrower substrate scope and hence lower activity in some reactions as compared to the secondary-amine-based catalysis.

Six tridentate ligands (Fig.1.8.3.13) were synthesized all bearing one or two natural amino acids. Ligands 130 and 131 were readily synthesized starting with 2,6–diamino-pyridine and coupling to an appropriate amino acids using an appropriate acyl chloride (Scheme 1.8.3.37).

Ligand 131 involved coupling to N-Cbz L-valine followed by a second coupling of N–Boc protected phenylalanine, then selective deprotection of the Cbz group using hydrogen, Pd/C (Scheme 1.8.1.38).

Ligand 134 was made by a coupling to an excess of Boc–protected phenylalanine followed by deprotection of the Boc group

These were then tested on the asymmetric direct aldol reaction between cyclohexanone and 4-nitrobenzaldehyde. Ligand 130c with Cu(SbF6)2 under neat conditions were the best conditions giving 90% yield in 12 hours, greater than 99 to 1 anti/syn ratio, and 95% ee. These conditions were used with different aldehydes, results are shown in (Table 1.8.3.7).

Entry R1 Anti/Syn Product Yield [%] ee [%]

1 4-NO2C6H4 >99:1 129a, 90 95

2 3-NO2C6H4 20:1 129b, 90 95

3 2-NO2C6H4 >99:1 129c, 93 94

4 4-CNC6H4 12:1 129d, 93 92

5 4-CO2Me C6H4 9:1 129e, 89 94

6 4-ClC6H4 6:1 129f, 73 88

7 2,6-Cl2C6H3 12:1 129g, 98 92

8 2-naphthyl 12:1 129h, 71 90

9 C6H5 10:1 129i, 76 86

10 Br-C6H4 6:1 129j, 60 94

11 4-MeC6H4 8:1 129k, 75 83

Table 1.8.3.7. Aldehyde scope with ligand 130c. Reaction was performed with 0.2mmol of the aldehyde and 1mL of cyclohexanone at rt between 12-48 hours.

From Table1.8.3.7, we see that the electron–deficient aldehydes gave excellent results in both activity and selectivity, with yield ranging from 60-98% and diastereoselectivity of 6/1->99/1 (anti/syn) and enantioselectivity of 88-95% ee 55

(Table 1.8.3.7, entries 1-8 and 10). The electron–rich aldehydes also furnished good results, (8/1–12/1% dr, 71–75% yield, and 83– 90% ee; entries 8, 9 and 11).

When other cyclic ketones were used as donors, excellent results were also observed (Table 1.8.3 8). Using six member heterocycles, yields were 68-98%, diastereoselectivity range was 10/1-46/1, and enantioselectivity was 87-94% ee (Table 1.8.3.8, entries 2-7). Cyclopentanone also furnished the product with high enantioselectivity (86% ee); however, diastereoselectivity was lower (3/1dr) and yield was moderate (66%, entry 1.). When the catalyst system was applied to the direct aldol reaction between 4–nitrobenzaldehyde and acetone, the yield was good (84%) while the enantioselectivity was only moderate (72% ee).

Entry R1 R2, R3 Anti/Syn Product Yield [%] ee [%]

1 4-NO2C6H4 -CH2CH2- 3:1 138a, 66 86

2 4-NO2C6H4 -CH2OCH2- 10:1 138b, 97 87

3 4-NO2C6H4 -CH2SCH2- 22:1 138c, 82 94

4 2-NO2C6H4 -CH2SCH2- 25:1 138d, 76 94

5 4-CNC6H4 -CH2SCH2- 46:1 138e, 86 91

6 2-naphthyl -CH2SCH2- 34:1 138f, 57 87

7 C6H5 -CH2SCH2- 25:1 138g, 68 94

Table 1.8.3.8. Aldehyde scope with other cyclic ketones. Reaction was performed with 0.2mmol aldehyde and 0.5mmol of ketone at rt in 1mL of THF between 12- 48hrs.

In summary, this novel tridentate catalytic system was observed to be able to catalyze asymmetric direct aldol reaction between cyclic ketones and both electron –rich and electron–poor aldehydes with high activity and selectivity. Its advantages include ease of tuning, cost and no need for special reaction conditions.

1.8.4 Catalyst based on bidentate ligand system containing primary amine 172

In our continuous effort to develop enamine-metal Lewis acid multi/bifunctional catalysts, we wanted to enrich our ligand repository in order to fully utilize this new concept. We designed bidentate ligands that can easily be synthesized from readily available materials (2-aminopyridine and L amino acids). Unlike the tridentate ligands systems developed and discussed in the previous chapters, 157, 158 these are much simple with much shorter synthetic routes. Even when compared to the already existing primary amine-based organocatalysts, 160-168, 170,173-182the activity and diastereoselectivity of these catalysts were significantly enhanced for asymmetric direct aldol reactions of ketones. Seven bidentate ligands tethered with primary amines were prepared (Fig. 1.8.4.14).

The synthesis of these ligands was achieved through coupling reactions between N –Boc protected L–α amino acids and 2–amino pyridine followed by deprotection of the Boc group (Scheme 1.8.4.40). 58

We started investigating the catalytic activities of these ligands with the aldol reaction of cyclohexanone with 4-nitrobenzaldehyde in neat conditions with ligand 139a combining with different metal salts (Table 1.8.4.9).

Entry Metal Anti/Syn Product Yield [%] Anti ee [%]

1 Cu(SbF6)2 25:1 80 98

2 Cu(OTf)2 12:1 94 90

3 Co(ClO4)2 2:1 90 65

4 Ni(ClO4)2 4:1 80 61

5 Yb(OTf)3 1:1 80 25

6 Zn(OAc)2 1:1 70 70

7 FeCl2 2:1 65 83

8 Ag(OTf)2 2:1 50 80

Table 1.8.4.9. Metal screening of the reaction between cyclohexanone and 4- nitrobenzaldehyde using weak Lewis acids. 59

From Table.1.8.4.9 it can be observed that all the metal salts gave excellent yields (94-70%). However, Cu(II) salts displayed superior results in diastereoselectivity and enantioselectivity. In general selectivity varied considerably with Cu(SbF6)2 giving the best selectivity (dr 25/1, ee 95% entry 1) and Yb(Otf)3 and Zn furnishing the lowest dr of 1:1 (entries 5 and 6), the rest of the metals gave moderate results with the lowest enantioselectivity from Yb(OTf)3, (25% ee entry 5). Counter anion also played a role in determining the stereoselectivity as

Cu(SbF6)2 showed much better diastereoselectivity and enantioselectivity compared to Cu(OTf)2.

We further explored other strong Lewis acids with the hope of getting the syn product as the major product during the aldol reaction between cyclohexanone and 4-nitrobenzaldehyde (Table 1.8.4.10).

Entry Metal Anti/Syn Syn ee [%] Anti ee [%]

1 Yb(OTf)3 1:1 <5 25

2 La(OTf)3 1:1 60 42

3 Sm(OTf)3 1:1 <5 20

4 Sc(OTf)3 1:1 5 66

5 Y(OTf)3 1:1 11 32

6 Zn(OAc)2 1:1 0 70

Table 1.8.4.10. Metal screening of the reaction between 1mL cyclohexanone and 0.2mmol of 4-nitrobenzaldehyde using stronger Lewis acids at rt between 12- 48hours. All the metals gave a low diastereoselectivity (1:1 dr), and in terms of enantioselectivity, apart from La(OTf)3, which furnished a 60% ee of the syn product (Table 1.8.4.10, entry 2) the rest of the metals gave almost racemates syn products. We then screened different solvents using La(OTf)3/139a conditions (Table.1.8.4.11).

Entry Solvent Anti/Syn Syn ee [%] Anti ee [%]

1 Methanol 1:1 5 16

2 DCM 1:1 0 22

3 MeCN 1:1 <5 8

4 Toluene 1:1 <5 46

5 DMSO 2:1 <5 83

6 DMF 2:1 <5 50

7 THF 1:1 0 20

Table 1.8.4.11. Solvent screening using La(OTf)3/139a Reaction was performed with 0.2mmol of aldehyde, 0.5mL of cyclohexanone at rt between 12-48hours The best results were gotten under neat conditions. All the solvents explored gave poor results. We then focused on the anti-product that had excellent preliminary data.

Having established the best conditions for the reaction of cyclohexanone and 4– nitrobenzaldehyde giving predominantly anti product, we screened other ligands and the results are tabulated in Table 1.8.4.12.

Entry Ligand Anti/Syn Product Yield [%] Anti ee [%]

1 139a 25/1 80 98

2 139b 16:1 86 94

3 139c 16:1 90 80

4 139d 20:1 84 90

5 139e 9:1 92 90

5 139f 7:1 64 84

7 139g 9:1 90 >99

8 140 3:1 65 79

Table 1.8.4.12. Ligand screening using Cu(SbF6)2

Almost all the ligands displayed excellent results in terms of activity and selectivity. 139a and 139g showed exceptionally high activity completing the reaction in only 3 hours, much faster than the reactions catalyzed by most of the primary amine based organocatalysts which in general requires 2 to 3 days for completion.172-181 Higher activity may be attributed to the coexistence of the two primary amines in the symmetric catalytic system. 139a and 139g also provided 63

the best diastereoselectivity (25/1, dr) and enantioselectivity (>99% ee) (Table 1.8.4.12, entries 1 and 7) respectively. For comparison, L-proline tethered ligand 140 was prepared.

The secondary amine based ligand resulted in much lower activity and stereoselectivity (entry 8), another example of primary amines showing superior enamine catalytic activity than secondary amines.

In order to understand how coordination affects the activities of these catalysts, two different ligand/metal ratios (1/1 and 2/1) were used (Table 1.8.4.13). It turned out that 2/1 ligand/metal ratio gave much higher activity and selectivity. So the ligand /metal ratio of 2/1 was selected and applied for further investigations.

Entry Ligand M:L Time(h) Anti/Syn Product Yield[%] Anti ee [%]

1 139a 1:1 24 14/1 78 96

2 139a 1:2 3 25/1 80 98

3 139b 1:1 24 10/1 81 93

4 139b 1:2 10 16:1 82 94

5 139c 1:1 24 6:1 82 76

6 139c 1:2 10 16:1 90 80

Table 1.8.4.13. Investigation of the metal to ligand ratio. Reaction was performed with 0.2mmol of aldehyde, 1mL of cyclohexanone at rt between 12-48 hours We then screened a range of solvents and results are shown in Table 1.8.4.14. Even though all the solvents gave appreciable enantioselectivities, neat condition still gave the best results in activity and selectivity. Dichloromethane gave high yield and enantioselectivity, (Table 1.8.4. 14, entry 5) but diastereoselectivity and activity were lower compared to neat condition as it required 18 hours for the reaction to be completed.

Entry Solvent Anti/Syn Product Yield [%] Anti ee [%]

1 neat 25:1 80 98

2 DMSO 3/1 72 84

3 CH3CN 4:1 84 84

4 Toluene 8:1 88 95

5 Methanol 9:1 66 97

6 DCM 8:1 90 96

7 THF 6:1 76 96

8 DMF 4:1 64 86

Table 1.8.4.14. Solvent screening with Cu(SbF6)2/139a. Reaction was performed with 0.2mmol of aldehyde, 0.2mL of cyclohexanone in various solvents at rt between 12-48hours The substrate scope of the aldol reactions of cyclohexanone was then investigated using ligand 139a and 139g under the optimized conditions (Cu(SbF6)2 in neat, (Tables 1.8.4.15 and 1.8.4.16)

Entry R1 Anti/Syn Product Yield [%] ee [%]

1 4-NO2C6H4 25:1 129a, 80 98

2 3-NO2C6H4 17:1 129b, 86 96

3 2-NO2C6H4 30:1 129c, 84 95

4 4-CNC6H4 16:1 129d, 83 97

5 4-CO2Me C6H4 12:1 129e, 94 97

6 4-ClC6H4 7:1 129f, 84 97

7 2,6-Cl2C6H3 14:1 129g, 86 >99

8 Br-C6H4 12:1 129j, 70 94

9 C6H5 10:1 129i, 75 83

10 2-Naphthyl 8:1 129h, 70 92

11 4-MeC6H4 5:1 129k, 70 82

Table 1.8.4.15. Aldehyde scope with cyclohexanone using 139a/Cu(SbF6)2 Reaction was performed with 0.2mmol of aldehyde, 1mL of cyclohexanone at rt between 3-48hours

Entry R1 Anti/Syn Product,Yield [%] ee [%]

1 4-NO2C6H4 9:1 129a, 90 >99

2 3-NO2C6H4 3:1 129b, 80 >99

3 2-NO2C6H4 4:1 129c, 88 >99

4 4-CNC6H4 3:1 129d, 85 >99

5 4-CO2Me C6H4 3:1 129e, 90 >99

6 C6H5 4:1 129i, 83 89

Table 1.8.4.16. Aldehyde scope with cyclohexanone using 139g/ Cu(SbF6)2 .Reaction was performed with 0.2mmol of aldehyde, 1mL of cyclohexanone at rt between 3-48hours As shown in both tables, very good to excellent diastereoselectivity (up to 30/1 Table 1.8.4.15, entry 3) and enantioselectivity (up to >99% ee) were achieved with all electron–deficient aromatic aldehydes (Table 1.8.4.15, entry 3 and Table 1.8.4.16, entries 1-5).While 139g gave excellent enantioselectivity, it furnished lower diastereoselectivity. Electron–rich aldehydes also gave products with good diastereoselectivity and enantioselectivity (Table 1.8.4.15, entries 9-11 and Table 1.8.4.16, entry 6). For comparison, using 139g, an aldol reaction between 4– nitrobenzaldehyde and acetone furnished the product with only 81% ee. 68

With these highly active catalytic systems in hands, we decided to explore the effects of the catalyst loading on the aldol reaction between cyclohexanone and 4- nitrobenzaladehyde using ligand 139a/ Cu(SbF6)2, results are shown Table 1.8.4.17.

Entry Cat.(mol-%) Time(h) Conversion(%) Anti/Syn Yield [%] ee [%]

1 20 3 100 25:1 80 98

2 15 4 100 16:1 84 98

3 10 6 100 16:1 80 98

4 5 10 100 16:1 85 98

5 2.5 30 100 11:1 80 96

7 1.0 144 95 9:1 67 93

6 0.5 144 50 4:1 40 89

Table 1.8.4.17. Investigation of catalyst loading. Reaction was performed with 0.2mmol of aldehyde, 1mL of cyclohexanone at rt between 3-48hrs

Although an overall decreasing trend in activity and stereoselectivity is observed with less catalytic loading, stereoselectivity did not show much difference with catalytic loading between 5 to 20% (98% ee, 16/1–25/1 dr, Table 1.8.4.17, entries 1-4, and the catalyst remained very active in terms of both yield and reaction time with a loading as low as 2.5%mol% (entry 5). The performance of our catalytic system (139a/ Cu(SbF6)2 was then examined in the presence of water using the reaction between cyclohexanone and a number of aldehydes (Table 1.8.4.18).

1 Entry R H2O:139a Anti/Syn Product Yield [%] ee [%]

1 4-NO2C6H4 1:1 11:1 129a, 62 96

2 4-NO2C6H4 2:1 10:1 129a, 65 95

3 4-NO2C6H4 3:1 9:1 129a, 66 93

4 4-CNC6H4 2:1 6:1 129d, 65 93

6 Cl-C6H4 2:1 7:1 129f, 57 92

5 Br-C6H4 2:1 6:1 129j, 53 89

8 4-CO2MeC6H4 2:1 5:1 129e, 70 94

8 2-Naphthyl 2:1 8:1 129h, 45 90

Table 1.8.4.18. Investigation of water tolerance of the catalyst 70

The aldol reaction was water tolerant (water/cyclohexanone, v/v, 1:1 to 1:3) (Table 1.8.4.18), however, with slight decrease in both activity and stereoselectivity. The decreasing trend became slightly more pronounced when more water was included in the reaction system (entries 1-3).

The cooperative nature of this catalytic system was revealed by the fact that the ligand alone could not catalyze the aldol reaction between cyclohexanone and 4- nitrobenzaldehyde. All the reactions of cyclohexanone predominantly generated the anti aldol product with (2S, 1’R) configuration. The mechanism is likely to follow that the metal coordinates with the chelating ligand to form a rigid chiral structure and acts as a Lewis acid to activate the aldehyde; the primary amine reacts with cyclohexanone to form an enamine attacking the activated aldehyde from the re–face to generate the product figure.

In summary, this new class of primary amine-metal Lewis acid cooperative bifunctional catalysts based on simple bidentate ligands displayed high activity in the direct asymmetric aldol reactions of ketones with both electron–rich and electron–poor aldehydes. The enantioselectivities obtained from these reactions are comparably with those catalyzed by the best organocatalysts, and are much higher than those of tridentate ligand system. It is notable that these catalysts possess both the advantages of metal Lewis acids and organocatalysts, requiring low catalytic loading and being water tolerant.

1.8.5 Catalyst based on bidentate secondary amine ligand system: metal– Lewis acid promoted highly stereoselective formation of cyclic aminals from aldehydes. Following successful designs and applications of the bidentate primary amine ligand and tridentate secondary amine ligand systems in our previous investigations157,172, we explored another bidentate ligand system but based on secondary amine. The ligand was synthesized from a coupling reaction between 2- aminopyridine and its derivatives with N-protected proline followed by deprotection (Scheme1.8.5.41).

The same protocol was applied to the syntheses of other secondary amine ligands 142 and 143

Catalytic exploration began with the aldol reaction between acetone and 4– nitrobenzaldehyde under neat condition using different metal salts as Lewis acids (Table 1.8.5.19).

Entry Metal Time[h] Yield[%] ee[%]

1 Cu(OTf)2 72 43 71

2 Cu(NO3)2 48 trace -

3 Cu(OAc)2 72 34 5

4 Cu(SbF6)2 48 56 60

5 Ni(ClO4)2 72 49 42

6 Zn(ClO4)2 48 45 38

7 Zn(OAc)2 24 85 56

8 Co(OAc)2 72 53 11

9 Co(ClO4)2 48 84 30 Table 1.8.5.19. Screening of metals with 140

Metal screening showed moderate results with the best enantioselectivity observed

(71% ee) when Cu(OTf)2 is used, but the yield was low 43% (Table 1.8.5.19, entry

1). Zn(OAc)2 furnished the best combination of yield 85% and enantioselectivity

56% ee (entry 7). While the use of Co(ClO4)2 gave somewhat higher yield (84%) but the selectivity was low (30% ee, entry 9). The use of Cu(SbF6)2 which was proved to be the best condition in our previous investigations, gave moderate results (56% yield, 60% ee, entry 4).

Using the best metal salt (Zn(OAc)2) from Table 1.8.5.19 to catalyze the aldol reaction between acetone and 4-nitrobenzaldehyde, different solvents were screened and the results are tabulated in Table 1.8.5.20. 73

Entry Metal Time[h] Yield[%] ee[%] 1 DMF 72 53 27 2 DMSO 72 45 28

3 CH3CN 48 71 47 4 THF 72 62 50 5 EtOH 24 47 15 6 MeOH 24 95 45

7 CHCl3 5days 48 12 8 DCM 5days 71 45 9 Toluene 72 52 42 10a neat 72 63 46 11b neat 72 49 20

Table 1.8.5.20. Solvent screening with 140/Zn(OAc)2. [a] using ligand 142. [b] using ligand 143

As shown in the table, some solvents like methanol and acetonitrile were appreciably active delivering as high as 95% and 71% yield, but the enantioselectivities were low (45% and 47% ee, respectively, Table 1.8.5.20, entries 3, and 6). In general, even though some solvents gave good yields, the enantioselectivities were low for the solvents screened. When other ligands 142 and 143 were used, both activity and enantioselectivities were still low (entries 10

and 11). During this process we discovered that apart from the expected aldol adduct 118a, there was another major product which was identified as cyclic aminal 144 (Scheme 1.8.5.42).

Cyclic aminals and compounds of similar structure constitute a widespread structural motif in natural products and pharmaceuticals.183--188 Chiral cyclic aminals have also been used as chiral auxiliaries,189 and more recently as chiral organo catalyst in asymmetric synthesis.190--195 Possibly due to their instability under acidic, basic and other harsh conditions, only a limited number of aminal forming reactions have been reported,196-206 the stereoselective synthetic routes to these compounds are even rare. Very recently, the Antilla group developed the syntheses of acyclic aminals and hemiaminals through chiral phosphoric acid catalyzed asymmetric addition of amides and alcohols to imines.207 The List group has also discovered a new highly enantioselective direct synthesis of cyclic aminals from aldehyde and 2-aminobenzamide catalyzed by a new chiral phosphoric acid catalyst.208

When 40 mol% of L-proline-modified catalyst 140 in conjunction with 20 mol%

Cu(NO3)2 was used to catalyze the aldol reaction of 4-nitrobenzaldehyde with acetone, along with the aldol addition product 118a, cyclic aminal 144a was also isolated in reasonable yield. Only one diastereomer was detected in the reaction. The identification of 144a was determined by 1H NMR, 13C NMR, COSY and MS. We rationalize this reaction as cyclization reaction of 140 with 4- nitrobenzaldehyde to form 5-membered cyclic aminal 144a.

Interestingly, no cyclization reaction occurred between acetone and 140, even though large excess of acetone was used as both a reactant and the solvent.

Figure 1.8.5.16. H1NMR of the reaction mixture for the cyclization reaction. Top: with Cu(NO3)2; bottom: without metal

We then started out to examine if this side reaction can be generalized. A model reaction between 140 and 4-nitrobenzaldehyde to furnish cyclic aminal 144a was initially established. After optimizing the reaction condition, a clean reaction occurred in refluxing ethanol overnight in the presence of 30 mol% of Cu(NO3)2 furnishing only one pure diastereomer 144a in 58% yield. It was discovered that this reaction can also occur without metal catalyst under similar conditions. In sharp contrast to the reaction carried out with Cu(NO3)2, two diastereomers were isolated in a dr ratio of 1:1 (144a /145a). These two diastereomers were separated using flash chromatography on Silica and characterized. Fig 1.8.5.16 shows the 1H

NMRs of the reaction mixture for the reaction in the presence of Cu (NO3)2 (top) and without metal (bottom). The relative configuration of the two diastereomers (144a and 145a) was assigned by NOESY. Strong NOEs were observed for the cis-isomer 145a (Fig. 1.8.5.17) between H1 and H2, and the two Hs at carbon 3 and the H at carbon 4; no NOE were observed for the trans-isomer 144a between the above mentioned protons; NOE was observed for 144a between H2 and protons at carbon 3, on the contrary, no observation of NOE for 145a for the corresponding protons. The one diastereomer obtained from the cyclization reaction in the presence of Cu(NO3)2 was identified as trans-isomer 144a (Fig. 1.8.5.17).

Screening of different metals and different Cu(II) salt at different loading was carried out (Table 1.8.5.21). Not to our surprise, all metal salts (Cu(II), Zn(II), Co(II), and Ni (II)) showed the stereo-directing capability leading to essentially only trans-isomer 144a in various yields. However, all the Cu(II) salts (entries 1, 2, 3, and 4) showed similar results in terms of yield. It is also found that the amount of loadings of the Cu(II) salt affects the yield of the reaction. As shown in entries 3, 4, 8, and 9, the less the Cu(II) salt was used, the better the yield was obtained. At

10 mol% loading of Cu(OTf)2, as high as 87% yield was achieved with/without the inclusion of molecular sieves.

Entry Lewis Acid Cat.[mol-%] Yield[%] dr [144a/145a]

1 Cu(NO3)2 30 58 (144a) >99/1

2 CuCl2 30 60 (144a) >99/1

3 Cu(OTf)2 30 60 (144a) >99/1

4 Cu(ClO4)2 30 57 (144a) >99/1 34(144a) 1/1 5 No catalyst ~ 33 (145a) 20 (144a) 1/3 6[a] No catalyst ~ 49 (145a)

[a] 7 Cu(OTf)2 10 49 (144a) >99/1

8 Cu(OTf)2 10 87 (144a) >99/1

[b] 9 Cu(OTf)2 10 86 (144a) >99/1

10 Ni(ClO4)2 10 44 (144a) >99/1

11 Co(ClO4)2 10 50 (144a) >99/1

12 Zn(ClO4)2 10 44 (144a) >99/1 Table 1.8.5. 21. Metal screening for the formation of cyclic aminals. [a] rt, [b] 150mg molecular sieves were added.

Having identified Cu(II) salts as a suitable stereo-director and/or catalyst, we chose

Cu(OTf)2 (10 mol%) as the metal catalyst, and reacted with different aldehydes with 140 (Table 1.8.5.22). All the aromatic aldehydes generated the expected cyclic trans aminals as the only diastereomer, no cis-isomer was detected on either TLC or 1H NMR.

Nitro aromatic aldehydes tend to give higher yields than the more electron-rich aldehydes with highest yield of 87% obtained for 4-nitrobenzaldehyde and lowest yield of 44% obtained for 4-methylbenzaldehyde.

Entry R Product Yield [%] dr [144/145]

1 4-NO2C6H4 144a 87 >99/1

2 3-NO2C6H4 144b 64 >99/1

3 2-NO2C6H4 144c 70 >99/1

4 4-CNC6H4 144d 51 >99/1

5 4-ClC6H4 144e 45 >99/1

6 C6H5 144f 48 >99/1

7 4-MeC6H4 144g 44 >99/1 Table 1.8.5.22. Aldehyde scope with substrate 140.

We also explored the cyclization reaction of N-phenyl substituted proline amide

148 with different aldehydes (Table 1.8.5.23) in the presence of Cu(OTf)2. Interestingly, without the coordinating N-pyridyl substitute on proline amide, 148

also reacted with all the aldehydes giving cyclic trans-aminals 146 as the only one diastereomer produced in the reactions. Again, more electron-poor aromatic aldehydes tend to give higher yields relative to the more electron-rich aldehydes. Similar to proline amide 144, when 148 was reacted with 4-nitrobenzaldehyde without Cu(OTf)2, two diastereomers (146a and 147a) were isolated in 5:1 molar ratio.

Entry R Product Yield [%] dr [146/147]

1 4-NO2C6H4 146a 65 >99/1

2 3-NO2C6H4 146b 68 >99/1

3 2-NO2C6H4 146c 65 >99/1

4 4-ClC6H4 146d 34 >99/1

5 C6H5 146e 41 >99/1 a d 6 4-NO2C6H4 146a/147a 62 5/1 b d 7 4-NO2C6H4 146a/147a 23 1/2 c d 8 4-NO2C6H4 146a/147a 19 1/2

Table 1.8.5.23. Aldehyde scope with (S)-N-phenylpyrrolidine-2-carboxamide 148, [a] reaction carried out without Cu(OTf)2, [b] reaction carried out at rt without Cu(OTf)2, [c] reaction carried at rt, [d] combined yield. In order to figure out the roles that the metal plays, we also carried out the reactions of amide 140 with 4-nitrobenzaldehyde at room temperature with and without Cu(OTf)2. Both of the reactions (Table 1.8.5.21, entries 6 & 7) occurred at 81

room temperature after 3 days, but without complete conversion. The reaction with

Cu(OTf)2 still gave only one diastereomer 144a in 49% yield; interestingly, the reaction without Cu(OTf)2 gave two diastereomers with 145a as the major product (144a /145a, 1/3). Both of the reactions of amide 148 with 4-nitrobenzaldehyde at room temperature with and without the inclusion of Cu(OTf)2 gave a 1/2 ratio of 146a/147a (Table 1.8.5.23, entries 7 and 8), noting a reverse ratio of 1/5 for

147a/146a was obtained at higher temperature in the absence of Cu(OTf)2. It appears that Cu(OTf)2 participated in the reaction of 140 with 4-nitrobenzaldehyde at room temperature, but was not apparently involved in the reaction of 148 with 4- nitrobenzaldehyde at room temperature. These results indicate clearly that the metal assumes a structural role in these reactions, the involvement of which helps form the thermodynamically more stable trans-products. Even though it is not clear how the metal was involved in the reaction of 148 with aldehydes, we have proposed a mechanism for the reaction of N-(pyridin-2-yl)-proline amide 140 with aldehydes (Fig. 1.8.5.18). The reaction mechanism is likely to follow the addition of amide to the iminium ion formed in situ. We speculate that the Cu (II) salt may play dual roles in this cyclization reaction: to induce the stereoselectivity.

In summary, we have discovered that metal Lewis acid can promote a highly diastereoselective cyclization reaction of N-monosubstituted proline amide with aldehyde to form interesting cyclic aminals. In addition to the above mentioned medicinal and catalytic applications, this highly diastereo-selective reaction may also be very useful in retro-inverse mimics.

1.8.6. Direct asymmetric aldol reaction of ketones

Asymmetric variants of the aldol reaction involving aldehydes as acceptors with ketones, esters and their derivatives have been studied intensively since the rebirth of organocatalysis in 2000. On the other hand, un-activated ketone–ketone condensation has remained a challenge for a long time, partly due to their inherent inactivity and the retro-aldol reaction.209 Asymmetric aldol reaction of simple ketones generating tertiary carbon centers are very enticing due to their potentials in drug development, and yet very challenging. The attenuated reactivity is one factor that has limited the exploration of this protocol as a way of building complex structures. To some extent, activating the acceptor or donor via chelation, silylation and having an electron withdrawing group next to the reaction center seems to have partially solved the problem. 210,211 These activation methods shift the equilibrium of the reaction to lie on to the right thereby making the cross aldol addition of ketone possible.212 Another feature that has made cross aldol addition of ketone challenging is the presence of two sterically bulky groups flanking the carbonyl group as compared to aldehydes. This feature has made enantiofacial discrimination relatively challenging even though a few groups have carried out metal catalyzed aldol addition of ketones.213-222 Even though the above solution has resulted into a clear demonstration of the principle and possibilities of carrying out ketone-ketone aldol reaction they surfer from very narrow substrate scope and usually require special handling techniques during the transformations.

Based on the results obtained so far, it can be concluded that the catalysts have to strongly activate the substrates, and, at the same time, are able to effectively do enantiofacial discrimination in order to achieve ketone-ketone aldol addition. Our catalyst design seems to fit these requirements perfectly. In principle if we switch

from moderate Lewis acid like Cu(II) to much stronger ones like La(III) we should be able to carry out the transformation.

Discussion and Results

1.8.6.1 Direct asymmetric aldol reactions to un-activated ketones

The investigation of our cross aldol reaction of ketones started when we attempted to carry out an aminoxylation of ketones using nitroso benzene (Scheme 1.8.6.1.43).

To our surprise our target molecule A was not isolated, only a double α- aminoxylation and a self-addition product of cyclohexanone was obtained in about 5mg. We then became interested in investigating the self-addition reaction further. After we conducted a series of experiments we found out that the self aldol reaction did not require the presence of nitrosobenzene. We then screened a number of metals using ligand 139a and 140 and the results are tabulated in Table 1.8.6.1.24.

Entry Ligand Metal Yield[mg]

1 140 Cu(SbF6)2 7

2 140 Cu(SbF6)2 12

3 140 La(OTF)2 17

4 140 Y(OTF)2 10

5 140 Yb(OTF)2 8.2

6 140 Sc(OTF)2 14

7 140 Sm(OTF)2 15

8 140 Co(ClO4)2 9.3

9 139a Sm(OTF)2 10 Table 1.8.6.1.24. Metal screening for self aldol reaction of cyclohexanone.

The secondary amine based ligand gave a better yield compared to the primary based ligand (Table 1.8.6.1.24, entries 1 and 2). We then checked other metals especially strong Lewis acids because we had hoped that strong activation of the donor might be the key to increasing the yield. To our disappointment all the metals screened furnished low yield. Comparably, La(OTf)2 gave us slightly more product but that only represented a 7% yield (entry 3).

Using the best conditions from Table 1.8.6.1.24), La(OTf)2 and 140 we screened some solvents (Table 1.8.6.1.25).

Entry Metal Solvent:[0.5mL/0.5mL] Yield[mg]

1 La(OTf)2 DMF 3

2 La(OTf)2 DMSO 3

3 La(OTf)2 MeCN 6

4 La(OTf)2 DCM 5

5 La(OTf)2 THF 13

6 Sm(OTf)2 THF 9

8 Sc(OTf)2 THF 8

Table 1.8.6.1.25.Solvent screening for self aldol reaction of cyclohexanone.

The results still showed low conversions of cyclohexanone, with THF/ La(OTf)2 combination furnishing the best results with only 13mg of the product. (Table

1.8.6.1.25, entry 5). When THF was applied with Sm(OTf)2 and Sc(OTf)2 (entries

6 and 7) the yields were still lower than those acquired when La(OTf)2 was used.

In all our investigations we were using the reactants very much in excess, so we decided to carry out a stoichiometric reaction using THF as the solvent and 20 mol% of the catalyst based on cyclohexanone. After 3days we only got 4mg of the product which was <5% yield.

After obtaining all these disappointing results, we decided a cross aldol reaction of cyclohexanone and acetophenone, (Scheme 1.8.6.1.44) and cyclohexanone and acetone (Scheme 1.8.6.1.45), hoping they could be better alternatives. The intrinsic differences in reactivity of these ketones will discriminately assign one as the acceptor and the other as the donor.

As shown in Scheme 1.8.6.1.44, after 3 days we were able to isolate two products 152 in 8% yield and 150 in 3% yield. Surprisingly, neither could we detect any self aldol reaction of acetophenone nor the cross aldol in which cyclohexanone was the donor to acetophenone. In the case of acetone and cyclohexanone (Scheme 1.8.6.1.45) we got 14% of the cross aldol addition product 153 and 2% self- addition product 150. Again we did not observe any product from self-addition of acetone. Unfortunately, the attempt to optimize the reaction conditions in both 88

situations including the use of either the donor or acceptor as a limiting reagent, using different ratios of the reactants, using different solvents and mixture solvents with different ratios and using different metals was proved unsuccessful. Other ketones were also investigated in cross aldol reactions (Table 1.8.6.1.26).

Table 1.8.6.1.26 .Exploration of the crossed aldol reaction of inactivated ketones. The ketones explored (Table 1.8.6.1.26) either did not react or the TLC showed a complex mixture that was not separable. However, a reaction between cyclohexanone and methylvinylketone (MVK) did not give an aldol product but a Michael adduct (Table 1.8.6.1.26, entry 5). Further optimization of the reaction conditions using La(OTf)3/ligand 139a gave the best yield of 30%.

In summary, even though the yields are low in all the reactions, we were able to get the expected products. The principle and the attainability of our catalysts to catalyze the direct aldol reaction of un-activated ketones have been demonstrated. Further screening of ligands and using much stronger Lewis acids such as Ti(IV) and Al(III) to activate the substrate might help. Other conditions such as temperature, additives and solvents deserve further exploration.

1.8.6.2 Direct Asymmetric Aldol Reactions to Activated Ketones

We then decided to involve activated ketone acceptors with the hope to improve the turnover of our catalysts. Different ketone combinations were explored (Table 1.8.6.2. 27).

When moderately activated ketones were used (Table1.8.6.2.27, entries 1,2 and 3) no product was formed even after screening different conditions such as solvents,

metals and ligands. On the other hand, the more activated ketones easily furnished the expected products (entries 4, 5, 6, 7and 8). These were then subjected to further investigations to optimize the conditions.

1.8.6.2.1. Direct asymmetric aldol condensation of isatin and acetone

We started our screening by employing some of the best conditions that we have developed in our previous investigations. We therefore used ligands 123, 139a and

140 (Fig.1.8.6.2.1.18) with Cu(SbF6)2. We then screened other metals and some solvents (Table1.8.6.2.1.28).

Entry Metal Ligand Solvent Conversion[%] ee [%]

1 Cu(SbF6)2 139a neat 100 0

2 Cu(SbF6)2 140 neat 100 28

3 Cu(SbF6)2 123 neat 100 0

3 Co(ClO4)2 140 neat 100 21

4 Ni(ClO4)2 140 neat 100 28

5 In(OTf)3 140 neat 40 42

6 Zn(OTf)2 140 neat 100 16

7 Y(OTf)3 140 neat 100 0

9 Cu(SbF6)2 140 Methanol 100 38

10 Cu(SbF6)2 140 THF 100 18

11 Cu(SbF6)2 139a Methanol 100 0

12 Cu(SbF6)2 139a THF 100 0

Table 1.8.6.2.1.28. Metal screening of the aldol reaction between isatin (limiting) and acetone.

All three ligands chosen with Cu(SbF6)2 in neat conditions demonstrated high activity as they furnished the product in less than 24 hours with 100% conversion (Table1.8.6.2.1.28, entries 1,2 and 3), ligand 123 and 139a did not show any enantioselectivity (entries 1 and 3). Ligand 140 showed lower selectivity giving 28% ee (entry 2). We then subjected ligand 140 to different metals under neat conditions. Apart from In(III), all the other metals showed high activity. Y(III) gave a racemate (entry 7), while Co(II), Ni(II) and Zn(II) gave 21%, 28% and 16% ee respectively (entries 3,4 and 6). In(OTf)3 showed very low activity affording only 40% conversion after 24 hours, albeit with slightly higher enantioselectivity (42% ee (entry 5).

1.8.6.2.2 Direct asymmetric aldol reaction of isatin and (E)-4-phenylbut-3-en- 2-one

We started our investigation of the reaction between isatin and 156 (Scheme 1.8.6.2.2.46) using ligand 139a.and 140. After 24 hours, both ligands furnished the aldol addition product 40% and 50% yields, respectively. Both ligands gave a hetero–Diels Alder (HDA) product along with the aldol products. We then switched to much stronger Lewis acid La(OTf)3. More HDA product was obtained but the yield was still low 10%. We then screened different solvents using ligand

140 and La(OTf)3 (Table 1.8.6.2.2.29).

Entry Solvent HDA(157)/Aldol(158)

1 MeCN 1:3

2 MeOH 1:3

3 Isopropanol 1:5

4 DMSO ~

5 Toluene 1:4

6 DCM 1:5

8 DMF ~

Table.1.8.6.2.2.29. Solvent screening for HDA reaction.

Most of the solvents surveyed gave aldol product as the major product and HDA product as the minor one (Table 1.8.6.2.2.29, entries 1, 2, 3, 5 and 6). DMSO and DMF however, furnished only the aldol products (entries 4 and 8). Even when we screened other strong Lewis acids like Sm(OTf)3 Sc(OTf)3 Sm(OTf)3 Yb(OTf)3 and

Y(OTf)3, more aldol product was still obtained compared to HDA product.

We then decided to extend our ligand repertoire by synthesizing ligand 160, (Scheme 1.8.6.2.2.47). Two 2-(methyl amino) pyridine ligand derivatives were also made utilizing the same protocol as for ligand 162 and 162.

These three ligands were then tried in the HDA reaction (Table 1.8.6.2.2.30).

Entry Ligand Metal Solvent HDA/Aldol

1 160 La(OTf)3 THF ~

2 160 Y(OTf)3 THF ~

3 162 La(OTf)3 THF 2:1

4 162 Sm(OTf)3 THF 1:1

5 162 Sc(OTf)3 THF 1:1

6 162 Yb(OTf)3 THF 1:1

7 162 Cu(SbF6)2 THF ~

8 162 Y(OTf)3 THF 1:1

9 162 InCl3 THF 1:1

10 162 La(OTf)3 MeCN 3:1

12 162 La(OTf)3 DMSO ~

13 162 La(OTf)3 Isopropanol 2:1

14 162 La(OTf)3 DCM 1:4

15 162 La(OTf)3 DMF ~ Table 1.8.6.2.2.30. Investigation of other ligands and other conditions.

Ligand 160 was not active when used in combination with La(OTf)3 or Y(OTf)3 it did not give neither the desired HDA nor the aldol products (Table 1.8.6.2.2.30, entries 1 and 2). When we switched to ligand 162 and screened various metals in THF (entries 3-6), we started seeing more of the HDA than the aldol products with

La(OTf)3 giving the best ratio of 2:1, (entry 3.). MeCN turned out to be the best solvent in combination with La(OTf)3 and 162 furnishing HDA and aldol product in 3:1 ratio (entry 10). Polar aprotic solvents like DMSO and DMF did not furnish any known product (entries 12 and 15). Even if the regioselectivity of these reactions for HDA products improved, the activity was still low. The reactions went for five days without completion.

When ligand 161 was tried in THF with different metals, the chemoselectivity of the reaction increased significantly. In the presence of Y(OTf)3, up to 8:1 of HDA/aldol ratio was obtained (Table 1.8.6.2.2.31, entry 5). All the metals tested performed moderately with La(OTf)3 giving the lowest HDA/aldol ratio of 1:1 (entry1). The metals that performed well in THF were further investigated with other solvents (entries, 10-17) but none gave a better result than THF. In DMF and DMSO only the aldol product was formed.

Entry Ligand Metal Solvent HDA/Aldol

1 161 La(OTf)3 THF 1:1

2 161 InCl3 THF 5:1

4 161 Sm(OTf)3 THF 4:1

5 161 Y(OTf)3 THF 8:1

6 161 Yb(OTf)3 THF 4:1

9 161 Sc(OTf)3 THF 2:1

10 161 Y(OTf)3 MeCN 3:1

11 161 Y(OTf)3 MeOH 2:1

12 161 Sm(OTf)3 DCM 5:1

13 161 Sm(OTf)3 MeOH 3:1

14 161 Sm(OTf)3 MeCN 2:1

15 161 InCl3 MeCN 2:1

16 161 InCl3 DCM 3:1

17 161 InCl3 MeOH 1:1 Table 1.8.6.2.2.31. Screening of more conditions using ligand 161. 100

We then decided to investigate the effect of stoichiometry on the reaction (Table1.8.6.2.2.32).

Entry Donor/Acceptor[eqv] HDA/Aldol HDA[Yield(%)] Ee[%]

1 2:1 6:1 24 44

2 6:1 2:1 20 40

3 10:1 1:1 17 30

4 20:1 1:2 20 11

5 1:2 <1:99 ~ ~

6 1:6 ~ ~ ~

7 1:10 ~ ~ ~

Table. 1.8.6.2.2.32. Investigation of the stoichiometry of the HDA reaction.

Increasing the amount of the donor showed an increase in activity but a decrease in enantioselectivity (Table 1.8.6.2.2.32, entries 1-4). The donor increment also resulted into a reduction in the HDA product. The HDA product became the minor product when the amount of the donor was increased to 20 equivalents of (entry 4). Increasing the acceptor had an adverse effect on activity (entries 5-7). Addition of only 2 equivalents of the acceptor caused the reaction much slow furnishing mostly

101

aldol product (entry 5). Add more acceptor to the reaction mixture led to no reaction (entries 6 and 7). All these reactions investigated never went to completion even after 5days. We then decided to change the acceptor from isatin to more active 5–nitroisatin. With this acceptor, the reaction went to completion in 4days giving the HDA and aldol products in 1:1 ratio with a little bit dehydrated aldol product (confirmed with MS). X –ray crystals structure of the HDA product was solved by Dr. Christopher Ziegler group at University of Akron (Fig. 1.8.6.2.2.19).

Figure 1.8.6.2.2.19. X-ray crystal structure of HDA product of 5-nitroisatin and (E)-4-phenylbut-3-en-2-one. All the reactions that were performed gave low yields with the best being 22% after 5 days. A closer analysis of the TLC revealed that some compounds always remained on the baseline that could not be isolated and identified. We then decided 102

to add 1,1,1,3,3,3-hexafloro-2-propanol (HFIP) as an additive. HFIP has been shown to be an excellent additive in a number of transformations that assist in the dissociation of the catalyst to enhance turn over.223-225 Unfortunately, the addition of the additive did not seem to reduce the amount of unidentified materials on the baseline of the TLC. We speculate that the presence of multiple atoms on isatin that can coordinate to the metal Lewis acid might have made the reacting systems very complicated. We therefore prepared N-methyl and N-benzyl protected isatin (Scheme 1.8.6.2.2.48).

When we applied the methyl protected isatin 163 to the reaction, activity of the reaction became low giving a 1:1 ratio of HDA/aldol products, and the unidentified material on the baseline still remained. Changing to benzyl protected isatin 164 did not improve the situation, making the reaction even much slower with aldol being the major product.

We wanted to know whether the formation of the HDA product was stepwise in which the aldol product was formed first followed by cyclization to the HDA product, or a concerted transformation without involving the aldol product. If the 103

mechanism of generating the HDA product was stepwise with the formation of the aldol product first, then in principle we should be able to convert the aldol product to HDA product in the presence of our catalyst (Scheme 1.6.2.2.49). As it turned out, after 3days only the dehydrated product 165 was obtained; HDA product was not observed on TLC and NMR spectra, MS showed a little peak for HDA product.

In conclusion, using our catalyst system we were able to carry out a hetero–Diels

Alder reaction and an aldol reaction between isatin and (E)-4-phenylbut-3-en-2- one. In addition the direct aldol reaction of isatin and acetone was also demonstrated. Spirol–oxidoles are an interesting structural moiety found in a number of natural products possessing unprecedented biological activities.225,226 For this reason, they have attracted attention from the synthetic organic chemists.227 Even if the yields and stereoselectivities are not impressive, the fact that the product was realized through a possible HDA reaction serves good starting point for further investigation.

104

Experimental for 1.8.1 and 1.8.2

(2S,2’S)-N,N'-([2,2'-Bipyridine]-6,6'-diyl)bis(pyrrolidine-2-carboxamid (117)

800 mg (3.2mmol) of Cbz–protected proline, 0.5 mL of TEA and 25mL of THF were charged in a 50mL flask and chilled to 0 oC in ice bath to which 30µL of ethylchloroformate was added drop wise. The mixture was allowed to warm up to room temperature and stirred for 6h. 250mg (1.4mmol) of [2, 2'-bipyridine]-6,6'- diamine was added in one portion. The resulting mixture was stirred overnight at room temperature and was then heated to reflux for additional 6h. The reaction mixture was filtered, and the solvent was removed under vacuum. The oily product was dissolved in DCM and was washed three times with sodium bicarbonate followed with water. The resulting residue was purified by column chromatography (DCM:MeOH, v:v,10:1) to afford a white solid 116 (517mg). The solid was then charged in a schlenk flask equipped with methanol (20mL), 10% Pd/C (70mg) and hydrogen, and the resulting mixture was stirred overnight. The Pd catalyst was then filtered off through a pad of cilite and the solvent was removed under reduced pressure to give a white solid (240 mg 45%).

1 H –NMR (500 MHz, CDCl3), δ: 1.78-1.81 (m, 7H), 2.02-2.07 (m, 3H), 2.22-2.25 (m, 2H), 3.07-3.12 (m, 4H), 3.90-3.95 (m, 2H), 7.78-7.81 (t, 2H), 8.06 (d, J= 5Hz), 8.26 (d, J = 10Hz), 10.18 (s, 2H)

13 C NMR(125Hz, CDCl3) δ 30.91, 39.87, 47.43, 61.11, 113.75, 113.93, 116.77, 117.04, 139.12, 139.24, 150.76, 151.11, 153.88, 153.94, 174.55, 177.21; MS (ESI) + C20H24N6O2, [M+H] 381.20

105

(S)-N-(6'-pivalamido-[2,2'-bipyridin]-6-yl)pyrrolidine-2-carboxamide (120)

200 mg (1.071mmol) of [2,2'-bipyridine]-6,6'-diamine, 1 mL TEA and 20mL of DCM were charged in a 50mL flask and was chilled to 0 oC in ice bath to which 132µ L (1.076mmol) of pivaloyl chloride was added drop wise. The solution was allowed to warm up to room temperature and stirred overnight then refluxed for additional 6h. The mixture was then filtered, and solvent removed in vacou. The oily product was dissolved in DCM then washed three times with sodium bicarbonate followed with water then purified by column chromatography (DCM:MeOH, v:v, 10:1) to afford a mono coupled intermediate as a colorless oil N-(6'-amino-[2,2'-bipyridin]-6-yl) pivalamide, A (230mg). Cbz–protected proline (390 mg (1.57mmol), 2 mL of TEA and 40mL of THF were charged in a 100mL flask and chilled to 0 oC in ice bath. After which 149µL (1.57mmol) of ethylchloroformate was added drop wise. The solution was allowed to warm up to room temperature and a stirred for 6h. 141mg (0.522mmol) of N-(6'-amino-[2,2'- bipyridin]-6-yl)pivalamide (A) was added in one portion and stirred overnight then refluxed for additional 6h. The mixture was then filtered, and the solvent was removed in vacou. The oily product was dissolved in DCM then washed three times with sodium bicarbonate followed with water then purified by column chromatography (DCM:MeOH, v:v, 30:1) to obtain a white solid (187mg). The solid was then charged in a schlenk flask equipped with methanol 15mlL, 10% Pd/C (30mg) and hydrogen and stirred overnight. The catalyst was then filtered 106

through celite and the solvent was removed in under reduced pressure to afford a white solid (113mg) 120 Yield 80%.

1 H NMR (500 MHz, CDCl3) δ 1.28(s, 9H), 1.75-1.80 (m, 2H), 2.01-2.07 (m, 2H), 2.19-2.25 (m, 1H), 3.04-3.10 (m, 2H), 3.87-3.89 (m, 1H), 7.78-7.81 (t, 2H), 7.99- 13 8.08(m, 3H),8.24-8.28(m, 2H), 10.20 (s, 1H); C NMR(125Hz, CDCl3) δ 26.30, 27.57, 30.91, 39.87, 47.43, 61.11, 113.75, 113.93, 116.77, 117.04, 139.12, 139.24, 150.76, 151.11, 153.88, 153.94, 174.55, 177.21; MS (ESI) 366.1 (M-H)-

(2R,2'S)-N,N'-(pyridine-2,6-diyl)bis(pyrrolidine-2-carboxamide)1 122

N-carbobenzyloxyl-L-Proline (10.96 g, 44 mmol) was dissolved in THF (100 mL). The solution was cooled down to 0 oC. TEA (6.2 mL, 44 mmol) was added. To this solution ethylchloroformate (4.8 g, 44 mmol) was added drop wise in 15 minutes. The reaction mixture was stirred at 0oC for 45 min, then amine (2.18 g, 20 mmol) in 30 mL THF was added slowly in a period of 10 minutes at 0oC. The resulting solution was stirred at room temperature for 16 h, and then refluxed for 4 h. After cooling down to room temperature, the solid was filtered off and then solvent was removed. The crude solid product was taken into DCM, and was washed with aqueous NaHCO3 and dried with anhydrous Na2SO4. After removal of the solvent, the residue was purified through column chromatography on silica gel (eluent: DCM:ethyl acetate, v:v, 2:1) to give A ( 6.0 g) 107

The obtained N-Cbz compound B (6.0 g), 10% Pd/C (1.5 g), methanol (80 mL) were mixed in a 150 mL two-neck flask and stirred under hydrogen (1 atom) for 4 h. The solution was filtered on Celite to remove the Pd/C, and then evaporated to 25 dryness to give the products 122 (2.7g): Yield 85% ; [α]D = +12.0 (c= 0.13,

CHCl3);

1 H NMR (500 MHz, CDCl3) δ 1.72-1.76 (m, 4H), 1.97-2.01 (m, 2H), 2.16-2.20 (m, 4H), 2.97-3.06(m, 4H), 3.81-3.84(m, 2H), 7.65(t, J = 8 Hz, 1H), 7.91(d, J = 8 Hz, 13 2H), 9.93 (s, 2H); C NMR(125Hz, CDCl3) δ 26.20, 30.76, 47.31, 61.02, 108.96, 140.41, 149.41, 174.12; MS (ESI) 326.2 (M+Na)+

tert-butyl((S)-3-methyl-1-oxo-1-((6-((S)-pyrrolidine-2-carboxamido)pyridin-2- yl)amino)butan-2-yl)carbamate (123)

To a stirring solution of N-Boc-L-valine (2.17g, 10 mmol) in CH2Cl2 (100 mL) was added pyridine-2,6-diamine (10 mmol, 1.09g), DCC (2.3g, 10 mmol), HOBt (1.5g, 10 mmol) and DIPEA (1.25 mL, 10 mmol) at 0oC and then reaction mixture was stirred at room temperature for 24h. The reaction was filtered and washed with aqueous NaHCO3. The organic phase was evaporated under reduced pressure and purified by column chromatography (silica gel) to give the pure product B (1.43 g, 46%).

N-carbobenzyloxyl-L-Proline (1.58 g, 6.3 mmol) was dissolved in THF (20 mL). The solution was cooled down to 0oC. TEA (0.875mL, 6.3 mmol) was added. Then 108

to this solution ethylchloroformate (0.6 mL, 6.3mmol) was added drop wise for 15 min. After the solution was stirred at 0oC for 45 min, amine B(1.3g, 4.2mmol) was added slowly for 10 minutes in 10mL THF solution at 0oC. The resulting solution was stirred at room temperature for 16h, and then refluxed for 3h. After cooling down to room temperature, the reaction mixture was filtered off and the solvent removed to give a solid that was dissolved in DCM. The DCM solution was washed with aqueous NaHCO3 and dried with anhydrous Na2SO4. After removal of the solvent, the residue was purified through column chromatography on silica gel (eluent: DCM: ethyl acetate v/v, 20/1) to give a white solid (1.35g, yield: 60%)

The obtained N-Cbz compound (1.35g), 10% Pd/C (300mg), methanol (30mL) were mixed in a 100mL two-neck flask and stirred under hydrogen (1 atom) for 4 h. The solution was filtered on Celite to remove the Pd/C, and then evaporated to 25 dryness to give the product 123 (0.91g, yield: 93%). [α]D = 4.2 (c=1.45 CHCl3);

1 H NMR (500 MHz, CDCl3) δ 0.96 (d, J = 6.5 Hz, 3H), 1.00 (d, J = 6.5 Hz, 3H), 1.43 (s, 9H), 1.73-1.77 (m, 3H), 1.99-2.01(m, 1H), 2.20-2.23(m, 2H), 3.04-3.09(m, 2H), 3.83-3.86(m, 1H), 4.09(m, 1H), 5.16(br, 1H), 7.62-7.64(m, 1H), 7.79(m, 1H), 13 7.89-7.91(m, 1H), 8.22(m, 1H), 9.90(br, 1H); C NMR(125Hz, CDCl3) δ 18.00, 19.25, 25.98, 28.30, 30.65, 30.96, 47.14, 61.07, 80.08, 109.09, 109.24, 140.10, 149.09, 149.12, 156.32, 170.82, 173.31, 175.09; MS (ESI) 404.1 (M-H)-; HRMS exact mass calcd for(C20H31O5N4+Na) requires m/z 428.2274, found m/z 428.2275.

109

tert-butyl((S)-1-oxo-3-phenyl-1-((6-((S)-pyrrolidine-2-carboxamido)pyridin-2- yl)amino)propan-2-yl)carbamate (124)

The same procedure was followed as for the synthesis of (123);

1 H NMR (500 MHz, CDCl3) δ 1.40 (s, 9H), 1.74-1.78 (m, 3H), 1.99-2.0 (m, 1H), 2.20-2.23(m, 2H), 3.04-3.10 (m, 2H), 3.84-3.87(m, 1H), 4.13(m, 1H), 5.18 (br, 1H), 7.62-7.64(m, 1H), 7.79(m, 1H), 7.89-7.91(m, 1H),7.27- 7.38 (m, 5H), 8.22(m, 13 1H), 9.90(br, 1H); C NMR(125Hz, CDCl3) δ 25.98, 28.40, 28.30, 30.65, 30.96, 47.14, 61.07, 80.08, 109.09, 109.24, 127.7, 128.6, 124.8, 140.10, 149.09, 149.12, 156.32, 170.82, 173.31, 175.09; MS (ESI) 404.1 [M+H]+.

General procedure of the enantioselective aldol reaction: A mixture of CuCl2

(5.4 mg, 0.04mmol, 20mol%), AgSbF6 (27.5mg, 0.08 mmol, 40 mol%), ligand 3 (16.2mg, 0.04 mmol, 20 mol%) in THF (0.6mL), acetone( 0.3mL) was stirred at room temperature for 4 h. Then reaction system was tuned to appropriate temperature and the aldehyde (0.2mmol) was added. The resulting mixture was stirred for 24-48 h. After the reaction was complete (monitored by TLC), the reaction mixture was treated with saturated ammonium chloride solution, and the mixture was extracted with ethyl acetate. After removal of the solvent, (for some of them, mixture 1HNMR was taken to determine the diastereoselectivity) the residue was purified through column chromatography on silica gel (eluent: mixture of Hexane and ethyl acetate) to give the pure products. All aldol products are known 110

compounds and their spectroscopic data are identical with those reported. The ee values were determined by chiral HPLC analysis.

Experimental for 1.8.3

(S)-N-(6-(2-amino-3-methylbutanamido)pyridin-2-yl)benzamide (130a)

General scheme 1.8.3.37

To a stirred solution of N-Boc-L-valine (2.17g, 10 mmol) in CH2Cl2 (100 mL) was added pyridine-2,6-diamine (10 mmol, 1.09g), DCC (2.3g, 10 mmol), HOBt (1.5g, 10 mmol) and DIPEA (1.25 mL, 10mmol) at 0 oC. This reaction mixture was stirred at room temperature for 24 h. The solution was filtered and washed with aqueous NaHCO3. The organic phase was evaporated under reduced pressure and purified by column chromatography (silica gel) to give the pure product A (1.43g).

Product A (0.92g, 3 mmol) was dissolved in THF (30 mL). The solution was cooled down to 0 oC and TEA (1 mL, 6.6 mmol) was added. Then to this solution benzoyl chloride (0.38 mL, 3.3 mmol) was added drop wise at 0 oC. After the solution was stirred at 0 oC for 30 min, the resulting solution was stirred at room temperature overnight. The solid was filtered off and the solvent was removed. The residue was purified through column chromatography (eluent: hexane ethyl acetate, v:v, 3:1) to give the product (1.11g, 90%).

The obtained N-Boc compound (1.11g) was dissolved into DCM (5 mL) and TFA (5 mL). The resulting mixture was stirred at rt for 4h. The reaction mixture was evaporated and the residue dissolved in ethyl acetate. 1 N NaOH solution was used the ethyl acetate solution to tune the pH to 9. The mixture was then extracted with

111

ethyl acetate. The combined organic phase was evaporated to dryness to give the pure product 130a (0.82g, 97%).

25 1 [α]D = +6.5 (c= 0.15, CHCl3); H NMR (500 MHz, DMSO) δ 0.87 (d, J = 7.0 Hz, 3H), 0.98 (d, J = 7.0 Hz, 3H), 2.15-2.17 (m, 1H), 3.42 (m, 1H), 7.51-7.61(m, 3H), 7.87-7.89 (m, 3H), 8.00-8.02 (m, 2H), 10.56 (s, 1H). 13C NMR (125Hz, DMSO) δ 16.24, 19.11, 30.67, 60.16, 109.51, 109.86, 127.07, 128.49, 132.01, 133.87, 140.40, 149.05, 149.77, 165.68, 172.02. MS (ESI) 313.2 (M+H)+; HRMS exact mass calcd for (C17H20N4O2+H) requires m/z 313.1664, found m/z 313.1653.

25 (S)-N-(6-acetamidopyridin-2-yl)-2-amino-3-methylbutanamide(130b) [α]D = 1 +37.0 (c= 0.12, CHCl3); H NMR (500 MHz, DMSO) δ 0.78 (d, J = 7.0 Hz, 3H), 0.92 (d, J = 7.0 Hz, 3H), 2.05-2.10 (m, 4H), 3.22 (m, 1H), 7.73-7.75(m, 3H), 10.29 (s, 1H). 13C NMR (125Hz, DMSO) δ 16.94, 19.90, 24.36, 31.39, 60.49, 108.20, 109.17, 140.77, 149.89, 151.12, 169.69, 174.42. MS (ESI) 248.9 (M-H)- ; HRMS exact mass calcd for (C12H18N4O2+H) requires m/z 251.1508, found m/z 251.1500.

112

25 (S)-2-amino-3-methyl-N-(6-pivalamidopyridin-2-yl)butanamide (130c) [α]D = 1 +3.9 (c= 0.21, CHCl3); H NMR (500 MHz, CD3OD) δ 1.04 (d, J = 6.5 Hz, 3H), 1.09 (d, J = 6.5 Hz, 3H), 1.29 (s, 9H), 3.34 (m, 1H), 7.68 (m, 1H), 7.73 (d, J = 8.0 13 Hz, 1H), 7.82 (d, J = 8.0 Hz, 1H). C NMR (125Hz, CD3OD) δ 15.89, 17.74, 36.15, 36.17，39.43, 56.07, 109.08, 109.23, 139.96, 149.44, 150.53, 169.23,

+ 178.31. MS (ESI) 293.2 (M+H) ; HRMS exact mass calcd for (C15H24N4O2+H) requires m/z 293.1977 found m/z 293.1976.

tert-butyl((S)-1-((6-((S)-2-amino-3-methylbutanamido)pyridin-2-yl)amino)-1- oxo-3-phenylpropan-2-yl)carbamate (131)

To a stirring solution of N-Cbz-L-valine (2.51g, 10 mmol) in CH2Cl2 (100 mL) was added pyridine-2,6-diamine (1.09 g, 10 mmol), DCC (2.3g, 10 mmol), HOBt (1.5g, 10 mmol) and DIPEA (1.25 mL, 10 mmol) at 0oC. This reaction mixture was stirred at room temperature for 24 hours. The solution was filtered and washed with aqueous NaHCO3. The organic phase was evaporated under reduced pressure and purified by column chromatography (silica gel) to give the pure product A (1.7 g, 49%).

N-Boc-L-Phenylalanine (1.0g, 2.9mmol) was dissolved in THF (20 mL). The solution was cooled down to 0 oC. TEA (0.6 mL, 4.4 mmol) was added. Then to this solution ethylchloroformate (0.45 mL, 4.4 mmol) was added drop wise for 15 113

min. After the solution was stirred at 0 oC for 45 min, amine A (1.0 g, 2.9 mmol) was added slowly in 10 mL THF solution at 0 oC for 10 minutes. The resulting solution was stirred at room temperature for 16 h, and then refluxed for 3 h. After cooling down to room temperature, the solid was filtered off and the solvent was removed. The oily product was then dissolved in DCM. The mixture was washed with aqueous NaHCO3 and dried with anhydrous Na2SO4. After removal of the solvent, the residue was purified through column chromatography on silica gel (eluent: Hexane: Ethyl Acetate, v:v, 2:1) to give the product (0.96 g, yield: 56%).1

The obtained compound (0.96 g), 10% Pd/C (200 mg) and methanol (30 mL) were mixed in a 100 mL flask. After stirring under hydrogen (1 atm) for 4 h, the solution was filtered on Celite to remove the Pd/C, and then evaporated to dryness to give the products 131 (0.74 g, yield: 99 % ).

25 1 [α]D = -6.2 (c= 0.08, CHCl3); H NMR (500 MHz, CDCl3) δ 1.15 (d, J = 6.5 Hz, 3H), 1.28 (d, J = 6.5 Hz, 3H), 1.45 (s, 9H), 2.33 (m, 1H), 3.05-3.20 (m, 2H), 3.57- 3.69 (m, 1H), 4.52 (m, 1H), 5.11 (m, 1H), 7.24-7.33 (m, 6H), 7.63-7.73 (m, 2H), 13 7.93 (m, 1H). C NMR (125Hz, CDCl3) δ 16.91, 19.45, 26.87, 27.88, 28.25, 28.84, 63.10, 78.70, 109.25, 110.01, 127.00, 128.55, 128.68, 129.20, 129.31, 129.72, 148.28, 149.05x, 170.24, 174.74. MS(ESI) 456.3 (M+H)+; HRMS exact mass calcd for (C24H33N5O4+H) requires m/z 456.2611, found m/z 456.2604.

114

(2S,2'S)-N,N'-(pyridine-2,6-diyl)bis(2-amino-3-phenylpropanamide) (134)

To a stirring solution of N-Boc-L-phenylalanine (5.3 g, 20 mmol) in CH2Cl2 (50 mL) was added pyridine-2,6-diamine (5 mmol, 500mg), DCC (4.2 g, 20 mmol) and DIPEA (3.7 mL, 20 mmol). This reaction mixture was stirred at room temperature for 48 hrs. The solution was filtered and washed with aqueous NaHCO3. The organic phase was evaporated under reduced pressure and purified by column chromatography (silica gel) to give mono coupled product 132 (35%) and a decoupled product 133 (50%).

The obtained N-Boc protected compound 134 (3.7 g) was dissolved into DCM (5 mL) and TFA (5 mL) and stirred at rt for 4h. The reaction mixture was evaporated and dissolved in Ethyl Acetate. 1 N NaOH solution was used to tune the pH of the solution to 9 and the mixture was extracted with ethyl acetate. The combined organic phases was evaporated to dryness to afford the pure product 134

25 1 (2.0g, 80%). [α]D = -13.3 (c= 0.15, CHCl3); H NMR (500 MHz, CD3OD) δ 2.89 (dd, J = 7.5, 13.5 Hz, 1H), 3.14 (dd, , J = 5.5, 13.5 Hz, 1H), 3.74 (t, J = 6.5Hz, 13 1H), 7.22-7.31 (m, 10H), 7.75-7.85 (m, 3H). C NMR (125Hz, CD3OD) δ 45.03, 61.73, 112.82, 124.01, 132.78, 134.01, 135.14, 143.62, 155.09, 179.18. MS (ESI) + 404.3 (M+H) ; HRMS exact mass calcd for (C23H25N5O2+H) requires m/z 404.2086, found m/z 404.2079.

115

25 (S)-N-(6-acetamidopyridin-2-yl)-2-amino-3-phenylpropanamide (135) [α]D = - 1 8.8 (c= 0.12, CHCl3); H NMR (500 MHz, DMSO) δ 2.06 (s, 3H), 2.71 (dd, J = 9.0, 13.5 Hz, 1H), 3.10 (dd, , J = 4.5, 9.0 Hz, 1H), 3.64 (m, 1H), 7.25-7.27 (m, 5H), 7.75-7.77 (m, 3H), 10.29 (s, 1H). 13C NMR (125Hz, DMSO) δ 24.36, 40.51, 56.86, 108.20, 109.26, 126.75, 128.69, 129.76, 138.84, 140.79, 149.90, 151.12, 169.71, 174.12. MS (ESI) 321.2 (M+Na)+ ; HRMS exact mass calcd for

(C16H18N4O2+H) requires m/z 299.1508, found m/z 299.1500.

General procedure of the enantioselective aldol reaction: A mixture of CuCl2

(5.4 mg, 0.04 mmol, 20 mol%), AgSbF6 ( 27.5 mg, 0.08 mmol, 40 mol%), ligand 130c ( 11.7 mg, 0.04 mmol, 20 mol%), and cyclohexanone (1 mL) was stirred at room temperature for 4 hours. Then the aldehyde (0.2 mmol) was added. The resulting mixture was stirred for 12-48 h. After the reaction was completed (monitored by TLC), the reaction mixture was treated with saturated ammonium chloride solution, and extracted with ethyl acetate. After removal of the solvent, mixture 1H NMR was taken to determine diastereoselectivity. The mixture was purified through column chromatography on silica gel (eluent: mixture of Hexane and ethyl acetate) to give the pure products. All aldol products are known compounds and their spectroscopic data are identical with those reported. The ee values were determined by chiral HPLC analysis.

116

Experimental 1.8.4 (S)-2-amino-3-methyl-N-(pyridin-2-yl)butanamide (139a) General procedure scheme 1.8.4.40

To a stirred solution of N-Boc-L-valine (2.17 g, 10 mmol) in CH2Cl2 (100 mL), 2- amino-pyridine (10 mmol, 0.94 g), BOP (10 mmol, 4.42 g) and DIPEA (1.25 mL, 10 mmol) at 0 oC were added. This reaction mixture was stirred at room temperature for 24 hours. The solution was washed with aqueous NaHCO3. The organic phase was evaporated under reduced pressure and purified by column chromatography (silica gel, eluent hexane/ethyl acetate, v/v, 5/1) to give the pure product A.

The obtained N-Boc compound A (2.2 g) was dissolved into DCM (10 mL) and TFA (10 mL) and stirred at rt for 2 hrs. The reaction mixture was evaporated and dissolved in Ethyl Acetate. 1 N NaOH solution was used to tune the pH of the solution to 8 and the mixture was extracted with ethyl acetate. The solvent was evaporated to give the pure product 139a (1.20 g, 87%). Similar procedure was followed for other ligands.

General procedure of the enantioselective aldol reaction: A mixture of CuCl2

(5.4 mg, 0.04 mmol, 20 mol%) AgSbF6 ( 27.5 mg, 0.08 mmol, 40 mol%), and 0.04 mmol, 20 mol% of the appropriate ligand was stirred at room temperature for 4 hrs. in 1mL cyclohexanone (neat). The appropriate aldehyde (0.2 mmol) was then added. The resulting mixture was stirred for 3-48 hrs. After the reaction was completed (monitored by TLC), the reaction mixture was treated with saturated ammonium chloride solution, and the mixture extracted with ethyl acetate. After removal of solvent, mixture 1HNMR was taken to determine diastereoselectivity. The residue was purified through column chromatography on silica gel (eluent: 117

mixture of Hexane and ethyl acetate,) to give pure products. All aldol products are known compounds and their spectroscopic data are identical with those reported. The ee values were determined by chiral HPLC analysis.

25 (S)-2- amino-3-methyl-N- (pyridin-2-yl) butanamide (139a): [α]D = -21.5(c= 1 0.20, CHCl3); H NMR (300 MHz, CDCl3) δ 0.86 (d, J = 6.9 Hz, 3H), 1.03 (d, J = 7.2 Hz, 3H), 1.53 (br, 2H), 2.37-2.42(m, 2H), 3.38 (d, J = 2.7Hz, 1H), 6.98- 7.03(m, 3H), 7.64-7.71 (m, 1H), 8.24-8.28 (m, 2H), 9.94 (br, 1H). 13C NMR

(75Hz, CDCl3) δ 16. 4, 19.6, 31.3, 61.1, 113.8, 119.5, 138.0, 148.0, 151.5, 173.2. + MS (ESI) 194.0 (M+H) ; HRMS exact mass calcd for (C10H15N3O+Na) requires m/z 216.1113, found m/z 216.1119.

25 (S)-2-amino-N- (pyridin-2-yl) propanamide (139b): [α]D = +5.9 (c= 0.34, 1 CHCl3); H NMR (300 MHz, CDCl3) δ 1.42 (d, J = 6.9 Hz, 3H), 1.65(br, 2H), 3.63 (dd, J = 6.9, 13.8 Hz, 1H), 6.99-7.04 (m, 1H), 7.65-7.71 (m, 1H), 8.20-8.32 13 (m, 2H), 9.85 (br, 1H). C NMR (75Hz, CDCl3) δ 21.5, 51.4, 113.7,119.5, 138, 146.0, 151.5, 174.3. MS (ESI) 188.0 (M+Na); HRMS exact mass calcd for

(C8H11N3O+Na) requires m/z 188.0800, found m/z 188.0805.

118

25 (S)-2-amino-3-pheyl-N- (pyridin-2-yl) propanamide (139c): [α]D = -117.1 (c= 1 0.17, CHCl3); H NMR (300 MHz, CDCl3) δ 1.62 (br, 2H), 2.78 (dd, J = 3.6, 13.8Hz, 2H), 3.38 (dd, J = 3.9, 13.8Hz, 2H), 3.42 (d, J = 4.8Hz, 1H), 7.02-7.06 (m, 1H), 7.24-7.36 (m, 5H), 7.69-7.75 (m, 1H), 8.28-8.31(m, 1H), 10.00 (br, 1H). 13C

NMR (75Hz, CDCl3) δ 40.4, 56.6, 113.2, 119.0, 126.3, 128.2, 128.7, 137.2, 137.4, 147.4, 172.4. MS (ESI) 242.1 (M+H)+; HRMS exact mass calcd for

(C14H15N3O+Na) requires m/z 264.1113, found m/z 264.1104.

25 (2S,3S)-2-amino-3-methyl-N- (pyridin-2-yl) pentanamide (139d): [α]D = - 1 4.07(c= 8.2, CHCl3); H NMR (500 MHz, CDCl3) δ 0.90 (m, 3H), 1.02 (d, J = 7.0 Hz, 3H), 1.39-1.44 (m, 1H), 1.57 (br 1H), 2.11-2.13 (m, 1H), 3.43(d, J = 3Hz, 1H), 7.00-7.02 (m, 1H), 7.68-7.70 (m, 1H), 8.25-8.29 (m, 2H), 10.01 (br, 1H). 13C NMR

(125Hz, CDCl3) δ 11.9, 16.3, 23.8, 38.0, 60.3, 113.7, 119.6, 138.2, 147.9, 151.2, + 173.5. MS (ESI) 208.1 (M+H) ; HRMS exact mass calcd for (C11H17N3O+Na) requires m/z 230.1269, found m/z 230.1261.

119

25 (2S,RS)-2-amino-3-(benzyloxy)-N- (pyridin-2-yl) butanamide (139e): [α]D = - 1 8.13 (c= 3.42, CHCl3); H NMR (500 MHz, CDCl3) δ 1.32 (d, J = 6.5 Hz, 3H),1.89 (br, 2H), 3.38 (m, 1H), 4.36 (m, 1H), 4.49 (d, J = 11.5 Hz, 1H), 4.60 (d, J = 11.5Hz, 1H), 7.04-7.06 (m, 1H), 7.28 (s, 5H), 7.72 (m, 1H), 8.28-8.34 (m, 2H) 13 10.22 (br, 1H). C NMR (125Hz, CDCl3) δ 17.2, 59.9, 71.5, 74.8, 113.7, 119.7, 127.7, 128.3, 138.2, 138.3, 148.1, 151.3, 172.6. MS (ESI) 286.1 (M+H)+; HRMS exact mass calcd for (C16H19N3O2+Na) requires m/z 308.1375, found m/z 308.13.1352.

25 (S)-2-amino-3-(1-H-indol-2-yl)-N-(pyridin-2-yl) propanamide (139f): [α]D = - 1 9.40 (c= 3.52, CHCl3); H NMR (500 MHz, CDCl3) δ 1.62 (br, 2H), 2.92-2.97 (m, 1H), 3.44 (d, J = 12 Hz, 1H), 3.79 (d, J = 6 Hz, 1H), 6.97-7.16, (m, 4H), 7.31 (d, J = 8 Hz, 1H), 7.610-7.68 (m, 2H), 8.27 - 8.34 (m, 2H), 9.04 (s, 1H), 10.07 (br, 1H). 13 C NMR (125Hz, CDCl3) δ 30.6, 56.1, 111.0, 111.5, 113.9, 118.8, 119.6, 119.9, 122.2, 123.5, 127.4, 136.6, 138.5, 148.0, 151.2, 174.2. MS (ESI) 281.1 (M+H)+

25 (S)-2- amino-3,3-dimethyl-N- (pyridin-2-yl) butanamide (139g): [α]D = -20.0 1 (c= 0.1, CHCl3); H NMR (300 MHz, CDCl3) δ 1.03 (s, 9H), 1.67 (br, 2H), 3.25 (s, 1H), 6.98-7.00 (m, 1H), 7.64-7.68 (m, 1H), 8.21-8.26 (m, 2H), 9.45 (br, 1H). 120

13 C NMR (75Hz, CDCl3) δ 26.8, 34.6, 65.0, 113.8, 119.6, 138.2, 147.9, 151.1, 172.6. MS (ESI) 208.1 (M+H)+

25 (S)-N-(pyridine-2-yl)pyrrolidine-2-carboxamide (140): [α]D = -117.1 (c= 0.17, 1 CHCl3); H NMR (500 MHz, CDCl3) δ 1.32 (d, J = 6.5 Hz, 3H),1.89 (br, 2H), 3.38 (m, 1H), 4.36 (m, 1H), 4.49 (d, 11.5 Hz, 1H), 4.60 (d, 11.5Hz, 1H), 7.04-7.06 (m, 1H), 7.28 (s, 5H), 7.72 (m, 1H), 8.28-8.34 (m, 2H) 10.22 (br, 1H). 13C NMR

(125Hz, CDCl3) δ 17.2, 59.9, 71.5, 74.8, 113.7, 119.7, 127.7, 128.3, 138.2, 138.3, 148.1, 151.3, 172.6. MS (ESI) 286.1 (M+H)

121

Experimental 1.8.5

(S)-N-(pyridin-2-yl)pyrrolidine-2-carboxamide (140)

The method described in section 1.8.4 synthetic scheme 1.8.4.40 was used to prepare 140. Yield: 56% ;

1 H NMR (300 MHz, CDCl3) δ1.74-2.28 (m, 5H), 3.02-3.11 (m, 2H), 3.87-3.95 (m, 1H), 6.90-7.05 (m, 1H), 7.60-7.81 (m, 1H), 8.21-8.39 (m, 2H), 10.20 (br, 1H). MS (ESI) 214.1 (M+Na) +.

(S)-N-phenylpyrrolidine-2-carboxamide (148)

N-carbobenzyloxyl-L-Proline (4.48 g, 18 mmol) was dissolved in THF (40 mL). The solution was cooled down to 0oC, and then TEA (2.5 mL, 18 mmol) was added. To this solution ethylchloroformate (1.953 g, 18 mmol) was added drop wise for 15 min. The solution was stirred at 0oC for 45 min, aniline (1.41 g, 15 mmol) was added slowly for 10 minutes in 10 mL THF solution at 0oC. The resulting solution was stirred at room temperature for 16 hrs, and then refluxed for 4 hours. After cooling down to room temperature, the solid was filtered off and the solvent was removed under reduced pressure to give a brown oily solid. The oil was dissolved in DCM. The mixture was washed with aqueous NaHCO3 and dried with anhydrous Na2SO4. After removal of the solvent, the residue was purified

122

through column chromatography on silica gel (eluent: DCM: ethyl acetate, v:v, 10:1) to give A (2.8 g)

The obtained N-Cbz protected compound A (2.8 g), 10% Pd/C (500 mg) and methanol (40 mL) were mixed in a 100 mL two-neck flask. After stirring under hydrogen (1 atom) for 4 hrs, the solution was filtered through Celite to remove the Pd/C, and then evaporated to dryness to give the product ( 1.6 g ).

(S)-N-phenylpyrrolidine-2-carboxamide (148); Yield: 65%; 1H NMR (300 MHz,

CDCl3) δ1.68-1.78 (m, 2H), 1.99-2.20 (m, 3H), 3.46-3.49 (m, 2H), 3.84 (m, 1H), 7.06-7.08 (m, 1H), 7.29-7.32 (m, 2H), 7.56-7.59 (m, 2H), 9.70 (br, 1H).

General procedure for the synthesis of aminals

A mixture of 140 (38 mg, 0.2 mmol), aldehyde (0.2 mmol), Cu(OTf)2 (7.3 mg, 0.02 mmol) was dissolved in dry ethanol (2 mL)and refluxed for 24 hours. When the aldehyde was completely consumed, the reaction system was cooled down to rt and saturated ammonium chloride solution was added. The mixture was extracted with ethyl acetate. After removal of the solvent, mixture 1H NMR was taken to determine the diastereoselectivity. The mixture was purified by column chromatography (eluent: hexane: ethyl acetate, v:v, 3:1).

123

(3R,7aS)-3-(4-nitrophenyl)-2-(pyridin-2-yl)-hexahydropyrrolo[1,2-e]imidazol- 1-one (144a)

1 Yield: 86%; H NMR (500 MHz, CDCl3) δ 1.87-1.89 (m, 2H), 2.19-2.87 (m, 2H), 2.87-2.89 (m, 1H), 3.44-3.46 (m, 1H), 4.00-4.01 (m, 1H), 6.41 (s, 1H), 6.99 (d, J = 0.5 Hz, 1H), 7.47 (m, 2H), 7.71 (m, 1H), 8.13-8.17 (m, 3H), 8.43 (d, J = 8.5 Hz, 13 1H) C NMR (125Hz, CDCl3) δ 24.86, 27.49, 55.97, 65.25, 80.28, 114.04, 120.14, 123.77, 127.13, 138.09, 147.48, 147.67, 147.73, 150.36, 175.26. MS (ESI) 347.1 (M+Na)+.

(3S,7aS)-3-(4-nitrophenyl)-2-(pyridin-2-yl)-hexahydropyrrolo[1,2-e]imidazol- 1-one (145a)

1 H NMR (500 MHz, CDCl3) δ 1.78-1.80 (m, 2H), 2.23-2.32 (m, 3H), 2.41-2.43 (m, 1H), 4.09-4.12 (m, 1H), 6.69 (s, 1H), 6.99 (m, 1H), 7.42-7.44 (m, 2H), 7.74-7.78 13 (m, 1H), 8.05 (m, 2H), 8.15-8.17 (m, 2H) C NMR(125Hz, CDCl3) δ 24.91, 26.78, 49.42, 66.12, 77.51, 116.50, 120.21, 123.47, 128.31, 137.76, 143.61, 147.49, 147.56, 150.50, 176.93. MS (ESI) 347.1 (M+Na)+.

124

(3R,7S)-3-(3-nitrophenyl)-2-(pyridin-2-yl)-hexahydropyrrolo[1,2-e]imidazol- 1-one (144b)

1 Yield: 64% ; H NMR (500 MHz, CDCl3) δ 1.88-1.90 (m, 2H), 2.18-2.22 (m, 2H), 2.88-2.90 (m, 1H), 3.49 (m, 1H), 4.05 (m, 1H), 6.43 (s, 1H), 6.98-7.01 (m, 1H), 7.42-7.45 (m, 1H), 7.61 (m, 1H), 7.69-7.72 (m, 1H), 8.08-8.10 (m, 1H), 8.17 (m, 1 13 H), 8.24 (s, 1 H). 8.41 (m, 1H) C NMR(125Hz, CDCl3) δ 24.89, 27.45, 55.97, 65.30, 80.20, 114.23, 120.25, 121.89, 123.00, 129.47, 132.19, 134.60, 137.42, 138.17, 147.75, 148.43, 189.68. MS (ESI) 347.1 (M+Na)+

(3R,7S)-3-(2-nitrophenyl)-2-(pyridin-2-yl)-hexahydropyrrolo[1,2-e]imidazol- 1-one (144c)

1 Yield: 70% ; H NMR (500 MHz, CDCl3) δ 1.84-1.86 (m, 2H), 2.15-2.19 (m, 2H), 2.86-2.88 (m, 1H), 3.49 (m, 1H), 3.90 (m, 1H), 6.97 (m, 1H), 6.99 (s, 1H), 7.11 (m, 1H), 7.37-7.42 (m, 2H), 7.69-7.72 (m, 1H), 7.90 (m, 1H), 8.17 (m, 1 H), 8.43 (m, 13 1 H). C NMR(125Hz, CDCl3) δ 24.84, 27.39, 55.88, 65.01, 76.73, 113.39, 125

119.96, 125.20, 126.28, 128.60, 132.83, 135.57, 137.98, 147.83, 148.97, 150.46, 175.95. MS (ESI) 347.1 (M+Na)+

4-((3R,7S)-1-oxo-2-(pyridin-2-yl)-hexahydro-1H-pyrrolo[1,2-e]imidazol-3- yl)benzonitrile (144d)

1 Yield: 51% ; H NMR (500 MHz, CDCl3) δ 1.88-1.93 (m, 2H), 2.19-2.24 (m, 2H), 2.87-2.89 (m, 1H), 3.46-3.49 (m, 1H), 4.01-4.03 (m, 1H), 6.39 (s, 1H), 7.00-7.03 (m, 1H), 7.42 (d, J = 8.0 Hz, 2H), 7.59 (d, J = 8.0 Hz, 2H), 7.71-7.74 (m, 1H), 13 8.17 (d, J = 8.5 Hz, 1 H), 8.43 (d, J = 8.5 Hz, 1 H). C NMR(75Hz, CDCl3) δ 24.84, 27.79, 56.10, 65.50, 80.80, 114.40, 118.35, 120.09, 127.28, 129.77, 132.29,132.85, 138.01, 147.76, 150.76, 174.92. MS (ESI) 327.1 (M+Na)+

126

(3R,7S)-3-(4-chlorophenyl)-2-(pyridin-2-yl)-hexahydropyrrolo[1,2-e]imidazol- 1-one (144e)

1 Yield: 45% ;Yield: 86% ; H NMR (500 MHz, CDCl3) δ 1.85-1.88 (m, 2H), 2.15- 2.19 (m, 2H), 2.82-2.84 (m, 1H), 3.42 (t, J = 5.0 Hz, 1H), 4.01 (dd, J = 5.0, 8.5 Hz, 1H), 6.35 (s, 1H), 6.96-6.99 (m, 1H), 7.24 (m, 4H), 7.67-7.71 (m, 1H), 8.20 (m, 13 1H), 8.42 (m, 1 H) C NMR(125Hz, CDCl3) δ 24.82, 27.33, 55.74, 65.23, 80.45, 114.28, 119.97, 127.52, 128.70, 133.65, 137.93, 139.01, 147.75, 150.61, 175.49. MS (ESI) 336.1 (M+Na)+.

(3R,7S)-3-phenyl-2-(pyridin-2-yl)-hexahydropyrrolo[1,2-e]imidazol-1-one (144f)

1 Yield: 30%; H NMR (500 MHz, CDCl3) δ 1.86-1.89 (m, 2H), 2.16-2.19 (m, 2H), 2.84-2.86 (m, 1H), 3.45-3.47 (m, 1H), 4.05-4.07 (m, 1H), 6.41 (s, 1H), 6.95-6.98 (m, 1H), 7.22-7.30 (m, 5H), 7.68-7.69 (m, 1H), 8.19-8.20 (m, 1H), 8.42 (d, J = 8.5 13 Hz, 1H). C NMR(125Hz, CDCl3) δ 24.86, 27.27, 55.82, 65.24, 81.06, 114.44, 119.93, 126.00, 128.01, 128.67, 137.92, 140.26, 147.86, 150.79, 175.77. MS (ESI) 302.1 (M+Na)+.

127

(3R,7S)-2-(pyridin-2-yl)-3-p-tolyl-hexahydropyrrolo[1,2-e]imidazol-1-one (144g)

1 Yield: 17%; H NMR (500 MHz, CDCl3) δ 1.90-1.93 (m, 2H), 2.20-2.23 (m, 2H), 2.32 (s, 3H), 2.87-2.89 (m, 1H), 3.48-3.50 (m, 1H), 4.09-4.12 (m, 1H), 6.43 (s, 1H), 7.00-7.02 (m, 1H), 7.13-7.14 (m, 2H), 7.22-7.24 (m, 2H), 7.71-7.75 (m, 1H), 13 8.25-8.26 (m, 1H), 8.46 (d, J = 8 Hz, 1H). C NMR(125Hz, CDCl3) δ 21.09, 24.83, 27.25, 55.71, 65.24, 80.98, 114.47, 119.83, 125.88, 129.30, 137.40, 137.67, 137.83, 147.85, 150.87, 175.77. MS (ESI) 316.1 (M+Na)+.

(3R,7S)-3-(4-nitrophenyl)-2-phenyl-hexahydropyrrolo[1,2-e]imidazol-1-one (146a)

1 Yield: 65%； H NMR (500 MHz, CDCl3) δ 1.87-1.92 (m, 2H), 2.18-2.22 (m, 2H), 2.88-2.93 (m, 1H), 3.41-3.45 (m, 1H), 3.96-3.99 (m, 1H), 5.75 (s, 1H), 7.10- 7.13 (m, 1H), 7.24-7.30 (m, 2H), 7.40 (d, J = 8 Hz, 2H), 7.46 (d, J = 8.5Hz, 2H), 13 8.16 (d, J = 8.5 Hz, 2H). C NMR (125Hz, CDCl3) δ 24.84, 27.63, 56.21, 64.39,

128

82.59, 121.19, 124.17, 125.60, 127.07, 129.22, 137.01, 146.49, 147.90, 174. 39. MS (ESI) 346.1 (M+Na)+.

(3R,7S)-3-(3-nitrophenyl)-2-phenyl-hexahydropyrrolo[1,2-e]imidazol-1-one (146b)

1 Yield: 68% ; H NMR (500 MHz, CDCl3) δ 1.88-1.92 (m, 2H), 2.18-2.23 (m, 2H), 2.90-2.95 (m, 1H), 3.42-3.46 (m, 1H), 4.00-4.03 (m, 1H), 5.78 (s, 1H), 7.10-7.13 (d, J = 7.5 Hz, 1H), 7.24-7.30 (m, 2H), 7.40-7.49 (m, 3H), 7.57 (m, 2H), 8.11 (m, 13 1H), 8.21 (s, 1H) C NMR(125Hz, CDCl3) δ 24.89, 27.75, 56.20, 64.43, 82.65, 121.56, 121.91, 123.63, 125.78, 129.32, 130.02, 132.06, 136.92, 141.74, 148.65, 174.24. MS (ESI) 346.1 (M+Na)+

129

(3R,7S)-3-(2-nitrophenyl)-2-phenyl-hexahydropyrrolo[1,2-e]imidazol-1-one (146c)

1 Yield: 65% ; H NMR (500 MHz, CDCl3) δ 1.82-1.85 (m, 2H), 2.12-2.19 (m, 2H), 2.83-2.85 (m, 1H), 3.45 (m, 1H), 3.75 (m, 1H), 6.64 (s, 1H), 7.12 (d, J = 7.5 Hz, 1H), 7.23-7.33 (m, 3H), 7.45-7.48 (m, 2H), 7.56-7.59 (m, 2H), 8.02 (d, J = 7.5 Hz, 13 1H), C NMR(75Hz, CDCl3) δ 24.87, 27.54, 56.38, 64.23, 78.49, 120.06, 125.15, 125.59, 126.89, 129.28, 133.14, 134.46, 138.07, 149.31, 175.17. MS (ESI) 346.1 (M+Na)+

(3R,7S)-3-(4-chlorophenyl)-2-phenyl-hexahydropyrrolo[1,2-e]imidazol-1-one (146d)

1 Yield: 34% ; H NMR (500 MHz, CDCl3) δ 1.86-1.91 (m, 2H), 2.17-2.20 (m, 2H), 2.83-2.89 (m, 1H), 3.38-3.42 (m, 1H), 3.98-4.01 (m, 1H), 5.63 (s, 1H), 7.09-7.12 (d, 1H), 7.21-7.26 (m, 2H), 7.28-7.30 (m, 3H), 7.40-7.43 (m, 2H). 13C NMR

(125Hz, CDCl3) δ 24.69, 27.76, 55.99, 64.55, 83.40, 121.62, 125.22, 127.72, 128.85, 128.93, 134.41, 137.72, 138.52, 174.30. MS (ESI) 335.1 (M+Na)+.

130

(3R,7S)-2,3-diphenyl-hexahydropyrrolo[1,2-e]imidazol-1-one (146e)

1 Yield: 41% ; H NMR (500 MHz, CDCl3) δ 1.87-1.91 (m, 2H), 2.18-2.22 (m, 2H), 2.86-2.88 (m, 1H), 3.42-3.44 (m, 1H), 4.01-4.04 (m, 1H), 5.66(s, 1H), 7.07-7.10 (m, 1H), 7.25-7.28 (m, 2H), 7.28-7.30 (m, 3H), 7.32-7.35 (m, 2H), 7.45-7.47 (m, 13 2H). C NMR (125Hz, CDCl3) δ 24.82, 27.50, 56.08, 64.37, 83.63, 121.12, 125.10, 126.09, 128.60, 129.00, 129.09, 137.69, 139.37, 174.91. MS (ESI) 279.1 (M+H)+.

131

Experimental for 1.8.6

1'-hydroxy-[1,1'-bi(cyclohexan)]-2-one (150). To 1mL of cyclohexanone, were added appropriate amounts of metal and the catalyst. This mixture was allowed to stir at rt for 1-7days. The resulting mixture was diluted with aqueous ammonium chloride solution then extracted with ethyl acetate. The solvent was removed in vacou, to afford an oily compound that was purified using column chromatography hexanes/ ethyl acetate. v/v, 2:1.

1 H NMR (500 MHz, CDCl3) δ 1.53- 1.63 (m, 2H), 1.66- 1.72 (m, 3H), 1.90- 1.92 (m, 7H), 2.05-2.08 (m, 1H), 2.16-2.20 (m, 2H), 2.29- 2.41 (m, 3H), 3.64 (br, 1H). 13 C NMR (125MHz, CDCl3) δ 22.5, 25.4, 26.7,26.9, 30.10, 41.7, 58.5, 69.8, 214.9 MS (ESI) 219.1 (M+Na);

2-(1-hydroxycyclohexyl)-1-phenylethanone (152). 0.5 mL of cyclohexanone was mixed with 5% of the catalyst. The resulting mixture was stirred at room temperature for 5 hrs, at which time 0.5 mL of acetophenone was added. The mixture was allowed to stir at rt for 3-7days. The resulting mixture was quenched by addition of aqueous ammonium chloride solution and was then extracted with ethyl acetate. The solvent was removed in vacou to afford an oily compound that was purified by column chromatography hexanes/ ethyl acetate, v/v,2/1).

132

1 H NMR (500 MHz, CDCl3) δ 1.40- 1.44 (m, 4H), 1.65- 1.72 (m, 4H), 3.07 (s 2H), 3.95 (br, 1H), 7.41-7.44 (m, 2H), 7.52-7.55 (m, 1H), 7.90- 7.92 (m, 2H). 13C NMR

(125MHz, CDCl3) δ 21.97, 25.78, 37.80, 47.73, 70.97, 128.11, 128.66, 133.52. 137.52, 201.92 MS (ESI) 219.0 (M+H)+.

1-(1-Hydroxycyclohexyl)propan-2-one (153). 0.2 mL of cyclohexanone was mixed with 0.2 mL acetone and 5% of the catalyst. The reaction mixture was allowed to stir at rt for 3 days. The resulting mixture was diluted with aqueous ammonium chloride solution, and was then extracted with ethyl acetate. The solvent was removed in vacou to afford an oily compound that was purified using column chromatography hexanes/ ethyl acetate v/v, 3/1).

1 H NMR (500 MHz, CDCl3) δ 1.32- 1.38 (m, 4H), 1.57- 1.66 (m, 4H), 2.12 (s, 13 3H), 3.56 (s, 2H), 3.92 (br, 1H). C NMR (125MHz, CDCl3) δ 21.89, 25.66, 32.02, 37.50, 52.89, 70.59, 210.97. MS (ESI) 188.0 (M+Na).

133

(S)-2-Amino-N,3-dimethyl-N-(pyridin-2-yl)butanamide (160)

To a stirring solution of N-Boc-L-valine (2.17 g, 10 mmol) in CH2Cl2 (100 mL), N-methylpyridin-2-amine (10 mmol, 1.08 g), and DCC (10 mmol, 2.06 g) were added at rt. This reaction mixture was stirred at room temperature for 36 hrs. The solution was washed with aqueous NaHCO3. The organic phase was evaporated under reduced pressure and purified by column chromatography (eluent hexane/ethyl acetate, v/v, 3/1) to give the pure product.

The obtained N-Boc protected compound A (2.2 g) was dissolved in DCM (10 mL) and TFA (10 mL), and the solution was stirred at rt for 2 hrs. The reaction mixture was evaporated and dissolved in ethyl acetate. 1 N NaOH solution was used to tune the pH of the solution to 8. The mixture was extracted with ethyl acetate. The combined organic phase was evaporated to dryness to afford the pure product 160 (1.20 g, 87%). Similar procedure was followed for ligands.

1 H NMR (500 MHz, CDCl3) δ 0.92- 0.96 (m, 6H), 2.26- 2.29 (d, 1H), 2.72 (s, 3H), 3.97-3.99(m, 1H), 5.07 (m, 1H), 6.35-6.36 (m, 1H), 6.57-6.66 (m, 2H), 7.35-7.38 13 (m, 1H), 8.02 (s, 1H). C NMR (125Hz, CDCl3) δ 11. 9, 19.6, 25.9, 30.69, 62.1, 107.7, 113.9, 137.7, 147.9, 158.4, 173.4. MS (ESI) 194.0 (M+H)+; HRMS exact mass calcd for (C10H15N3O+Na) requires m/z 216.1113, found m/z 216.1119.

N-(pyridin-2-ylmethyl)pyrrolidine-2-carboxamide (161). 1H NMR (500 MHz,

CDCl3) δ 1.65- 1.70 (m, 2H), 1.90- 1.92 (m, 1H), 2.09- 2.12 (m, 1H),2.66 (br, 1H) 134

2.89- 2.99(m, 2H), 3.77- 3.80 (m, 1H), 4.48-4.52 (m, 2H), 7.10-7.19 (m, 2H), 7.56- 13 7.60 (m, 1H), 8.48- 8.49 (m, 2H). C NMR (125Hz, CDCl3) δ 22. 3, 25.3, 25.9, 27.3, 45.8, 48.6, 63.2, 79.1, 122.2,122.3, 136.7, 148.9, 158.2, 176.0. MS (ESI) 194.0.

(S)-2-amino-3-methyl-N-(pyridin-2-ylmethyl)butanamide (162)

1 H NMR (300 MHz, CDCl3) δ 0.75- 0.92 (m, 6H), 2.20- 2.26 (d, 1H), 3.21- 3.22 (m, 1H), 4.48-4.50(m, 2H), 7.08- 7.20 (m, 2H), 7.54- 7.60 (m, 1H), 8.11 (s, 1H), 13 8.45- .47 (m, 1H). C NMR (125Hz, CDCl3) δ 16. 2, 19.7, 31.0, 44.3, 60.4, 121.9, 122.2, 136.7, 149.1, 157.1, 174.7. MS (ESI) 194.0.

135

General procedure for the reaction between isatin and (E)-4-phenylbut-3-en- 2-one 6'-phenyl-5',6'-dihydrospiro[indoline-3,2'-pyran]-2,4'(3'H)-dione

A mixture of the metal of (0.04 mmol, 20 mol%) and of the appropriate ligand (0.08 mmol, 40 mol%) was stirred at room temperature for 4 hrs. Then 30.1mg (0.2 mmol) of isatin and 58.8mg (0.4mmol) of (E)-4-phenylbut-3-en-2-one were added. The reaction mixture was monitored by TLC. After the reaction was completed, the reaction mixture was treated the with saturated ammonium chloride solution, and extracted with ethyl acetate. After removal of the solvent mixture, 1HNMR was taken to determine the regioselectivity. The residue was purified through column chromatography (eluent: mixture of hexane /ethyl acetate v/v, 3/1,) to give the pure products.

1 H NMR (500 MHz, CDCl3) δ 2.60 (d, J = 15Hz, 1H), 2.72 (d, J = 11Hz, 1H), 2.83 -2.86 (m, 1H), 2.93 (d J = 15Hz, 2H), 5.92-5.95 (m, 1H), 6.87-6.87 (m, 1H), 13 7.09-7.10 (m, 1H), 7.24 -7.44 (m, 7H), 8.06 (s, 1H) C NMR (125MHz, CDCl3) δ 45.62, 48.84, 73.58, 78.36, 110.56, 123.48, 124.41, 126.05, 128.26, 128.68, 129.00, 130.58, 140.36, 140.58, 176.43, 203.61. MS (ESI) 188.0 (M+Na).

136

Reference

1. Moriuch, T.; Hirao, T.,Design of Ferrocene-dipeptide Bioorganometallic Conjugates to Induce Chirality Organized Structures. Acc. Chem. Res. 2010, 43, 1040. 2. Collins, A. N; Sheldrake, G. N.; Crosby, J. Charility in Industry II: Developments in the Manufacture and Applications of Optical active Compounds. J. Wiley and Sons: New York. 1998. 389 pp. ISBN 0-471-98284-9. 3. Gellman, A. T. Chiral Surfaces: Accomplishments and Challenges. ACS Nano. 2010, 4, 5. 4. Farina, V.; Reeves, J. J.; Senanayake, C. H.; Song, J. J.Asymmetric Synthesis of Active Pharmaceutical Ingrediants. Chem. Rev. 2006, 106, 2734. 5. Almeida, D. R. R.; Gasparro, D. M.; Pisterzi, L. F.; Varro, A.; Penke, B.; Papp, J. Gy.; Csizmadia, I. G. Molecular Study on the Enantiomeric Relationships of Carvedilol Fragment A, 4-(2-Hydroxypropoxy) carbazol, along with Selected Analogues. J. Phys. Chem. A. 2003, 107, 5594. 6. Noyori, R.; Asymmetric Catalysis Organic Synthesis; Wiley: New York, 1994 7. Jacobsen, E. N.; Pfaltz, A.; Yamamoto, H.; Comprehensive Asymmetric Catalysis; Springer; Berlin, 1999 Vol1-3. 8. Ojima, I.; Ed. Catalytic Asymmetric Synthesis, 2nd ed.; Wiley–VCH, New York 2000. 9. Eriksson, T.; Bjorkman, S.; Hoglund, P. Clinical Pharmacology of Thalidomide. Eur. Clin. Pharmacol. 2001,57, 365. 10. Pasteur, L. Optical Activity. Ann. Chem. 1948, 442. 11. Jean, J.; Collet, A.; Wilen, S. H. Enantiomers, Racemates and Resolution; Kriege Publishing Company, Florida, 1991. 12. Fujima, Y.; Ikunaka, M.; Inoue, T.; Matsumoto, J. Synthesis of (S)-3-(N- Methylamino)-1-(2-thienyl)propan-1-ol: Revisiting Eli Lilly's Resolution−Racemization−Recycle Synthesis of Duloxetine for Its Robust Processes. Org. Process Res. Dev. 2006, 10, 905.

137

13. Skupinska, K.A.; McEachern, E. J.; Baird, I. R.; Skerlj, R.T.; Bridger, G.T. Enzymatic Resolution of Bicyclic 1-Heteroarylamines Using Candida antarctica Lipase B J. Org. Chem. 2003, 68, 3546. 14. Cox, G. Preparative Enantioselective Chromatography; Wiley-Blackwell, 2005. 15. Mason, S. F.; Tranter, G.E. Proc. R. London A, 1985, 397, 45. 16. Sybilska, D.; Bielejewska, A.; Nowakowski, R.; Duszczyk, K.; Jurczak, J. Improved chiral recognition of some compounds via the simultaneous use of /?- cyclodextrin and its permethylated derivative in a reversed-phase high- performance liquid chromatographic system J. Chromatogr. 1991, 625, 349. 17. Klar, U.; Bobo, R.; Kuczynski, F.; Schwed, W.; Berger, M.; Skuballa, W.; Buchmann, B. Efficient Chiral Pool Synthesis of the C1–C6 Fragment of Epothilones Synthesis 2005, 301. 18. Zhu, B.; Panek, J. S. Total Synthesis of Epothilone A. Org. Lett. 2000, 2, 2575. 19. Corey, J. E.; Cheng, X-M. The logical of Chemical Synthesis. Wiley- Interscience, 1995. 20. Walsh, P. J.; Kozlowski, C. M. Fundamentals of asymmetric Catalysis. Maple Vail Manufacturing Group, 2009. 21. Lee, A.; Michrowska, A.; Sulzer-Mosse, S.; List, B. The Catalytic Asymmetric Knoevenagel Condensation Angwe. Chem., Int. Ed. 2011, 50, 1707. 22. Bartok, M. Unexpected Inversions in Asymmetric Reactions: Reactions with Chiral Metal Complexes, Chiral Organocatalysts, and Heterogeneous Chiral Catalysts. Chem. Rev. 2010, 110, 1663. 23. Press Release: The 2001 Noble Prize in Chemistry” Nobleprize.org. 24. Faber, K.: Biotransformations in Orgnic Chemistry, 4th ed., Springer-Verlag, Berlin 2000. 25. List B, Asymmetric Organocatalysis, Springer, Berlin 2010. 26. Dhake, K.P.; Tambade, P.J.; Qureshi, Z. S.; Shinghal, R. R.; Bhanage, B. M. HPMC-PVA Film Immobilized Rhizopus oryzae Lipase as a Biocatalyst for Transesterification Reaction. ACS, Catal. 2011, 1, 316. 27. Santacoloma, P.A.; Sin, G.; Gernaey, K. V.; Woodley, J. Multienzyme- Catalyzed Processes: Next-Generation Biocatalysis. M. Org. Proc. Res. Dev. 2011, 15, 203. 138

28. Walton, A. Z.; Conerly, C. W.; Pompeu, Y.; Sullivan, B.; Stewart, J. D. Biocatalytic Reductions of Baylis–Hillman Adducts. ACS Cat. 2011, 1, 989. 29. Astruc, D. Organometallic Chemistry and Catalysis. Springer-Verlag Berlin Heidelberg, 2007. 30. Knowles, W. S. Asymmetric hydrogenation. Acc.Chem. Res. 1983, 16, 106. 31. Luo, M.; Yan, B. Enantioselective henry reactions catalyzed by chiral N-metal complexes containing R(+)/S(-)-a-ethylphenyl amines. Tetrahedron lett. 2010 51 5577. 32. Sharpless, B. K.; Woodard, S. S.; Fin, M. G. On the mechanism of titanium- tartrate catalyzed asymmetric epoxidation. Pure Appl. Chem. 1983, 55, 1823. 33. Yoon, T. P.; Jacobsen, E. N. Privilaged Chiral catalysts. Science 2003, 299, 1691. 34. Jørgensen, K. A.; Johannsen, M.; Yao, S.; Audrain, H.; Thorhauge, J. Catalytic Asymmetric Addition Reactions of Carbonyls. A Common Catalytic Approach. Acc. Chem. Res. 1999, 32, 605.

35. Desimoni, G.; Faita, G.; Jørgensen, K. A. C2-Symmetric Chiral Bis(Oxazoline) Ligands in Asymmetric Catalysis. Chem. Rev. 2006, 106, 356. 36 Johnson, J. S.; Evans, D. A. Chiral Bis(oxazoline) Copper(II) Complexes: Versatile Catalysts for Enantioselective Cycloaddition, Aldol, Michael, and Carbonyl Ene Reactions. Acc. Chem. Res. 2000, 33, 325. 37. Gibson, V. C.; Redshaw, C.; Solan, G. A. Bis(imino)pyridines: Surprisingly Reactive Ligands and a Gateway to New Families of Catalysts. Chem. Rev. 2007, 107, 1745. 38. Pfaltz, AChiral semicorrins and related nitrogen heterocycles as ligands in asymmetric catalysis. Acc. Chem. Res. 1993, 26, 339. 39. Barleizao, C.; Garcia, H. Chiral Salen Complexes: An Overview to Recoverable and Reusable Homogeneous and Heterogeneous Catalyst. Chem. Rev. 2006, 106, 3987. 40. Berthod, M.; Mignani, G.; Woodward, G.; Lemaire, M. Modified BINAP: The How and the Why Chem. Rev. 2005, 105, 1801. 41. Hajos, Z. G.; Parrish, D. R Asymmetric Synthesis of Bicyclic Intermediates of Natural Product Chemistry. J. Org. Chem. 1974, 39, 1615.

139

42. Erkkilä, A.; Majander, I.; Piihko, P. M. Iminium Catalysis. Chem. Rev. 2007, 107, 5416. 43. Mukherjee, S.; Yang, J. W.; Hoffmann, S.; List, B. Asymmetric Enamine Catalysis. Chem. Rev. 2007, 107, 5471. 44. List, B. Asymmetric Aminocatalysis, Synlett. 2001, 1675. 45 Jarvo, E. R.; Miller, S. J. Amino Acids and Peptides as Asymmetric Organocatalysts., Tetrahedron 2002, 58, 2481. 46. Hajos, Z. G.; Parrish, D.R., German Patent. 1971, D.E, 2102623. (b) Eder, U.; Sauer, G.R.; Wiechert, R. German Patent. 1971, D.E, 2014757. 47. List, B.; Lerner, R. A.; Barbas, C. F. III. Proline-Catalyzed Direct Asymmetric Aldol Reactions. J. Am. Chem. 2000, 122, 2395. 48. Brown, H. C.; Brewster, J. H.; Shechter, H. An Interpretation of the Chemical Behavior of Five- and Six-membered Ring Compounds. J. Am. Chem. Soc. 1954, 76, 467. 49. Ahrendt, K. A.; Borths, C.J.; MacMillan, D. W. C. New Strategies for Organic Catalysis: The First Highly Enantioselective Organocatalytic Diels−Alder Reaction. J. Am. Chem. Soc. 2000, 122, 4243. 50. Hine, J.; Menon, B. C.; Mulders, J.; Flachskam, R. L Jr. Catalysis of Alpha.- Hydrogen Exchange. IX. Isobutyraldehyde-2-d exchange in the Presence of Amino Acids, J. Org. Chem. 1969, 34, 4083. 51. Wang, X. J.; Zhao, Y.; Liu, J. T. Regiospecific Organocatalytic Asymmetric Aldol Reaction of Methyl Ketones and α,β-Unsaturated Trifluoromethyl Ketones Org. Lett. 2007, 9, 1343. 52. List, B. The Direct Catalytic Asymmetric Three-Component Mannich Reaction. J. Am. Chem. 2000, 122, 9336. 53. (a) Halland, N.; Braunton, A.; Bachmann, S.; Marigo, M.; Jørgensen, K.A. Direct Organocatalytic Asymmetric α-Chlorination of Aldehydes. J. Am. Chem. 2004, 126, 4790 (b) Brochu, M. P.; Brown, S. P.; MacMillan, D. W. C. Direct and Enantioselective Organocatalytic α-Chlorination of Aldehydes. J. Am. Chem. 2004, 126, 4108. 54. Enders, D.; Grondal, C.; Hüttl, M. R. M. Asymmetric Organocatalytic Domino Reactions. Angwe. Chem., Int. Ed. 2007, 46, 1570.

140

55. Demark, S. E.; Stravenger, R. A. Asymmetric Catalysis of Aldol Reactions with Chiral Lewis Bases. Acc. Chem. Res. 2000, 33, 432. 56. Dilman, A. D.; Ioffe, S. L. Carbon−Carbon Bond Forming Reactions Mediated by Silicon Lewis Acids. Chem. Rev. 2007, 103, 733. 57. Wang, X.; Tain, S –K. Catalytic Cyanosilylation of Ketones with Simple Phosphonium Salt. Tetrahedron 2007, 48, 6010. 58. Luo, S.; Mi, X.; Zhang, L.; Liu, S.; Xu, H.; Cheng, J –P. Functionalized Chiral Ionic Liquids as Highly Efficient Asymmetric Organocatalysts for Michael Addition to Nitroolefins. Angwe. Chem., Int. Ed. 2006, 45, 3093. 59. Jensen, W. B. The Lewis acid-base Concept. Wiley, New York .1980. 60. Mukaiyama, T.; Akamatsu, H.; Hans, J. S. AConvenient Method for Stereoselective Synthesis of β-Aminoesters. Iron(II) Iodide or Trityl Hexachloroantimonate as an Effective Catalyst in the Reaction of Ketene Silyl Acetals with Imines. Chem. Lett. 1990, 889. 61. Copeland, G.T.; Elizabeth, J. R.; Miller, S. J. Minimal Acylase-Like Peptides. Conformational Control of Absolute Stereospecificity. J. Org. Chem. 1998, 63, 6784. 62. Miller, S. J. In Search of Peptide-Based Catalysts for Asymmetric Organic Synthesis. Acc. Chem. Res. 2004, 37, 601. 63. Huang, Y.; Unni, A. K.; Thadani, A. N.; Rawal, V. H. Hydrogen Bonding: Single Enantiomers from a Chiral-alcohol Catalyst. Nature 2003, 424, 146. 64. Doyle, A. G.; Jacobsen, E. N.Small-Molecule H-Bond Donors in Asymmetric Catalysis. Chem. Rev. 2007, 107, 5713. 65. Inokuma, T.; Hoashi, Y.; Takemoto, Y. Thiourea-Catalyzed Asymmetric Michael Addition of Activated Methylene Compounds to α,β-Unsaturated Imides: Dual Activation of Imide by Intra- and Intermolecular Hydrogen Bonding. J. Am. Chem. Soc. 2006, 128, 9413. 66. Akiyama, T.; Itoh, J.; Yokota, K.; Fuchibe, K. Enantioselective Mannich-Type Reaction Catalyzed by a Chiral Brønsted Acid. Angwe. Chem., Int. Ed. 2004, 43, 1566. 67. Uraguchi, D.; Terada, M. Chiral Brønsted Acid-Catalyzed Direct Mannich Reactions via Electrophilic Activation. J. Am. Chem. 2004, 126, 5156.

141

68. Unni, A. K.; Takenaka, N.; Yamamoto, H.; Rawal, V. HAxially Chiral Biaryl Diols Catalyze Highly Enantioselective Hetero-Diels−Alder Reactions through Hydrogen Bonding. J. Am. Chem. Soc. 2005, 127, 1336. 69. McDougal, N.T.; Schaus, S.EAsymmetric Morita−Baylis−Hillman Reactions Catalyzed by Chiral Brønsted Acids. J. Am. Chem. Soc. 2003, 125, 12094. 70. Nakashima, D.; Yamamoto, H. Design of Chiral N-Triflyl Phosphoramide as a Strong Chiral Brønsted Acid and Its Application to Asymmetric Diels−Alder Reaction. J. Am. Chem. Soc. 2006, 128, 9626. 71. Hashimoto, T.; Maruoka, K. Design of Axially Chiral Dicarboxylic Acid for Asymmetric Mannich Reaction of Arylaldehyde N-Boc Imines and Diazo Compounds. J. Am. Chem. Soc. 2007, 129, 10054. 72. Cleland, W. W.; Frey, P. A.; Gerlt, J. A. The Low Barrier Hydrogen Bond in Enzymatic Catalysis . J. Biol. Chem. 1998, 273, 25529. 73. Duhamel, L.; Duhamel, P.; Plaquevent, J.–C. Enantioselective Protonations: Fundamental Insights and New Concepts. Tetrahedron Asymmetry 2004, 15, 3653. 74. Vedesjs, E.; Kruger, A.; W. Catalytic Asymmetric Protonation of Amide Enolates: Optimization of Kinetic Acidity in the Catalytic Cycle. J. Org. Chem. 1998, 63, 2792. 75. Ishibashi, H.; Ishihara, K.; Yamamoto, H. Chem. Rev. 2002, 2, 177. 76. Li. H.; Wang, Y.; Tang, L.; Deng, L.Highly Enantioselective Conjugate Addition of Malonate and β-Ketoester to Nitroalkenes: Asymmetric C−C Bond Formation with New Bifunctional Organic Catalysts Based on Cinchona Alkaloids. J. Am. Chem. Soc. 2004, 126, 9906. 77. Matsui, K.; Takizawa, S.; Sasai, H.Bifunctional Organocatalysts for Enantioselective aza-Morita−Baylis−Hillman Reaction. J. Am. Chem. Soc. 2007, 127, 3680. 78. Morris, A. J.; Tolan, D. R. Lysine-146 of Rabbit Muscle Aldolase is Essential for Cleavage and Condensation of the C3-C4 Bond of Fructose 1,6-Bis(phosphate). Biochemistry. 1994, 33, 12291. 79. Machajewski, T. D.; Wong, C –H.; Lerner, R. AThe Catalytic Asymmetric Aldol Reaction. Angwe. Chem. Int. Ed. 2000, 39, 1352.

142

80. Fessner, W–D.; Shneider, A.; Held, H.; Sinerius, G.; Hixon, M.; Walter, C.; Schloss, J. DThe Catalytic Asymmetric Aldol Reaction. Angwe. Chem., Int. Ed. 1996, 35, 2219. 81. Bredig, G.; Fiske, P.Cinchona Alkaloids. Biochem Z. 1913, 46, 7 82. Wynberg, G.; Heider, R. Asymmetric Induction in the Alkaloid-Catalysed Michael Reaction. Tetrahedron Lett. 1975, 16, 4057. 83. Hiemstra, H.; Wynberg, H. Addition of Aromatic Thiols to Conjugated Cycloalkenones, Catalyzed by Chiral .beta.-Hydroxy amines. A Mechanistic Study of Homogeneous Catalytic Asymmetric Synthesis. J. Am. Chem. Soc. 1981, 103, 417. 84. France, A.; Guerin, D. J.; Miller, S. J.; Lectka, T. Nucleophilic Chiral Amines as Catalysts in Asymmetric Synthesis. Chem. Rev. 2003, 103, 2985. 85. Iwabuchi, Y.; Nakatani, M.; Yokoyama, N.; Hatakeyama, S. Chiral Amine- Catalyzed Asymmetric Baylis−Hillman Reaction: A Reliable Route to Highly Enantiomerically Enriched (α-Methylene-β-hydroxy) esters. J. Am. Chem. Soc. 1999, 121, 10219. 86. Wu, F.; Li, A.; Deng, L. Construction of Quaternary Stereocenters by Efficient and Practical Conjugate Additions to α,β-Unsaturated Ketones with a Chiral Organic Catalyst . Angwe. Chem., Int. Ed. 2006, 45, 947. 87. Perdicchia, D.; Jørgensen, K. A.Asymmetric Aza-Michael Reactions Catalyzed by Cinchona Alkaloids. J. Org. Chem. 2007, 72, 3565. 88. Lou, S.; Taoka, B. M.; Ting, S. E.; Shaus, S. E. Asymmetric Mannich Reactions of β-Keto Esters with Acyl Imines Catalyzed by Cinchona Alkaloids J. Am. Chem. Soc. 2005, 127, 11256. 89. Poulsen, T. B.; Alemparte, C.; Jørgensen, K. A. Enantioselective Organocatalytic Allylic Amination. J. Am. Chem. Soc. 2005, 127, 11614. 90. Li, H.; Soong, J.; Liu, X.; Deng, L. Catalytic Enantioselective C−C Bond Forming Conjugate Additions with Vinyl Sulfones J. Am. Chem. Soc. 2005, 127, 8948. 91. Li, H.; Wang, B.; Deng, L.Enantioselective Nitroaldol Reaction of α- Ketoesters Catalyzed by Cinchona Alkaloids. J. Am. Chem. Soc. 2006, 128, 732.

143

92. Wang, Y.; Li, H.;Wang, Y. Q.; Liu, Y.;Foxman, B. M.; Deng, L. Asymmetric Diels−Alder Reactions of 2-Pyrones with a Bifunctional Organic Catalyst J. Am. Chem. Soc. 2007, 129, 6364. 93. Li, H.; Wang, Y.; Tang, L.; Wu, F.; Liu, X.; Guo, C.; Foxman, B. M.; Deng, L. Stereocontrolled Creation of Adjacent Quaternary and Tertiary Stereocenters by a Catalytic Conjugate Addition. Angwe. Chem., Int. Ed. 2005, 44, 105. 94. Cooey, S. H.; Connon, S. J. Urea- and Thiourea-Substituted Cinchona Alkaloid Derivatives as Highly Efficient Bifunctional Organocatalysts for the Asymmetric Addition of Malonate to Nitroalkenes: Inversion of Configuration at C9 Dramatically Improves Catalyst Performance. Angwe., Chem., Int. Ed. 2005, 44, 6367. 95. Zu, L.; Wang, J.; Hao, L.; Xie, H.; Jian, W.; Wang, W. Cascade Michael−Aldol Reactions Promoted by Hydrogen Bonding Mediated Catalysis. J. Am. Chem. Soc. 2007, 129, 1036. 96. Hoashi, Y.; Okino, T.; Takemoto, Y. Enantioselective Michael Addition to α,β- Unsaturated Imides Catalyzed by a Bifunctional Organocatalyst. Angwe. Chem., Int. Ed. 2005, 44, 4032. 97. Okino, T.; Hoashi, Y.; Takemoto, Y. Enantioselective Michael Reaction of Malonates to Nitroolefins Catalyzed by Bifunctional Organocatalysts. J. Am. Chem. Soc. 2003, 125, 12672. 98. Pan, S.; Zhou, J.; List, B. Catalytic Asymmetric Acylcyanation of Imines. Angwe. Chem., Int. Ed. 2007, 46, 612. 99. Okino, T.; Nakamura, S.; Furukawa, T.; Takemoto, Y. Enantioselective Aza- Henry Reaction Catalyzed by a Bifunctional Organocatalyst. Org. Lett. 2004, 6, 625. 100. Mastui, K.; Takizawa, S.; Sasai, H. Bifunctional Organocatalysts for Enantioselective aza-Morita−Baylis−Hillman Reaction. J. Am. Chem. Soc. 2005, 127, 3680. 101. Wang, J.; Li, H.; Yu, X.; Zu, L.; Wang, W. Chiral Binaphthyl-Derived Amine-Thiourea Organocatalyst-Promoted Asymmetric Morita−Baylis−Hillman Reaction. Org. Lett. 2005, 7, 4293. 102. Wang, J.; Li, H.; Yu, X.; Zu, L.; Wang, W. Organocatalytic Asymmetric Michael Addition of 2,4-Pentandione to Nitroolefins. Org. Lett. 2005, 7, 4713.

144

103. Machajewski, T.D.; Wong, C –HThe Catalytic Asymmetric Aldol Reaction. Angwe. Chem., Int. Ed. 2000, 39, 1352. 104. Gijsen, H. J. M.; Qiao, L.; Fitz, W.; Wong, C –H. Recent Advances in the Chemoenzymatic Synthesis of Carbohydrates and Carbohydrate Mimetics. Chem. Rev. 1996, 96, 443. 105 Trost, B. M.; Fleming, I. Comprehensive Organic Synthesis: C.-H. Heathcock, Pergamon, Oxford, 1991, vol. 2. 106. Nicolaou, K. C.; Vourloumis, D.; Winssinger, N.; Baran, P.SThe Art and Science of Total Synthesis at the Dawn of the Twenty-First Century. Angwe. Chem., Int. Ed. 2000, 39, 44. 107. Ibrahem, I.; Cordova, ADirect Catalytic Intermolecular α-Allylic Alkylation of Aldehydes by Combination of Transition-Metal and Organocatalysis. Angwe. Chem., Int. Ed. 2006, 45, 1952. 108. Ding, Q.; Wu, J. Lewis Acid- and Organocatalyst-Cocatalyzed Multicomponent Reactions of 2-Alkynylbenzaldehydes, Amines, and Ketones. Org. Lett. 2007, 9, 4959. 109 Binder, J. T.; Crone, B.; Haug, T.T.; Menz, H.; Kirsch, S. FDirect Carbocyclization of Aldehydes with Alkynes: Combining Gold Catalysis with Aminocatalysis. Org. Lett. 2008, 10, 1025. 110. Yang, T.; Ferrali, A.; Campbell, L.; Dixon, D. J. Combination iminium, enamine and copper (I) cascade catalysis: a carboannulation for the synthesis of cyclopentenes , Chem. Commun. 2008, 2923. 111. Weix, D.J.; Hartwig, J. F. Regioselective and Enantioselective Iridium- Catalyzed Allylation of Enamines. J. Am. Chem. Soc. 2007, 129, 7720. 112. Beeson, T. D.; Mastracchio, A.; Hong, J –B.; Aston, K.; MacMillan, C. W. D. Enantioselective Organocatalysis Using SOMO Activation. Science 2007, 316, 582. 113. Chercheja, S.; Rothenbücher, T.; Eilbracht, PTandem Metal and Organocatalysis in Sequential Hydroformylation and Enantioselective Mannich Reactions. Adv. Synth. Catal. 2009, 351, 339. 114. Hamilton, G. L.; Kang, E. J.; Mba, M.; Toste, F. D. A Powerful Chiral Counterion Strategy for Asymmetric Transition Metal Catalysis. Science 2007, 317, 496.

145

115. Gorin, D. J.; Sherry, B. D.; Toste, F. D. Ligand Effects in Homogeneous Au Catalysis. Chem. Rev. 2008, 108, 3351. 116. Widenhoefer, R.A. Recent Developments in Enantioselective Gold(I) Catalysis. Chem. Eur. J., 2008, 14, 5382 (b) Kleinbeck, F.; Toste, F. D. Gold(I)- Catalyzed Enantioselective Ring Expansion of Allenylcyclopropanols. J. Am. Chem. Soc. 2009, 131, 9178. 117. Mukherjee, S.; List BChiral Counteranions in Asymmetric Transition-Metal Catalysis: Highly Enantioselective Pd/Brønsted Acid-Catalyzed Direct α- Allylation of Aldehydes. J. Am. Chem. Soc. 2007, 129, 11336. 118. Liao, S.; List, BAsymmetric Counteranion-Directed Transition-Metal Catalysis: Enantioselective Epoxidation of Alkenes with Manganese(III) Salen Phosphate Complexes. Angwe. Chem., Int. Ed. 2010, 4, 628. 119. Zhong, C.; Shi, XWhen Organocatalysis Meets Transition-Metal Catalysis. Eur. J. Org. Chem. 2010, 2999. 120. Ma, J. A.; Cahard, D. Towards Perfect Catalytic Asymmetric Synthesis: Dual Activation of the Electrophile and the Nucleophile., Angwe. Chem., Int. Ed. 2004, 43, 4566. 121. Kanai, M.; Kato, N.; Ichikawa, E.; Shibasaki, M. Power of Cooperativity: Lewis Acid-Lewis Base Bifunctional Asymmetric Catalysis. Synlett. 2005, 1491. 122. Shibasaki, M.; Matsunaga, S. Design and application of linked-BINOL chiral ligands in bifunctional asymmetric catalysis. Chem. Soc. Rev. 2006, 35, 269. 123. Paull, D. H.; Abraham, C. J.; Scerba, M. T.; Alden-Danforth, E.; Lectka, TBifunctional Asymmetric Catalysis: Cooperative Lewis Acid/Base Systems. Acc. Chem. Res. 2008, 41, 655. 124. Shibasaki, M.; Kanai, M.; Matsunaga, S.; Kumagai, N. Recent Progress in Asymmetric Bifunctional Catalysis Using Multimetallic Systems. Acc. Chem. Res. 2009, 42, 269. 125. Bahmanyar, S.; Houk, K. N.; Martin, H. J.; List, B. Quantum Mechanical Predictions of the Stereoselectivities of Proline-Catalyzed Asymmetric Intermolecular Aldol Reactions. J. Am. Chem. Soc. 2003, 125, 2475. 126. Marquez, C.; Metzger, J. O. ESI-MS study on the aldol reaction catalyzed by L-proline . Chem. Commun. 2006, 1539.

146

127. Hoang, L.; Bahmanyar, S.; Houk, K. N.; List, B., Kinetic and Stereochemical Evidence for the Involvement of Only One Proline Molecule in the Transition States of Proline-Catalyzed Intra- and Intermolecular Aldol Reactions. J. Am. Chem. Soc. 2003, 125, 16. 128. Mukherjee, S.; Yang, J. W.; Hoffmann, S.; List, B. Asymmetric Enamine Catalysis. Chem. Rev. 2007, 107, 5471. 129. MacMillan, D. W. C. The advent and Development of Organocatalysis., Nature 2008, 455, 304. 130. Shiraishi, S.; Araki, K.; Yamada, M. A New Type of Tetradentate Square- Planar N2O2 Ligands. Copper (II) Complexes of 6,6’–Bis(acylamino)-2,2’ – bipyridine. Bull. Chem. Soc. Jpn. 1987, 60, 3149. 131. Schneider, J. P.; Kelly, J. W. Sythesis and Efficacy of Square Planar Complexes Designed to Nucleate β-Sheet Structures. J. Am. Chem. Soc. 1995, 117, 2533. 132. Tiliakos, M.; Cordopatis, P.; Terzis, A.; Raptopoulou, C. P.; Perlepes, S. P.; Manessi-Zoupa, E., Reactions of 3d-Metal Nitrates with N,N '-bis(2-pyridyl)urea (LH2): Preparation, X-ray Crystal Structures and Spectroscopic Studies of the Products Trans-[M(II)(ONO2)(2)(LH2)(2)] (M=Mn, Fe, Co, Ni, Cu, Zn) and mer- [Co(III)(LH)(2)](NO3) Center Dot MeOH. Polyhedron 2001, 20, 2203. 133. Mukherjee, S.; Yang, J. W.; Hoffmann, S.; List, B., Asymmetric Enamine Catalysis. Chem. Rev. 2007, 107, 5471. 134. Trost, B. M.; Brindle, C. S., The Direct Catalytic Asymmetric Aldol Reaction. Chem. Soc. Rev. 2010, 39, 1600. 135. Notz, W.; List, B Asymmetric Synthesis of anti- 1, 2–Diols. J. Am. Chem. Soc. 2000, 122, 7387. 136. Jen, W. S.; Wiener, J. J. M.; MacMillan, D. W. C. New Strategies for Organo Catalysis: The first Enantiomeric Organocatalytic 1, 3 –Dipolar Cycloaddition. J. Am. Chem. Soc. 2000, 122, 9874. 137. Barbas, F. C., Organocatalysis Lost : Modern Chemistry, Ancient Chemistry, and Unseen Biosynthetic apparatus. Angwe. Chem., Int. Ed. 2008, 47, 42. 138. Dondoni, A.; Massi, A. Asymmetric Organocatalysis: From Infancy to Adolescence. Angwe. Chem., Int. Ed. 2008, 47, 4638.

147

139. Melchiorre, P.; Marigo, M.; Carlone, A.; Bartoli, G. Asymmetric Aminocatalysis: Gold Rush in Organic Chemistry. Angwe. Chem., Int. Ed. 2008, 47, 6138. 140. Mase, F.; Tanaka, F.; Barbas, F.C.Synthesis of β –hydroxylaldehyde with Stereogenic Quanternary Carbon Center by Direct Organocatalytic Asymmetric aldol reaction. Angwe. Chem., Int. Ed. 2004, 43, 2420. 141. Wang, W.; Li, H.; Wang, J. Direct, Pyrrolidine Sulfonamide promoted Enantioselective aldol Reaction of αα Dialkyl aldehydes: Synthesis of Quanternary Carbon containing β –hydroxyl Carbonyl Compounds. Tetrahedron Lett. 2005, 46, 5077. 142. Tang, Z.; Yang, Z –H.; Cheng, X –H.; Cun, L –F.; Mi, A –Q.; Jiang, Y –Z.; Gong, L –Z. Highly Efficient Organocatalyst for Direct Aldol reaction of Ketones and Aldehydes. J. Am. Chem. Soc. 2005, 127, 9285.

143. Samanta, S.; Liu, J –Y.; Dodda, R.; Zhao, C–G. C2–Symmetric Bisprolinamide as a highly Efficient catalyst for Direct aldol reaction. Org. Lett. 2005, 7, 5321. 144 Krattiger, P.; Kovasy, R.; Revell, D, J.; Ivan, S.; Wennemers, H. Increased Structural Complexity Leads to Higher Activity: Peptides as Efficient and Versatile Catalyst for Asymmetric Aldol Reaction. Org. Lett. 2005, 7, 1101 145. Wu, Y –Y.; Zhang, Y –Z.; Yu, M –L.; Zhao, G.; Wang, S –W. Highly Efficient and ReusableDendritic Catalyst Derived from N–Prolylsulfonamide for the Asymmetric Direct Aldol Reaction in water. Org. Lett. 2006, 8, 4417. 146. Mase, N.; Nakai, Y.; Ohara, N.; Yoda, H.; Takabe, K.; Tanaka, F.; Barbas, C. F. Organocatalytic Direct Asymmetric Reaction in Water. J. Am. Chem. Soc. 2006, 128, 734. 147. Hiyashi, Y.; Sumiya, T.; Takahashi, J.; Gotoh, H.; Urushima, T.; Shoji, M. Highly Diastereo-and Enatioselective Aldol Reaction in Water. Angwe. Chem., Int. Ed. 2006, 45, 958. 148. D’Elia, V.; Zwicknagel, H.; Reiser, OShort α,β-Peptides as Catalysts for Intra- and Intermolecular Aldol Reactions. J. Org. Chem. 2008, 73, 3262. 149. Yang, H.; Carter, R. G. N–(p–Dodecylphenylsulfonyl)-2-pyrrolidine carboxamide : A Practical Proline Mimetic for Fascilitating Enantioselective Aldol Reaction. Org. Lett. 2008, 10, 4649.

148

150. Hayashi, Y.; Itoh, T.; Aratake, S.; Ishikawa, H.; A Diarylprolinol in an Asymmetric, Catalystic, and Direct Crossed–Aldol Reaction of Acetaldehydes. Angwe. Chem., Int. Ed. 2008, 47, 2082. 151 Wang, W.; Wang, J.; Li, H.; Xie, H.; Zu, L. Highly Enantioselective Organocatalytic Conjugate Addition to α,β-Unsaturated Aldehydes: Three–step Synthesis of Optically Active Baclofen. Adv. Synth. Catal. 2007, 349, 2660. 152. Wang, F.; Xiong, Y.; Liu, X. H.; Feng, X. M. Asymmetric Direct Aldol Reaction of α-Keto Esters and acetone Catalyzed by Bifunctional Catalyst. Adv. Synth. Catal. 2007, 349, 2665. 153. Liu, J.; Yang, Z. G.; Wang, Z.; Wang, F.; Chen, X. H.; Liu, X. H.; Feng, X. M.; Su, Z. S.; Hu, C, W. Asymmetric Direct Aldol Reaction of Functionalized Ketones Catalyzed by Amine Organocatalysts based on Bispidine. J. Am. Chem. Soc., 2008, 130, 5654. 154. Yu, X.; Wang, W. Organocatalysis: Asymmetric Cascade Reaction Catalyzed by Chiral Secondary Amine. Org. Biomol. Chem. 2008, 6, 2037. 155. Parks, J. E.; Wagner, B. E.; Holm, R. H. Synthesis Employing Pyridyllithium Reagents: New routes to 2,6–Disubstituted Pyridines and 6, 6’–Disubstituted 2, 2’- Bipyridyls. J. Organomet. 1973, 56, 53. 156. Sleebs, M. M.; Hughes, A. B.; Brownlee, R. T. C.; Box, J. S.; Aurelio, L. An Efficient Synthesis of N–Methyl Amino acids by way of Intermediate 5 –oxazalo. J. Org. Chem. 2003, 68, 2652. 157. Xu, Z.; Daka, P.; Budik, I.; Wang,H.; Bai, F –Q.; Zhang, H –X. Enamine- Metal Lewis Acid Bifunctional Catalysis: Apllication to Direct Asymmetric Aldol Reaction of Ketones. Eur. J. Org. Chem. 2009, 4581. 158. Xu, Z.; Daka, P.; Wang, H. Primary Amine-Metal Lewis acid Bifunctional Catalysts: the Application to Asymmetric Direct Aldol Reaction. Chem. Commun. 2009, 6825. 159. Sakthivel, K. S.; Notz, W.; List, B. Amino Acid Catalyzed Direct Asymmetric Aldol Reaction: A Bioorganic Approach to Catalytic Asymmetric Carbon-Carbon bond–Formation Reaction . J. Am. Chem. 2001, 123, 5260. 160. Xu, L –W.; Lu, Y. Primary Amino Acid: Privilaged Catalysts in Enantionselective Organocatalysis. Org. Biomol. Chem. 2008, 6, 2047. 161. Xu, L –W.; Luo, J.; Lu, Y Asymmetric Catalysis with Chiral Primary Amine –Based Organocatalysts. Chem. Commn. 2009, 1807. 149

162. Amedjkouh, M.; Primary Amine Catalyze Direct Asymmetric Aldol Reaction in Water. Tetrahedron: Asymmetry 2005, 16, 1411. 163. Cordova, A.; Zou, W –B.; Ibrahem, I.; Reyes, E.; Engqvist, M.; Liao, W –W. Acyclic Amino Acid –Catalyzed Direct Asymmetric Aldol Reactions: Alanine, the Simplest Stereoselective Organocatalyst. Chem. Commn. 2005, 3586. 164. Jiang, Z.; Liang, Z.; Xu, X.; Lu, L. Asymmetric Aldol Reactions Catalyzed by Triptophan in Water. Chem. Commn. 2006, 2801. 165. Wu, X.; Jiang, Z.; Shen, H –M.; Lu, Y. Highly Efficient Threonine–Direved Organocatalyst for Direct Asymmetric Aldol Reactions in Water. Adv. Synth. Catal. 2007, 349, 812. 166. Luo, S.; Xu, H.; Li, J.; Zhang, L.; Cheng, J –P. Simple Primary –Tertiary Diamine –Brønsted Acid Catalysts for Asymmetric Direct Aldol Reactions for Linear Aliphatic Ketones. J. Am. Chem. Soc. 2007, 129, 3074. 167. Xu, X –Y.; Wang, Y –Z.; Gong, L –Z. Design of Organocatalyst for Asymmetric Direct Syn –Aldol Reactions. Org Lett. 2009, 9, 4247. 168. Nakayama, K.; Maruoka, K.; Complete Switch of Product Selectivity in Asymmetric Direct Aldol Reactions with different Chiral Organocatalysts from a Common Source. J. Am. Chem. Soc. 2008, 130, 3074. 169. Cheng, L.; Hang, X.; Huang, H.; Wong, M. W.; Lu, Y. Highly Diastereoselective and Enantioselective Direct Organocatalytic anti –Selective Mannich Reactions Employing N –tosylimines. Chem. Commun. 2007, 4143. 170. Ramasastry, S. S. V.; Zhang, H. L.; Tanaka, F.; Barbas III, C. F. Direct Catalyzed Asymmetric Synthesis of anti -1,2 Amino Alcohols and Syn 1,2 –Diols through Organocatalytic anti –Mannich and syn –Aldol Reactions. J. Am. Chem. Soc. 2007, 129, 288. 171. Ibrahem, I.; Zou, W.; Engqvist, M.; Xu, Y.; Córdova, A. Acyclic Chiral Amines and Amino Acids as Inexpensive and Readily Tunable Catalysts for the Three –Component Mannich Reactions. Chem. –Eur. J. 2005, 11, 7024 172. Daka, P.; Xu, Z.; Alexa, A.; Wang, H. Primary Amine –Metal Lewis Acid Bifunctional Catalysts based on a Simple Bidentate Ligand: Direct Asymmetric Aldol Reaction. Chem. Commun. 2011, 47, 224. 173. Peng, F. Z.; Shao, Z. H. Advances in Asymmetric Organocatalytic Reactions Catalyzed by Chiral Primary Amines. J. Mol. Catal. A. Chem. 2008, 285, 1.

150

174. Zheng, B. L.; Liu, Q. Z.; Guo, C. S.; Wang, X. L.; He, L. Highly Enantionselective Direct Aldol Reaction Catalyzed by Cinchona derived Primary Amine. Org. Biomol. Chem. 2007, 5, 2913. 175. Zeidan,R. K.; Davis, M. E. The Effects of Acid-Base pairing on Catalysis: An efficient Acid-Base Functionalized Catalysts for Aldol Condensation. J. Catal. 2007, 247, 379. 176. Luo, S. Z.; Zheng, X. X.; Cheng, J. P. Asymmetric Bifunctional Primary Aminocatalysts on Magnetic Nanoparticle. Chem. Commun. 2008, 5719. 177. Peng, F. Z.; Shao, Z. H.; Pu, X. W.; Zhang, H. B. Highly Diastereo –and Enantioselective Direct Aldol Reactions Promoted by Water-Compatible Organocatalysts Bearing Central and Axial Chiral Elements. Adv. Synth. Catal. 2008, 350, 2199. 178. Li, J. Y.; Luo, S. Z.; Cheng, J. P. Chiral Primary–Tertiary Diamine Catalysts Derived From Natural Amino Acids for Syn–Aldol Reactions of Hydroxy Ketones J. Org. Chem. 2009, 74, 1747 179. Luo, S. Z.; Xu, H.; Zhang, L.; Li, Y.; Cheng, J. P. Highly Enantioselective syn –and anti –Aldol Reactions of Dihydroxyacetone Catalyzed by Chiral Primary Amines Catalysts. Org. Lett. 2009, 74, 1747. 180. Ma, x.; Da, C. S.; Yi, L.; Jia, Y. N.; Guo, Q. P.; Che, L. P.; Wu, F. C.; Wang, J. R.; Li, W. P. Highly Efficient Primary Amine Organocatalysts for the Direct Asymmetric Aldol Reaction in Brine. Tetrahedron: Asymmetry 2009, 20, 1419. 181. Zhou, J.; Wakchaure, V.; Kraft, P.; List, B. Primary –Amine Catalyzed Enantioselective Intramolecular Aldolizations. Angwe. Chem., Int. Ed. 2008, 47, 7656. 182. Cordova, A.; Zou, W. B.; Dziedzic, P.; Ibrahem, I.; Reyes, E.; Xu, Y. M. Direct Asymmetric Intermolecular Aldol Reactions Catalyzed by Amino Acids and Small Peptides. Eur. J. Org. Chem. 2006, 5383. 183. Hughes, C. C.; Trauner, D. The Total Synthesis of (-) –Amathaspiramide F. Angew. Chem., Int. Ed. 2002, 45, 1234. 184. Chemg, X.; Vellalath, S.; Goddard, R.; List, B. Direct Catalytic Asymmetric Synthesis of Aminals from Aldehydes J. Am. Chem. Soc. 2008, 130, 15786. 185. Schneider, G., and Fechner, U. Computer Based de nova Design of Drug – Like Molecules. Nat. Rev. Drug Discovery 2005, 4, 649.

151

186. Mhaske, S. B.; Argade, N. P.The Chemistry of Recently Isolated Naturally Occurring Quinazolinone Alkaloids Tetrahedron 2006, 62, 9787. 187. Baldwin, S. W.; Long, A. 2–tert-Butyl -3-Methyl-2,3–dihdyroimidazol -4- one-N–oxide: A New Nitrone–Based Chiral Glycine Equivalent. Org. Lett. 2004, 6, 1653. 188. Methot, J. L.; Dunstan, T. A.; Mamprelan, D. M.; Adams, B.; Altman, M. D. Unexpected Aminocyclopropane Reductive Rearrangement. Tetrahedron Lett. 2008, 49, 1155. 189. Jung, M. E.; Huang, A. Use of Optically Active Cyclic N, N–Dialkyl Aminals in Asymmetric Induction. Org. Lett. 2000, 2, 2659. 190. Yang, J. W.; Fonseca, M. T. H.; List, B. Catalytic Asymmetric Reductive Michael Cyclization . J. Am. Chem. Soc. 2005, 127, 15036. 191. Uozumi, Y.; Shibatomi, K. Catalytic Asymmetric Allylic Alkylation in Water with a Recyclable Amphiphilic Resin-Supported P, N–Chelating Palladium Complex. J. Am. Chem. Soc. 2001, 123, 2919. 192. Uozumi, Y.; Yasoshima, K.; Miyachi, T.; Nagai, S. Enantioselective Desymmetrization of Meso –cyclic Anhydride Catalyzed by Hexahydro -1H – Pyrrolol [1, 2 –c] Imidazolones. Tetrahedron Lett. 2001, 42, 411. 193. Ouellet, S. G.; Tuttle, J. B.; MacMillan, D. W. C. Enantioselective Organocatalytic Hydride Reduction. J. Am. Chem. Soc. 2005, 127, 32. 194. Takenaka, K.; Uozumi, Y. An N–C–N Pincer Palladium Complex as an Efficient Catalyst Precursor for the Heck Reaction . Adv. Synth. Catal. 2004, 346, 1693. 195. Uozumi, Y.; Mizutani, K.; Nagai, S.A Parallel Preparation of a Bicyclic N – Chiral Amine Library and its use for Chiral Catalyst Screening. Tetrahedron Lett. 2001, 42, 407. 196. Chan, B. K. H.; Deng, B.; Jones, M. W.; Read, R. W. An Efficient Method for the Preparation of mono–Alkyl derivatives of 1,1’ –bis(6, 7 –dimethoxy -1,2,3,4 – tetrahydroisoquinoline) Tetrahedron 2006, 62, 4979. 197. Zhang, C.; Murarka, S.; Seidel, D. Facile Formation of Cyclic Aminals through a Bronsted Acid Promoted Redox Process. J. Org. Chem. 2009, 74, 419.

152

198. Polshettiwar, V.; Varma, R. S Ring –Fused Aminals: Catalyst and Solvent – Free Microwave –Assisted α. –amination of Nitrogen Heterocyles. Tetrahedron Lett. 2008, 49, 7165. 199. Moss, W. O.; Jones, A. C.; Wisedale, R.; Mahon, M. F.; Molloy, K. C.; Bradbury, R. H.; Hales, N. J.; Gallagher, T.2–Aminoketene S, S–Acetals as α– Amino acid Homoenolate Equivalents: Synthesis of 3 –Substituted Prolines and Molecular Structure of 2 –(N –pivaloylpyrrolidin -2ylidine) -1, 3 dithiane J. Chem. Soc. Perkin Trans. 1 1992, 2615. 200. Federsel, H. J.; Konberg, E.; Lilljequist, L.; Swahn, B. M. Dichloromethane as Reactant in Synthesis: An expedient Transformation of Prolinamide to a novel Pyrrolol [1, 2 –c] imidazolone. J. Org. Chem. 1990, 55, 2254. 201. Rowland, G. B.; Zhang, H. L.; Rowland, E. B.; Chennamadhavuni, S.; Wang, Y.; Antilla, J. C. Bronsted Acid -Catalyzed Imine Imidation. J. Am. Chem. Soc. 2005, 127, 15696. 202. Zhang, C.; De, C. K.; Mal, R.; Seidel, D. α –Amination of Netrogen Heterocyles: Ring –Fused Aminals. J. Am. Chem. Soc. 2008, 130, 416. 203. Shibatomi, K.; Uozumi, Y. New Homochiral Phosphine Ligands having a Hexahydro -1H –pyrrolol[1, 2, -c] imidazoloneBackbone: Preparation and use of Palladium-Catalyzed Asymmetric Alkylation of Cycloalkenyl Carbonates. Tetrahedron Asymmetry 2002, 13, 1769. 204. Koch, K.; Schweizer, W. B.; Eschenmoser, A. Reaction of HCN–Tetramer with Aldehydes. Chem. Biodivers. 2007, 4, 541. 205 Che, X.; Zheng, L. Y.; Dang, Q.; Bai, X. Synthesis of 7,8,9 –Trisubstituted Dihdropurine Derivatives via a ‘tert –Amino Effect’ Cyclization. Synlett. 2008, 2373. 206. Zhang, Y. M.; Fu, H.; Jiang, Y. Y.; Zhao, Y. F. Copper–Catalyzed Amidation of Sp3 C–H Bonds Adjacent to a Nitrogen Atom. Org. Lett. 2007, 9, 3813. 207. Liang, Y.; Rowland, E. B.; Rowland, G. B.; Perman, J. A.; Antilla, J. C.VAPOL Phosphoric Acid Catalysis: The Highly Enantioselective Addition of Imides to Imines. Chem. Commun. 2007, 4477. 208. Li, G. L.; Fronczek, F. R.; Antilla, J. C Catalytic Asymmetric Addition of Alcohols to Imines: Enantioselective Preparation of Chiral N, O -Aminals. J. Am. Chem. Soc. 2008, 130, 12216.

153

209. Trost, B. M.; Brindle, C. S., The Direct Catalytic Asymmetric Aldol Reaction. Chem. Soc. Rev. 2010, 39, 1600. 210. Cergol, K. M.; Turner, P.; Coster, M. J., The boron-mediated ketone-ketone aldol reaction. Tetrahedron Lett. 2005, 46, 1505. 211. Denmark, S.E.; Fan, Y. Catalytic, Enantioselective Aldol Additions to Ketones. J. Am. Chem. Soc. 2002, 124, 4233. 212. Adachi, S.; Harada, T.; Catalytic Enantionselective Aldol Additions of Ketones. Eur. J. Org. Chem. 2009, 3661.

213. Yoshida, Y.; Hayashi, R.; Sumihara, H.; Tanade, Y. TiCl4/Bu3N(Catalytic TMSOTf): Efficient Agent of Direct Aldol Addition and Claisen Condensation. Tetrahedron Lett. 1997, 38, 8727. 214. Koech, P. K.; Krische, M. J., Catalytic addition of metallo-aldehyde enolates to ketones: A New C-C Bond-Forming Hydrogenation. Org. Lett. 2004, 6, 691. 215. Enders, D.; Grondal, C., Direct Organocatalytic de novo Synthesis of Carbohydrates. Angew. Chem., Int. Ed. 2005, 44, 8, 1210. 216. Suri, J. T.; Mitsumori, S.; Albertshofer, K.; Tanaka, F.; Barbas, C. F., Dihydroxyacetone Variants in the Organocatalytic Construction of Carbohydrates: Mimicking Tagatose and Fuculose Aldolases. J. Org. Chem. 2006, 71, 3822. 217. Oisaki, K.; Zhao, D.; Kanai, M.; Shibasaki, M., Catalytic Enantioselective Aldol Reaction to Ketones. J. Am. Chem. Soc. 2006, 128, 7164. 218. Curti, C.; Sartori, A.; Battistini, L.; Rassu, G.; Buffeddu, P.; Zanardi, F.; Casiraghi, G., Vicarious Silylative Mukaiyama Aldol Reaction: A Vinylogous Extension. J. Org. Chem. 2008, 73, 5446. 219. Bernard, A. M.; Frongia, A.; Piras, P. P.; Secci, F.; Spiga, M., Synthesis of Enantiomerically Enriched Secondary and Tertiary Phenylthio-and Phenoxy- Aldols. Tetrahedron Lett. 2008, 49, 3037. 220. Shiomi, T.; Nishiyama, H., Intermolecular Asymmetric Reductive Aldol Reaction of Ketones as Acceptors Promoted by Rh (phebox) Catalyst. Org. Lett. 2007, 9, 1651. 221. Liu, J.; Yang, Z. G.; Wang, Z.; Wang, F.; Chen, X. H.; Liu, X. H.; Feng, X. M.; Su, Z. S.; Hu, C. W., Asymmetric Direct Aldol Reaction of Functionalized Ketones Catalyzed by Amine Organocatalysts Based on Bispidine. J. Am. Chem. Soc. 2008, 130, 5654.

154

222 Alfini, R.; Cecchi, M.; Giomi, D., Reactivity and Synthetic Applications of 4,5 Dicyanopyridazine : An Overview. Molecules .2010, 15, 1722 223. Berkessel, A.; Adrio, J. A. Dramatic Acceleration of Olefin Epoxidation in Fluorinated Alcohols: Activation of Hydrogen peroxide by Multiple H-Bond Network. J. Am. Chem. Soc. 2006, 128, 13412. 224. Arai, T.; Yokoyama, N. Tandem Catalytic Asymmetric Friedel–Crafts/Henry Reactions: Control of Three–Contiguous Acyclic Stereocenter. Angwe. Chem., Int. E. 2008, 47, 4989. 225. Nakamura, S.; Hara, N.; Nakashima, H.; Kubo, K.; Shibata, N.; Turo, T. Enantioselective Synthesis of (R)–Convolutamydine A With N– Heteroarylsulfonylprolinamides. Chem, Eur. J. 2008, 14, 8079. 226. Chen, J –R.; Liu, X. –P.; Zhu, X –Y.; Li, L.; Qiao, Y –F.; Zhang, J –M.; Xiao, W –J. Organocatalytic Asymmetric Aldol Reaction of Isatin: Straightforward Stereoselective Synthesis of 3–alkyl-3 –hydroxylindolin -2 –ones. Tetrahedron 2007, 63, 10437. 227. Marti, C.; Carreira, E. M. Construction of Spiro[pyrrolidine -3,3’ –Oxindoles] –Recent Application to the Synthesis of Oxindole Alkaloids. Eur. J. Org. Chem. 2003, 2209

155

DESIGN AND SYTHESIS OF STAT3 INHIBITORS

2.0 Introduction

Signal Transducer and Activator of Transcription 3 (STAT3) is a transcription factor that belongs to a family of seven STAT proteins that regulate important cellular processes like cell survival, immune response, angiogenesis and cell proliferation.1-3 The STAT3 protein consists of four functional domains: coiled coil, DNA binding, SH2 dimerization, and transactivation that contributes to its oligomerization and cooperatively enable it to carry out its function (Fig.2.0.20).

Figure 2.0.20. STAT3 overall structure. 156

These proteins are activated by phosphorylation of two conserved residues, tyrosine (Tyr705) and serine (Ser727), in response to extracellular signaling by molecules such as cytokines and growth factors.4,5 Once activated, it dimerizes and translocates into the nucleus where it binds to specific promoter on the DNA and induces transcription of certain targeted genes (Fig.2.0.21).6,7 For normal functioning of the cell under physiological conditions, this process is highly regulated. However, overexpression and constitutive high levels of STAT3 are frequently detected in cancer patient’s specimens with advanced disease and in human cancer cell lines.8 Growing evidence shows that overexpression and persistent activation of the STAT3 affects ecogenesis directly by stimulating cell proliferation and inhibiting apoptosis in human cancer cells.9 Since STAT3 is a bona fide mediator to ecogenesis resulting in a lot of human malignancies, its inhibition provides a very attractive target to combat cancer. Not only does STAT3 encourage continuous cell growth but it also renders drugs that encourage apoptosis as a major pathway to combat tumors useless.

Several compounds have been developed to inhibit STAT3 through different mechanisms, thereby suppressing tumor growth and inducing apoptosis in cancer cells. Fig.2.0.21 is a schematic representation of the STAT3 signaling pathway from the cell surface to the nucleus where it initiates transcription.6 There are potentially seven different points in this pathway at which inhibitors can target STAT3 (numbers in parenthesis). As can be seen from Fig.2.0.21, the strategies can broadly be divided into two: direct STAT3 inhibition that target STAT3 protein and indirect inhibition targeting other proteins associated with STAT3 that are crucial to the pathway. Indirect inhibition involves targeting the cytokines like the Janus kinase (JAK), antisense approach, oligonucleotide siRNAs, dominant– negative mutant, decoy oligonucleotides, and G–quartet oligonucleotides that are 157

responsible for upstream activation leading to phosphorylation.10-15 Specifically, small molecules like pyridine 6, and natural product based indirubin16 and resveratrol,17 cucurbitacin analogues,18,19 and capsaicin20 have been explored in this arena. Unfortunately, most of these inhibitors suffer from a lot of shortcomings since they don’t target STAT3 directly but other upstream proteins, as a result other signaling pathways are also affected by them. Under direct strategy, dimerization has been the major focus since it constitutes the crucial step in STAT3 activation. A number of small molecule inhibitors have been designed to this end. These inhibitors generally fall into two categories:

158

159

Peptedomimics 21-24 (examples are shown in Fig.2.0.22) 25-28 and non- peptidomimics29,30 (Fig.2.0.23).

160

In vitro studies have demonstrated that peptide–based inhibitors bind strongly to STAT3 resulting in high affinities compared to their non-peptide–based analogues. However, peptide–based compounds usually suffer from low cellular permeability and the negative charges on the phosphotyrosine amino acid residues which worsens the whole scenario. On the other hand, non-peptide–based inhibitors usually have excellent cellular permeability but fall short in binding affinities, consequently they display low potency. For this reason, it is hard to attribute the cellular activity to STAT3 inhibition or something else.28 Despite tremendous effort that is being channeled in the design of STAT3 inhibitors very few of the current inhibitors have been developed to the point that they can be subjected to clinical trials.27 It is therefore imperative that new small–molecule antagonists which can inhibit STAT3 be designed and explored.

161

2.1. Design of the inhibitors

Results and Discussion

Our model compound (166a) that was discovered to possess inhibitory activities against STA3 was originally developed as a catalyst for the MBH reaction. Although it turned out to be a mediocre catalyst for the MBH reaction, it showed inhibitory activity towards STAT3 phosphorylation and caused apoptosis in human hepatocellular carcinoma cells31. A molecular docking experiment revealed that it binds to two of the three binding pockets of SH2 domain (Fig.2.1.24). A computer model predicted that interactions are via hydrogen bonding between the inhibitor and the amino acids residues Ser636, Lys591 and Arg609 of the SH2 domain (Fig 2.1.25).

Figure 2.1.24 SH2 binding pockets 1, 2 and 3 (circles) of STAT3 and the binding between 166a and STAT3 SH2.

162

Figure 2.1.25 Computer model showing interaction between STAT3 (smaller sticks/ribbons) and 166a (larger sticks) via hydrogen bonds (dotted lines). Encouraged by these results we designed and synthesized a number of 166a analogues to study the structure activity relationships (SARs) of 166a generating (Fig.2.1.26).

The synthesis of these inhibitors follows a general route which begins with L- Histidine. L-histadine undergoes a series of transformation to generate the alkyl 2- amino (1–alkyl-1H–imidazol-4–yl) propanoate which serves as the major starting materials for subsequent coupling reactions. The N–alkyl histidine alkyl ester is coupled to an appropriate N-Boc protected amino acid followed by another coupling with 1–isocyanato-3, 5–bis(trifluoromethyl) benzene after deprotection of the Boc group (Scheme 2.1.50).

163

Using this protocol, 16 inhibitors (Figure 2.1.26) were synthesized and their activities on different cell lines were evaluated (Table 2.1.33).

164

Figure 2.1.26 Inhibitors synthesized.

165

Entry Inhibitor PANC-1 HPAC MDA-MB-231 SW1990

1 166a 24.7 17.4 15.5 17.9

2 166b 50-100 ND ND ND

3 166c 16.8 13.2 10.6 9.1

4 166d 10.1 7.6 6.5 8.3

5 166e >100 ND ND ND

6 166f >100 ND ND ND

7 166g 16.1 9.6 6.8 10.8

8 166h 31.4 ND ND ND

9 166i 68.6 ND ND ND

10 166j 85.5 ND ND ND

11 166k 11.1 9.5 7.6 9.4

12 166l 8.8 9.8 9.4 8.5

13 166m 61.9 ND ND ND

14 166n 98.4 ND ND ND

15 167 29.6 ND ND ND

Table 2.1.33 IC50 (µM) values in different cancer cell lines.

166

Figure 2.1.27 Showing the three parts that we focused on SAR.

The structure of the inhibitor can be broken into three parts: the head imidazole (A), the core (B) and the tail benzene (C) (Fig.2.1.27). The study of structure activity relationships (SARs) started with checking if the two trifluoromethyl groups on the benzene ring are crucial to the activity of the inhibitor. We therefore synthesized 166m carrying only one trifluoromethly group. The IC50 of 166m was 61.9µM against pancreatic cancer cell lines worse than that of 166a (24.7 µM) (Table 2.1.33 entries 1 and 13). It suggests that two trifluoromethyl groups are needed to attain high inhibitory’s activity.

We then synthesized 167 that carries no imidazole ring. 167 gave IC50 of 29.6 µM, again worse than 166a suggesting that the imidazole ring is crucial (entry 14). Interestingly, 166n that bears an imidazole ring carrying no substituent on the τ nitrogen, displayed poor results compared to 166a and 167 (entry 1, 14 and 15), suggesting that not only is the imidazole ring crucial to attain higher activity but it should bear a substitute on the τ nitrogen. We then hydrolyzed the ester group on the histidine moiety of 166a and 166b generating a free carboxylic acid to give 166e and 166f. Inhibitory activity of 166a and 166b significantly went down with

IC50 value greater than 100 µM (entry 5 and 6). We then synthesized 9 different

167

inhibitors utilizing different amino acids that resulted in inhibitors with varying R3 groups (Scheme 2.1.50). As shown in Table 2.1.33, the more bulky R3 group 3 becomes, the better the activity. For example, when R = methyl group the IC50 is 3 50-100 µM and when R =tert-butyl group the IC50 decreased to 8.8 µM (entries 2 and 12 respectively). Other compounds having varying lengths of the R3 were made (entries 1, 3, 4 and 12). Since we had demonstrated that the imidazole ring has to be τ nitrogen substituted for higher activity, we reasoned that there should be a correlation between the size of the substituent and the activity. We then made 166k which has an ethyl group at the τ position. Amazingly, the activity improved to 11.1 µM (entry 11), much better than that of 166a.

It should be noted that all the inhibitors made so far are expected to bind only pockets1 and 2 of the SH2 domain of the STAT3, similar to 166a which has been predicted by the molecular docking (Fig 2.1.25).

In an effort to develop small molecule inhibitors that can bind pocket 3 (Fig. 2.1.23), of the SH2 domain, we synthesized 166i and 166j with R3bearing a longer carbon chain. Disappointingly, 166i and 166j showed much worse results with IC50 values of 68.6 µM and 85.5 µM, respectively (entries 9 and 10). We suspect that the incorporation of the longer carbon chain of R3 loosened the binding of the inhibitor to pocket 1 and 2 and it is very much likely that binding to pocket 3 did not occur. Based on the data obtained thus far, we can conclude that increasing the bulkiness of R1 and R3 increases the effectiveness of the inhibitors (entries 4, 11, and 12). For this reason we decided to introduce some aromatic substituents at the R3 position to take advantage of the hydrophobic factors that seemed to be at play. 3 We made 166g that carries a benzyl group at R position which gave an IC50 of

168

16.1µM (entry 7). However, introduction of an indole moiety at the same position had detrimental effects (entry 8).

In summary, the SARs that we have carried out on the original hit 166a, shows our effort in trying to convert this compound into a potent STAT3 inhibitor. Thus far, 166d and 166l shows the best potency in a variety of cancer cell lines explored.

169

Experimental for 2.1

Alkyl 2-amino-3-(1-alkyl-1H-imidazol-4-yl)propanoate (168a)

The method followed is based on the reported procedure by Cohen et al32

Methyl2-((S)-2-(3-(3,5-bis(trifluoromethyl)phenyl)ureido)-3- methylbutanamido)-3-(1-methyl-1H-imidazol-4-yl)propanoate(166a)

N-Boc-L-valine (520 mg, 4.1 mmol) in CH2Cl2 (100 mL), methyl 2-amino-3-(1- methyl-1H-imidazol-4-yl) propanoate (512mg, 4.1 mmol), DCC (494mg, 2.4 mmol), HoBt (2.4mmol, 367mg) and TEA (1mL, 8 mmol) were charged in a flask and stirred at room temperature for 3days by the time TLC showed no starting material. The reaction mixture was filtered and the filtrate was washed with aqueous NaHCO3. The organic phase was evaporated under reduced pressure and purified by column chromatography (eluent DCM/methanol, v/v, 50/1) to afford a white solid product. This was then treated with DCM/TFA (3/1) and stirred overnight to obtain an oily yellowish product. This Boc deprotected product (597mg, 1.8mmol), 1–isocyanato-3, 5–bis(trifluoromethyl) benzene (358.2mg, 1.4mmol) and 1ml of TEA were charged in flask containing 15ml DCM and stirred at room temperature overnight at which time TLC showed no starting material.

The mixture was washed with aqueous NaHCO3 and the organic layer was concentrated under reduced pressure. The resulting yellowish solid was purified by column chromatography (DCM/methanol, v/v, 30/1) to give a white solid product 300mg.

170

1 H NMR (500 MHz, CDCl3) δ 0.83- 0.91 (m, 6H), 1.98- 2.50 (m, 1H), 2.80 (m, 1H), 3.50 (s, 3H), 3.58(s, 3H), 4.15- 4.18 (m, 1H), 4.47- 4.52(m, 1H), 6.54(d, J= 8.5Hz, 1H), 6.86 (s, 1H), 7.42 (s, 1H), 7.56(s, 1H), 8.00(s, 2H), 8.51 (d, J = 7Hz, 13 1H), 9.41(s, 1H). C NMR (125Hz, CDCl3) δ 18.0, 19.2, 29.0, 31.6, 33.2, 52.2, 53.2, 59.1, 114.8, 118.0, 118.1, 122.2, 124.4,131.5, 131.8, 137.0, 137.6, 141.3, 155.2, 171.4, 173.7. MS(ESI) 538.1 (M+H)+

Methyl 2-((S)-2-(3-(3,5-bis(trifluoromethyl)phenyl)ureido)propanamido)-3- (1-methyl-1H-imidazol-4-yl)propanoate (166b)

1 H NMR (500 MHz, CDCl3) δ 1.24 (d, J =6.6Hz, 3H), 2.76- 2.590 (m, 2H), 3.53- 3.60 (m, 6H), 4.24- 4.28 (m, 1H), 4.46- 4.48 (m, 1H), 6.67(d, J = 7.2Hz, 1H), 6.85(s, 1H), 7.41 (s, 1H), 7.55 (s, 1H), 8.01 (s, 2H), 8.48 (d, J= 7.5Hz, 1H), 9.40 (s, 13 1H). C NMR (125Hz, CDCl3) δ 19.6, 30.2, 33.0, 33.3, 52.5, 52.8, 117.5, 118.3, 118.4, 122.7, 124.9, 130.8, 131.0, 131.3, 137.3, 142.8, 154.5, 172.4, 173.0. MS(ESI) 510.2 (M+H)-

171

Methyl 2-((S)-2-(3-(3,5-bis(trifluoromethyl)phenyl)ureido)-4- methylpentanamido)-3-(1-methyl-1H-imidazol-4-yl)propanoate (166c)

1 H NMR (500 MHz, CDCl3) δ 0.94- 0.96 (m, 6H), 1.51- 1.58 (m, 1H), 1.62- 165 (m, 1H),1.67-1.81 (m, 1H), 3.12- 3.13 (m, 2H), 3.58(s, 3H),3.67 (s, 3H), 4.40- 4.44 (m, 1H), 4.72- 4.75(m, 1H), 6.69-6.71 (m, 1H), 6.76 (m, 1H),7.28 (S, 1H), 7.37(s, 13 1H), 7.73 (m, 2H), 8.21- 8.23 (m, 1H), 8.44(s, 1H). C NMR (125Hz, CDCl3) δ 21.9, 22.8, 24.7, 28.9, 33.3, 41.9, 52.3, 52.6, 52.9, 117.7, 118.3, 122.2, 124.4, 131.2, 131.5, 131.7, 132.0, 136.7, 137.5, 141.2, 154.9, 171.4, 175.1. MS(ESI) 552.2 (M+H)+

Methyl 2-((S)-2-(3-(3,5-bis(trifluoromethyl)phenyl)ureido)-3,3- dimethylbutanamido)-3-(1-methyl-1H-imidazol-4-yl)propanoate (166d)

1 H NMR (500 MHz, CDCl3) δ 1.00 (s, 3H), 1.01 (s, 3H), 1.12- 1.29 (m, 1H), 1.55- 1.60 (m, 1H), 1.81- 1.84 (m, 1H), 3.07- 3.08 (m, 2H), 3.56 (s, 3H), 3.64(s, 3H), 4.35- 4.38 (m, 1H), 4.69- 4.72(m, 1H), 6.69(s, 1H), 7.24- 7.33 (m, 2H), 7.08 (s, 13 2H), 8.29- 8.30 (m, 1H), 8.44 (s, 1H). C NMR (125Hz, CDCl3) δ 11.2, 15.4,25.0, 28.9, 33.3, 37.9, 52.3, 53.2, 58.5, 114.9, 118.0, 118.2, 122.2, 124.4, 131.3, 131.8, 131.6, 131.8, 132.1, 136.8, 137.6, 141.3, 155.1, 171.2, 173.7. MS(ESI) 552.2 (M+H)+

172

2-((S)-2-(3-(3,5-Bis(trifluoromethyl)phenyl)ureido)-3-methylbutanamido)-3- (1-methyl-1H-imidazol-4-yl)propanoic acid (166e)

1 H NMR (500 MHz, CDCl3) δ 0.73- 0.76 (m, 6H), 2.03- 2.05 (m, 1H), 2.73- 3.22 (m, 2H), 3.45- 3.69 (m, 3H), 4.10- 4.35 (m, 3H), 6.91 (s, 1H), 7.22- 7.44(m, 1H), 13 7.51- 7.77 (d, 3H), 10.40 (s, 1H). C NMR (125Hz, CDCl3) δ 18.1, 19.2,29.1, 31.6, 33.3, 52.2, 53.3, 59.1, 114.9, 118.0, 118.1, 122.2, 124.4, 126.5, 131.3, 131.8, 137.0, 137.6, 141.2, 155.2, 171.4, 173.7. MS(ESI) 522.0 (M-H)-

2-((S)-2-(3-(3,5-Bis(trifluoromethyl)phenyl)ureido)propanamido)-3-(1-methyl- 1H-imidazol-4-yl)propanoic acid (166f)

1 H NMR (500 MHz, CDCl3) δ 1.26(d, J = 7Hz, 6H), 2.88- 3.07 (m, 2H), 3.55 (s, 3H), 3.75- 3.80 (m, 1H), 4.24- 4.27 (t, 1H), 4.49- 4.50 (m, 1H), 6.81 (d, J= 7Hz 1H), 7.17 (s, 1H), 7.56 (s, 1H) 8.05 (s, 2H), 8.20 (s, 1H), 8.45 (d, J= 8Hz, 1H), 9.76 (s, 1H). MS(ESI) 495.4 (M+H)+

173

Methyl2-((S)-2-(3-(3,5-bis(trifluoromethyl)phenyl)ureido)-3- phenylpropanamido)-3-(1-methyl-1H-imidazol-4-yl)propanoate (166g)

1 H NMR (500 MHz, CDCl3) δ 2.92- 2.99 (m, 1H), 3.06- 3.14 (m, 3H), 3.56 (s, 3H), 3.66 (s, 3H), 4.69- 4.74 m, 2H), 6.59- 6.69 (m, 2H), 7.13- 7.26 (m, 7H), 7.34 13 (s, 1H), 7.82 (s, 2H), 8.00(s, 1H), 8.48 (s, 1H). C NMR (125Hz, CDCl3) δ 29.1, 33.3, 38.7, 52.4, 53.0, 55.2, 115.0, 117.9, 118.3, 126.9, 128.4, 128.5, 129.3, 129.5, 131.6, 131.9, 137.5, 141.1, 154.8, 171.3, 173.1. MS(ESI) 586.2 (M+H)+

(R)-Methyl 2-((S)-2-(3-(3,5-bis(trifluoromethyl)phenyl)ureido)-3-(1H-indol-3- yl)propanamido)-3-(1-methyl-1H-imidazol-4-yl)propanoate (166h)

1 H NMR (500 MHz, CDCl3) δ 2.85- 2.99(m, 2H), 3.00- 3.03 (m, 1H), 3.17- 3.22 (m, 1H), 3.53 (s, 3H),3.63 (s, 3H), 4.53- 4.57 (m, 2H), 6.49- 6.50 (m, 1H), 6.85 (s, 1H), 6.94- 6.97 (m, 1H), 7.04- 7.07 (m, 1H),7.14 (s, 1H), 7.32- 7.42 (m, 1H), 7.55- 7.60 (m, 2H), 7.98 (s, 2H), 8.64 (s, 1H), 9.41 (s, 1H), 10.87 (s, 1H). 13C NMR

(125Hz, CDCl3) ) δ 28.6, 30.4, 32.1, 33.1, 52.6, 52.9, 53.8, 109.8, 117.5, 118.2,

174

118.4, 118.9, 119.0, 122.7, 124.9, 127.1,128.0, 131.1, 131.3, 136.6, 137.3, 142.8, 154.7, 172.2, 172.5. MS(ESI) 625.2 (M+H)+

(3S)-Benzyl 3-(3-(3,5-bis(trifluoromethyl)phenyl)ureido)-4-((1-methoxy-3-(1- methyl-1H-imidazol-4-yl)-1-oxopropan-2-yl)amino)-4-oxobutanoate (166i)

1 H NMR (500 MHz, CDCl3) δ 2.87- 2.92(m, 1H), 3.02- 3.07 (m, 3H), 3.49 (s, 3H), 3.57 (s, 3H), 4.72- 4.76 (m, 1H), 4.87- 4.90 (m, 1H), 5.02- 5.08 (q, 2H), 6.66 (s, 1H), 6.80(d, J= 8.5Hz, 1H), 7.24 (s, 6H), 7.35 (s, 1H), 7.82 (s, 2H), 8.06 (d, J= 13 7.5Hz, 1H), 9.00 (s, 1H). C NMR (125Hz, CDCl3) δ 29.2, 33.4, 36.6, 50.0, 52.4, 52.7, 66.8, 115.1, 118.0, 118.4, 122.2, 124.4, 128.1, 128.5, 135.4, 136.6, 137.5, 141.3, 154.7, 171.3, 173.4, 171.9. MS(ESI) 644.3 (M+H)+

175

(4S)-Benzyl 4-(3-(3,5-bis(trifluoromethyl)phenyl)ureido)-5-((1-methoxy-3-(1- methyl-1H-imidazol-4-yl)-1-oxopropan-2-yl)amino)-5-oxopentanoate (166j)

1 H NMR (500 MHz, CDCl3) δ 1.97- 2.02(m, 2H), 2.17- 2.18 (m, 1H), 2.51- 2.54 (m, 2H), 3.08- 3.09 (m, 2H), 3.53 (s, 3H), 3.61 (s, 3H), 4.52- 4.54 (m, 1H), 4.50- 4.75 (m, 1H), 5.07 (s, 2H), 6.71(s, 2H), 7.24- 7.37 (m, 7H), 7.81(s, 2H), 8.13- 8.14 13 (m, 1H), 8.55 (m, 1H). C NMR (125Hz, CDCl3) δ 28.0, 28.8, 30.3, 33.6, 52.5, 52.8, 53.1, 66.5, 118.0, 118.6, 122.2, 124.4, 128.1, 128.2, 128.5, 131.6, 131.9, 135.8, 136.0, 137.3, 141.2, 154.9, 171.2, 173.0, 173.2. MS(ESI) 658.3 (M+H)+

Methyl 2 -((S)-2-(3-(3,5-bis(trifluoromethyl)phenyl)ureido)-3- methylbutanamido)-3-(1-ethyl-1H-imidazol-4-yl)propanoate (166k)

1 H NMR (500 MHz, CDCl3) δ 0.94- 1.1.03 (m, 6H),1.35- 1.38 (t, 3H), 2.07- 2.11 (m, 1H), 3.06- 3.08 (m, 2H), 3.62 (s, 3H), 3.84- 3.89 (q, 2H), 4.35- 4.38 (m, 1H), 4.68- 4.70 (m, 1H), 6.73- 6.78 (m, 2H), 7.31 (s, 1H), 7.37 (s, 1H), 7.79 (s, 2H), 13 8.37- 8.39 (m,1H), 8.50 (s, 1H). C NMR (125Hz, CDCl3) δ 16.0, 18.1, 19.3, 29.0, 31.7, 41.9, 52.2, 53.3, 59.3, 116.4, 118.0, 122.2, 124.4, 131.3, 131.6, 131.8, 132.1, 136.4, 136.9, 141.3, 155.2, 171.3, 173.7. MS(ESI) 552.2 (M+H)+

176

Methyl 2-((S)-2-(3-(3,5-bis(trifluoromethyl)phenyl)ureido)-3,3- dimethylbutanamido)-3-(1-methyl-1H-imidazol-4-yl)propanoate (166l)

1 H NMR (500 MHz, CDCl3) δ 1.07 (s, 9H), 2.99- 3.09 (m, 2H), 3.58 (s, 3H), 3.66 (s, 3H), 4.35- 4.37(m, 1H), 4.62- 4.65 (m, 1H), 6.66 (s, 1H), 6.72-6.74 (m, 1H), 13 7.24-7.35 (m, 2H), 7.81(s, 1H), 8.28- 8.44 (m, 2H). C NMR (125Hz, CDCl3) δ, 26.7, 33.3, 33.7, 36.6, 52.2, 53.1, 61.6, 116.5, 118.4, 122.4, 124.4, 131.3, 131.8, 136.1, 136.7, 141.6, 155.3, 171.3, 172.2. MS(ESI) 552.2 (M+H)+

Methyl3-(1-methyl-1H-imidazol-4-yl)-2-((S)-3-methyl-2-(3-(3- (trifluoromethyl)phenyl)ureido)butanamido)propanoate (166m)

1 H NMR (500 MHz, CDCl3) δ 0.98- 1.05 (m, 6H),2.10- 2.14 (m, 1H), 3.07- 3.08 (m, 2H), 3.53 (s, 3H), 3.66(s, 3H), 4.39- 4.42 (m, 1H), 4.75- 4.79 (m, 1H), 6.69(m, 1H), 6.78- 6.80 (m, 1H), 7.12- 7.14 (m, 1H), 7.20- 7.23(m, 1H), 7.29 (s, 1H), 7.34- 7.36 (m, 1H), 7.73(s, 1H), 8.27- 8.29 (m, 1H), 8.34 (s, 1H). 13C NMR (125Hz,

CDCl3) δ 18.1, 19.2, 29.2, 31.7, 33.2, 52.2, 53.0, 59.1, 115.4, 118.1, 118.5, 121.8

177

123.0, 129.1, 130.7, 131.0, 137.0, 137.6, 140.2, 155.6, 171.5, 173.5. MS(ESI) 470.2 (M+H)+

Methyl2-((S)-2-(3-(3,5-bis(trifluoromethyl)phenyl)ureido)-3- methylbutanamido)-3-(1H-imidazol-4-yl)propanoate (166n)

1 H NMR (500 MHz, CDCl3) δ 0.81- 0.89 (m, 6H), 1.97- 2.02 (m, 1H), 2.86-2.94 (m, 2H), 3.57 (s, 3H), 4.17- 4.20 (m, 1H), 4.48- 4.53(m, 1H), 6.54(d, J= 8.5Hz, 1H), 6.81 (s, 1H), 7.50 (s, 1H), 7.56(s, 1H), 7.99(s, 2H), 8.52 (d, J = 7Hz, 1H), 13 9.42(s, 1H), 11.80 (s, 1H). C NMR (125Hz, CDCl3) δ 17.5, 19.0,36.5, 336.6, 52.2, 52.4, 59.1, 114.4, 117.7, 117.9, 122.2, 124.3, 131.5, 131.8, 134.4, 141.5, 155.4, 170.9, 172.3. MS(ESI) 524.2 (M+H)+

Methyl 2-((S)-2-(3-(3,5-bis(trifluoromethyl)phenyl)ureido)-3,3- dimethylbutanamido)-3-(1-ethyl-1H-imidazol-4-yl)propanoate (166o)

1 H NMR (500 MHz, CDCl3) δ 1.05 (s, 9H), 1.35- 1.38 (m, 2H), 2.63- 2.65 (t, 2H), 3.64 (s, 3H), 3.88- 3.91 (q, 4H), 4.24- 4.26(m, 1H), 4.64- 4.68 (m, 1H), 6.78- 6.82 (m, 2H), 7.36 (s, 1H), 7.61(s, 1H), 7.87 (s, 1H), 8.03- 8.05 (m, 1H), 8.85 (s, 1H). 178

13 C NMR (125Hz, CDCl3) δ 15.9, 26.8, 34.8, 36.7, 42.0, 52.2, 53.2, 61.7, 116.5, 118.4, 122.4, 124.4, 131.3, 131.8, 136.1, 136.7, 141.6, 155.3, 171.3, 172.2. MS(ESI) 566.3 (M+H)+

(R)-Methyl 6-(((benzyloxy)carbonyl)amino)-2-((R)-2-(3-(3,5- bis(trifluoromethyl)phenyl)ureido)-3-methylbutanamido)hexanoate (167)

1 H NMR (500 MHz, CDCl3) δ 1.01- 1.10 (m, 6H), 1.33- 1.48 (m, 4H), 1.72- 1.77 (m, 2H), 2.05- 2.11 (m, 1H), 3.05- 3.08 (m, 1H), 3.21- 3.23 (m, 1H), 3.66 (s, 3H), 4.35- 4.54 (m, 2H), 5.14- 5.15 (m, 2H), 6.84- 6.86 (m, 1H), 7.30- 7.36 (m, 6H), 13 7.54(m, 1H), 7.77 (s, 2H), 7.85 (m, 1H), 8.28 (s, 1H). C NMR (125Hz, CDCl3) δ 18.2, 19.3, 22.3, 29.6, 30.4, 31.9, 39.8, 52.2, 53.3, 58.8, 67.0, 115.3, 118.1, 122.1, 124.3, 127.5, 128.2, 128.3, 128.6, 131.8, 132.0, 136.3, 140.9, 155.4, 157.3, 172.0, 174.1. MS(ESI) 649.3 (M+H)+

179

Methyl 2-((S)-2-(3-(3,5-bis(trifluoromethyl)phenyl)thioureido)-3- methylbutanamido)-3-(1-methyl-1H-imidazol-4-yl)propanoate (168)

1 H NMR (500 MHz, CDCl3) δ 1.01- 1.05 (m, 6H), 2.13- 2.25 (m, 1H), 3.07- 3.08 (m, 2H), 3.57 (s, 3H), 3.65(s, 3H), 4.63- 4.66 (m, 1H), 4.88- 4.90(m, 1H), 6.72(s 461H), 7.50 (s, 2H), 8.08 (s, 1H), 8.20(s, 1H), 9.46 (s, 1H). 13C NMR (125Hz,

CDCl3) δ 18.2, 19.1, 29.0, 31.4, 31.8, 53.2, 53.3, 59.1, 107.9, 118.0, 122.2, 124.4, 131.8, 134.0, 141.2, 155.2, 171.3, 173.7. MS(ESI) 553.5 (M+H)+

180

1. Hirano, T.; Ishihara, K.; Hibi, N. Roles of STAT3 in Mediating the Cell Growth, Differentiation and Survival Signals Relayed Through the IL-6 Family of Cytokine Receptors. Oncogene 2000, 19, 2548. 2. Bromberg, J.; Darnell, J. E., Jr. The role of STATs in Transcriptional Control and their Impact on Cellular Function. Oncogene 2000, 19, 2468. 3. Darnell, J. E., Jr. STATs and Gene Regulation. Science 1997, 277, 1630. 4. Darnell, J. E.; Kerr, I.M.; Stark, G.R. Jak-STAT Pathways and Transcriptional Activation in Response to IFNs and Other Extracellular Signaling Proteins. Science 1994, 264, 1415. 5. Darnell, J.E. STATs and Gene Regulation. Science 1997, 277, 1630. 6. Turkson, J.; Jove, R. STAT Proteins: Novel Molecular Targets for Cancer Drug Discovery. Oncogene 2000, 19, 6613. 7. Levy, D.E.; Darnell, J.E. Stats: Transcriptional Control and Biological Impact. Nat. Rev. Mol. Cell Biol. 2002, 3, 651. 8. Yu, H.; Jove, R. The STATs of Cancer; New Molecular Targets Come of Age. Nat. Rev. Cancer 2004, 4, 97. 9. Darnell, J. E., Jr. Transcription Factors as Targets for Cancer Therapy. Nat. Rev. Cancer. 2002, 2, 740. 10. Redell, M.S.; Tweardy, D.J. Targeting Transcription Factors for Cancer Therapy. Curr. Pharm. Des. 2005, 11, 2873. 11. Catlett-Falcone R.; Landowski T.H.; Oshiro M.M.; Turkson J.; Levitzki A.; Savino R.; Ciliberto, G.; Moscinski, L.; Fernandez-Luna, J.L.; Nunez, G.; Dalton, W.S.; Jove R. Constitutive Activation of STAT3 Signaling Confers Resistance to Apoptosis in HumanU266 Myeloma Cells. Immunity 1999, 10, 105 12. Ling, X.; Arlinghaus, R.B. Knockdown of STAT3 Expression by RNA Interference Inhibits the Induction of Breast Tumors in Immune Competent Mice. Cancer Res. 2005, 65, 2532. 13. Gao, L.; Zhang, L.; Hu, J.; Li, F.; Shao, Y.; Zhao, D.; Kalvakolanu, D.V.; Kopecko, D.J.; Zhao, X.; Xu, D.Q. Down-Regulation of Signal Transducer and Activator of Transcription 3Expression using Vector-based Small Interfering RNAs Suppresses Growth of Human Prostate Tumor in vivo. Clin. Cancer Res. 2005, 11, 6333.

181

14. Barton, B.E.; Murphy, T.F.; Shu, P.; Huang, H.F.; Meyenhofer, M.; Barton, A. Novel Single Stranded Oligonucleotides that Inhibit Signal Transducer and Activator of Transcription 3 Induce Apoptosis in vitro and in vivo in Prostate Cancer Cell lines. Mol. Cancer Ther. 2004, 3, 1183. 15. Leong, P.L.; Andrews, G.A.; Johnson, D.E.; Dyer, K.F.; Xi, S.; Mai, J.C.; Robbins, P.D.; Gadiparthi, S.; Burke, N.A.; Watkins, S.F.; Grandis, J.R. Targeted Inhibition of STAT3 with a Decoy Oligonucleotide Abrogates Head and Neck Cancer Cell Growth. Proc. Natl. Acad. Sci. USA. 2003, 100, 4138. 16. Pedranzini, L.; Dechow, T.; Berishaj, M.; Comenzo, R.; Zhou, P.; Azare, J.; Bornmann, W.; Bromberg, J. Pyridone 6, a Pan-Janus Activated Kinase Inhibitor, Induces Growth Inhibition of Multiple Myeloma Cells. Cancer Res. 2006, 66, 9714. 17. Kotha, A.; Sekharam, M.; Cilenti, L.; Siddiquee, K.; Khaled, A.; Zervos, A.S.; Carter, B.; Turkson, J.; Jove, R. Resveratrol Inhibits Src and STAT3 Signaling and Induces the Apoptosis of Malignant Cells Containing Activated STAT3 Protein. Mol. Cancer Ther. 2006, 5, 621. 18. Blaskovich, M.A.; Sun, J.; Cantor, A.; Turkson, J.; Jove, R.; Sebti, S.M. Discovery of JSI-124 (Cucurbitacin I), a Selective Janus Kinase/ Signal Transducer and Activator of Transcription 3 Signaling Pathway Inhibitor with Potent Antitumor Activity Against Human and Murine Cancer Cells in Mice. Cancer Res. 2003, 63, 1270. 19. Sun, J.; Blaskovich, M.A.; Jove, R.; Livingston, S.K.; Coppola, D.; Sebti, S.M.; Cucurbitacin, Q. A selective STAT3 Activation Inhibitor with Potent Antitumor Activity. Oncogene 2005, 24, 3236. 20. Shimizu, M.; Weinstein, I.B. Modulation of Signal Transduction by Tea Catechins and Related Phytochemicals. Mutat. Res. 2005, 591, 147. 21. Ren, Z.; Cabell, L. A.; Schaefer, T. S.; McMurray, J. S. Identification of a High-Affinity Phosphopeptide Inhibitor of STAT3. Bioorg. Med. Chem. Lett. 2003, 13, 633. 22. Chen, J.; Nikolovska-Coleska, Z.; Yang, C.-Y.; Gomez, C.; Gao, W.; Krajewski, K.; Jiang, S.; Roller, P.; Wang, S. Design and synthesis of a new, Conformationally Constrained, Macrocyclic Small-Molecule Inhibitor of STAT3 via ‘Click Chemistry’. Bioorg. Med. Chem. Lett. 2007, 17, 3939.

182

23. Coleman, D. R., IV; Ren, Z.; Mandal, P. K.; Cameron, A. G.; Dyer, G. A.; Muranjan, S.; Campbell, M.; Chen, X.; McMurray, J. S. Investigation of the Binding Determinants of Phosphopeptides Targeted to the Src Homology 2 Domain of the Signal Transducer and Activator of Transcription 3. Development of a High-Affinity Peptide Inhibitor J. Med. Chem. 2005, 48, 6661 24. Siddiquee, K. A.; Gunning, P. T.; Glenn, M.; Katt, W. P.; Zhang, S.; Schroeck, C.; Sebti, S. M.; Jove, R.; Hamilton, A. D.; Turkson. An Oxazole-Based Small- Molecule Stat3 Inhibitor Modulates Stat3 Stability and Processing and Induces Antitumor Cell Effects. J. ACS Chem. Biol. 2007, 2, 787 25. Zhang, X.; Yue, P.; Fletcher, S.; Zhao, W.; Gunning, P. T.; Turkson, J. A Novel Small-Molecule Disrupts STAT3 SH2 Domain Phosphotyrosine Interaction and STAT3-Dependent Tumor Process. Biochem. Pharmacol. 2010, 79, 1398. 26. Mandal, P. K.; Liao, W. S.-L.; McMurray, J. S. Synthesis of Phosphatase- Stable Cell-Permeable Peptidomimetic Prodrugs that Target the SH2 Domain of STAT3. Org. Lett. 2009, 11, 3394. 27. Chen, J.; Bai, L.; Bernard, D.; Nikolovska-Coleska, Z.; Gomez, C.; Zhang, J.; Yi, H.; Wang, S. Structure-Based Design of Conformationally Constrained Cell- Permeable STAT3 Inhibitors. ASC. Med. Chem Lett. 2010, 1, 85. 28. Gomez, C.; Bai, L.; Zhang, J.; Nikolovska-Coleska, Z.; Chen, J.; Yi, H.; Wang, S. Design, Synthesis, and Evaluation of Peptidomimetics Containing Freidinger Lactams as STAT3 Inhibitors. Bioorg. Med. Chem. Lett. 2009, 19, 1733. 29. Ren,X.; Duan,L.; He, Q.; Zhang, Z.; Zhou,Y.; Wu, D.; Pan, J.; Pei, D.; Ding, K Identification of Niclosamide as a New Small-Molecule Inhibitor of the STAT3 Signaling Pathway. ACS. Med. Chem. Lett. 2010, 1, 454. 30. Yu,Z –Y.; Huang, R.; Xiao, H.; Sun, W –F.; Shan, Y –J.; Wang, B.; Zhao, T – T.; Dong, B.; Zhao, Z –H.; Liu,X –L.; Wang, S –Q.; Yang, R –F.; Luo, Q –L.; Cong, Y –W. Fluacrypyrim, a Novel STAT3 Activation Inhibitor, Induces Cell Cycle Arrest and Apoptosis in Cancer Cells Harboring Constitutively-Active STAT3. Int. J. Cancer 2010, 127, 1259. 31 Liu, Y.; Liu, A.; Xu, Z.; Yu; Wang, H.; Li, C.; Lin, J. XZH-5 Inhibits STAT3 Phosphorylation and causes Apoptosis in Human Hepatocellular Carcinoma Cells Apoptosis 2011, 16, 502. 32. Cohen, L.A; Jain, R.; Regiospecific alkylation of histidine and histamine at N-1 (τ). Tetrahedron 1996, 52, 5363 183

SPECTRA

SECTION 1.8.1 and 1.8.2

184

185

186

187

188

189

190

191

192

193

SECTION 1.8.3

194

195

Copy of O041409F_090414115914 #1-10 RT: 0.01-0.22 AV: 10 NL: 5.24E8 T: FTMS + p ESI Full ms [100.00-1000.00] 313.1653 100 95 90 85 80 75 70 65 60 55 50 45

40 RelativeAbundance 35 30 321.1318 25 20 308.2082 15 335.1474 10 293.1971 5 214.0974 261.0208 243.0480 345.1918 378.9405 395.1558 429.1062 456.2598 496.2909 0 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500 m/z

196

197

198

Copy (3) of O041409A #1-10 RT: 0.01-0.22 AV: 10 NL: 9.54E7 T: FTMS + p ESI Full ms [100.00-1000.00] 251.1500 100 95 90 85 80 75 257.1583 70 65 60 55 50 45

40 RelativeAbundance 35 273.1320 30 25

20 152.0816 15 365.2585 10 371.3155 236.1393 359.2401 5 104.9919 390.2497 219.0176 134.0710 171.1378 195.0876 291.1814 313.1434 335.1253 0 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 m/z

199

200

201

Copy (2) of O041409G_090414115914 #1-10 RT: 0.01-0.22 AV: 10 NL: 1.61E7 T: FTMS + p ESI Full ms [100.00-1000.00] 293.1976 100 95 90 85 80 75 70 65 60 55 50 45

40 RelativeAbundance 35 30 25 289.0440 20 294.2008 15 10 291.0450 299.1507 5 292.9101 295.0416 297.0119 290.0477 292.0148 293.7416 296.0591 298.0150 0 288 289 290 291 292 293 294 295 296 297 298 299 300 m/z

202

203

Copy (2) of O041409D_090414115914 #1-10 RT: 0.00-0.22 AV: 10 NL: 3.15E8 T: FTMS + p ESI Full ms [100.00-1000.00] 299.1500 100 95 90 85 80 75 70 65 60 305.1582 55 50 45

40 RelativeAbundance 35 30 321.1320 25 20 15 10 331.2297 5 293.1974 353.9857 404.2079 225.1961 257.1398 378.9408 426.1897 446.2184 472.1036 494.0851 0 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500 m/z

204

205

Copy (2) of O041409E_090414115914 #1-10 RT: 0.00-0.22 AV: 10 NL: 4.01E7 T: FTMS + p ESI Full ms [100.00-1000.00] 456.2604 100 95 90 85 80 75 70 65 60 55 50 45

40 RelativeAbundance 35 30 396.2395 459.2701 25 20 15 356.2083 400.1981 10 388.9559 468.2604 449.2047 350.9461 478.2423 5 311.1504 321.1923 378.9410 440.2293 341.1861 358.9802 412.1980 422.2187 0 300 320 340 360 380 400 420 440 460 480 m/z

206

207

208

Copy (2) of O041409C #1 RT: 0.01 AV: 1 NL: 3.23E8 T: FTMS + p ESI Full ms [100.00-1000.00] 404.2079 100 95 90 85 80 75 70 65 60 55 50 45

40 RelativeAbundance 35 293.1973 30 299.1504 410.2172 25 20 257.1397 15 315.1793 426.1900 10 251.1010 267.0786 5 283.0510 220.1081 240.1132 335.1530 359.1869 387.1818 451.1980 486.1986 0 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500 m/z

209

SECTION 1.8.4

210

211

212

213

214

215

216

217

218

219

220

221

222

223

224

225

226

227

228

SECTION 1.8.5

H-H Cosy :

229

NOESY of 144a

NOE

230

NOESY of 145a

NOE

231

232

233

234

235

236

237

238

239

240

241

242

243

244

245

246

247

248

249

250

251

252

253

254

255

256

257

258

259

260

261

262

263

264

265

266

267

268

269

270

1H NMR of the Mixture of the reaction with Copper catalyst

271

1H NMR of the Mixture of the reaction without Copper catalyst

272

SCETION 1.8.6

273

274

275

276

277

278

279

280

281

282

283

284

285

286

287

288

PARTI: SECTION 2.1

289

290

291

292

293

294

295

296

297

298

299

300

301

302

303

304

305

306

307

308

309

310

311

312

313

314

315

316

317

318

319

320

321

322

323

324

325

326

327

328

329

330

331

332

333

334

335