Studies Toward the Diastereoselective Semisynthesis of Taxol Joshua William Lee

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FLORIDA STATE UNIVERSITY

COLLEGE OF ARTS AND SCIENCES

STUDIES TOWARD THE DIASTEREOSELECTIVE SEMISYNTHESIS OF TAXOL

Joshua William Lee

A Thesis submitted to the Department of Chemistry and Biochemistry in partial fulfillment of the requirements for the degree of Master of Science

Degree Awarded Summer Semester, 2008

The members of the committee approve the thesis of Joshua W. Lee on April 24, 2008.

Robert A. Holton Professor Directing Thesis

Marie E. Krafft Committee Member

Gregory B. Dudley Committee Member

Kenneth A. Goldsby Committee Member

The Office of Graduate Studies has verified and approved the above named committee members.

TABLE OF CONTENTS

LIST OF FIGURES ...... v LIST OF TABLES ...... vi LIST OF SCHEMES ...... vii LIST OF ABREVIATIONS...... viii ABSTRACT...... x CHAPTER I. INTRODUCTION ...... 1 History...... 1 Synthesis...... 2 I. Biosynthesis ...... 2 II. Total synthesis ...... 2 III. Semisynthesis...... 3 Esterification of 7-TES-Baccatin III ...... 3 Methods for Synthesis of the C-13 Side Chain ...... 5 A) β-Phenylglycidates ...... 5 B) 4-Phenyl-1-Butene Derivatives ...... 6 C) Ketene Acetals...... 7 D) Glycolyl Sultam Enolates...... 8 E) Thioester enolates...... 8 F) Asymmetric Oxaziridine-Mediated Hydroxylation ...... 9 G) Β-Lactams ...... 10 CHAPTER II. RESULTS and DISCUSSION...... 14 I. Solvent effects on diastereoselectivity...... 16 A) Ethereal and Non-Aromatic Solvents...... 16 B) Aromatic Solvents ...... 17 II. Counterion...... 19 A) Lithium...... 19 B) Sodium...... 20 C) Potassium...... 21 D) Magnesium...... 22 E) Lanthanide Alkoxides...... 26 F) Alkyl – Lanthanide Alkoxides...... 28 iii

G) Ammonium ...... 30 III. Coordinating Ligands...... 31 IV. Conclusion ...... 33 Chapter III: Experimental...... 34 Preparation of β-Lactam 32...... 35 Preparation of 7-TES-Baccatin III ...... 37 Coupling Reaction...... 38 I. General Procedure...... 38 II. Procedure for Transmetallation...... 38 Appendix...... 39 BIOGRAPHICAL SKETCH ...... 56

LIST OF FIGURES

FIGURE 1. STRUCTURE OF TAXOL AND 10-DAB...... 1 FIGURE 2. STERIC ENVIRONMENT OF C-13 HYDROXYL...... 3 FIGURE 3. N-ACYL-Β-LACTAM...... 11 FIGURE 4. DIASTEREOSELECTIVITY OF C-13 LITHIUM ALKOXIDE WITH RACEMIC Β-LACTAM ...... 15 FIGURE 5. T-BOC PROTECTED Β-LACTAM...... 18 FIGURE 6. DIASTEREOSELECTIVITY OF C-13 HALO-MAGNESIUM ALKOXIDE WITH RACEMIC Β-LACTAM23 FIGURE 7. DIASTEREOSELECTIVITY OF C-13 ALKYLMAGNESIUM ALKOXIDE WITH RACEMIC Β-LACTAM

32 25 FIGURE 8. MAGNESIUM BIS-AMIDES ...... 26 FIGURE 9. D.E. VS REACTION CONVERSION ...... 28 FIGURE 10. BASES USED FOR LIGAND COORDINATION ...... 31

LIST OF TABLES

TABLE 1. DIASTEREOSELECTIVITY IN ETHEREAL AND NON-AROMATIC SOLVENTS...... 17 TABLE 2. EFFECT OF AROMATIC SOLVENTS ON THE DIASTEREOSELECTIVITY...... 18 TABLE 3. SELECTIVITY OF LITHIUM ALKOXIDES...... 19 TABLE 4. SELECTIVITY OF LITHIUM ALKOXIDE WITH AN EXCESS OF LITHIUM ...... 20 TABLE 5. SELECTIVITY OF HALO-MAGNESIUM ALKOXIDES...... 22 TABLE 6. SELECTIVITY OF ALKYLMAGNESIUM ALKOXIDES...... 24 TABLE 7. SELECTIVITY OF AMIDE-MAGNESIUM ALKOXIDE...... 26 TABLE 8. SELECTIVITY OF LANTHANIDE ALKOXIDES...... 27 TABLE 9. ALKYL -LANTHANIDE ALKOXIDES...... 29 TABLE 10. SELECTIVITY OF AMMONIUM ALKOXIDES ...... 30 TABLE 11. SELECTIVITY OF COORDINATION LIGANDS ...... 32

LIST OF SCHEMES

SCHEME 1. BIOSYNTHESIS...... 2 SCHEME 2. SYNTHESIS OF 7-TES-BACCATIN III ...... 3 SCHEME 3. THE FIRST SEMISYNTHESIS OF TAXOL ...... 4 5 SCHEME 4. GREEN-POTIER ESTERIFICATION ...... 5 SCHEME 5. SYNTHESIS OF TAXOL SIDE CHAIN FROM CIS-Β-PHENYLGLYCIDATES ...... 5 SCHEME 6. SYNTHESIS OF TAXOL SIDE CHAIN FROM TRANS-Β-PHENYL METHYL GLYCIDATE ...... 6 SCHEME 7. SYNTHESIS OF TAXOL SIDE CHAIN FROM 4-PHENYL-1-BUTENE DERIVATIVES ...... 7 SCHEME 8. SYNTHESIS OF TAXOL SIDE CHAIN FROM KETENE ACETALS ...... 7 SCHEME 9. SYNTHESIS OF TAXOL SIDE CHAIN FROM GLYCOLYL SULTAM ENOLATES...... 8 SCHEME 10. SYNTHESIS OF TAXOL SIDE CHAIN FROM THIOESTER ENOLATES ...... 9 SCHEME 11. SYNTHESIS OF TAXOL SIDE CHAIN VIA ASYMMETRIC HYDROXYLATION ...... 10 SCHEME 12. FORMATION OF Β-LACTAM BY THE STAUDINGER REACTION...... 11 SCHEME 13. FORMATION OF Β-LACTAM BY AN ESTER ENOLATE-IMINE CYCLOADDITION ...... 11 SCHEME 14. ESTERIFICATION OF 7-TES-BACCATIN III WITH N-ACYL-Β-LACTAMS ...... 12 SCHEME 15. ESTERFICATION OF 7-TES-BACCATIN III LITHIUM ALKOXIDE WITH Β-LACTAM ...... 12 SCHEME 16. DIASTEREOSELECTIVITY OF COUPLING REACTION...... 12 SCHEME 17. DIASTEREOSELECTIVE SEMISYNTHESIS OF TAXOL ...... 13 SCHEME 18. SYNTHESIS OF Β-LACTAM 32 ...... 14 SCHEME 19. SYNTHESIS OF 7-TES-BACCATIN III...... 15 SCHEME 20. SODIUM ALKOXIDE...... 21 SCHEME 21. POTASSIUM ALKOXIDE ...... 21 43 SCHEME 22. FORMATION OF DIALKYL MAGNESIUM FROM ALKYLMAGNESIUM IODIDES ...... 23 SCHEME 23. SYNTHESIS OF MAGNESIUM BIS-AMIDES ...... 25 SCHEME 24. SYNTHESIS OF ALKYL LANTHANIDES ...... 29 SCHEME 25. SYNTHESIS OF COORDINATING BASES...... 31

vii

LIST OF ABREVIATIONS

Ac acetyl Bn benzyl Bu butyl Bz benzoyl °C degrees centigrade CAN ceric ammonium nitrate DCC 1,3-dicyclohexylcarbodiimide DCM dichloromethane, methylene chloride D.E. diastereomeric excess DMAP 4-dimethylaminopyridine DME ethylene glycol dimethyl ether DMF N,N-dimethylformamide DMM dimethoxymethane DPC di-2-pyridyl carbonate eq equivalent(s) Et ethyl g gram(s) HMPA hexamethylphosphoramide KHMDS potassium hexamethyldisilazide LDA lithium di-iso-propylamide LHMDS lithium hexamethyldisilazide Me methyl mg milligram(s) min minutes mL milliliter(s) mol mole(s) MOP methoxy propyl viii

NaHMDS sodium hexamethyldisilazide Ph phenyl PMP para-methoxyphenyl Pr propyl PTSA para-toluenesulfonic acid rt room temperature TES triethylsilyl THF tetrahydrofuran TMTHF 2,2,5,5-tetramethyltetrahydrofuran

ABSTRACT

Substantial attention has been given to the synthesis of Taxol due to its cytotoxic activity towards certain cancers. Because of Taxol’s structural complexity, total synthesis of the molecule cannot provide a commercial supply. Its semisynthesis from the more abundant 10-DAB solved the supply problem and allowed the drug to be produced in mass quantities. The key step in the semisynthesis is the attachment of a chiral side chain at C-13 by acylation through the use of a β-lactam. The coupling reaction with a racemic N-benzoyl β-lactam proved to be diastereoselective giving a 3:1 ratio in favor of Taxol, which means it is possible to attach the chiral side chain by kinetic resolution of the racemic material. However, the separation of Taxol from its epimer proved to be difficult and time consuming We envisaged that the selectivity could be improved to favor Taxol exclusively. An investigation has been launched to test the potential of this selectivity towards Taxol through the use of aromatic, ethereal and non-aromatic solvents, counter ions and coordination ligands. This study has revealed that the selectivity can be improved by the use of fluorinated aromatic solvents. Secondly, the counter ion on the C-13 alkoxide has a significant effect on the selectivity. Also, the use of alkoxyamines as coordination ligands increases this selectivity in-favor of Taxol. Finally, this work has resulted in the improvement in the selectivity to 8:1 in favor of Taxol by the use of fluorinated aromatic solvents, cerium alkoxides, and alkoxyamines as coordination ligands.

CHAPTER I. INTRODUCTION

History

Since its isolation in 1971 by Wani and Wall,1 Taxol 1 (isolated in nature from the Pacific yew Taxus brevifolia) has garnered much attention in the realm of synthesis. This recognition is due to not only its structural complexity, but also its cytotoxic activity towards metastatic ovarian and breast cancers. The development of Taxol was hindered throughout much of the 1970’s because of three major problems.2 First, although it showed broad activity, when it was compared to the activity of other antitumor agents in development at that time, Taxol was considered not to have remarkable antitumor activity. Secondly, a major obstacle was the lack of a reasonable synthetic route, which made large scale acquirement of the drug nearly impossible due to its scarcity in nature (0.014% from the bark of T. brevifolia).3 The last major problem in its advancement came from its low solubility in water, which made it difficult to formulate.

Figure 1. Structure of Taxol and 10-DAB

The concernment in Taxol was renewed in 1979 when Horwitz et al. discovered the drugs rare mechanism of action, which is responsible for its antimiotic activity.4 They showed that Taxol promotes the polymerization of tubulin, which are cellular proteins that aid in mitosis. This polymerization causes stable microtubules to assemble, thus inhibiting cell mitosis. On the other hand, the problem of low solubility was overcome initially by formulating it as an emulsion with Cremophor EL, a polyethoxylated castor

oil, and later by the use of prodrugs.3 In addition to that, the inherent supply problem was overcome by the semisynthesis of Taxol from the more abundant taxane 10-deacetyl baccatin III (10-DAB) 2. Not only could 10-DAB be isolated in a much higher yield than that of Taxol from the T. brevifolia bark, but it could also be extracted from the leaves of the English yew (Taxus Baccata), a renewable source of the Taxol precursor.5

Synthesis

I. Biosynthesis6

Taxol’s proposed biosynthesis consists of a series of cyclizations from geranylgeranyl pyrophosphate 3 to give the taxane skeleton 4 (Scheme 1). A series of oxidations follow to give Baccatin III 5. Then addition of phenylisoserine (from β - phenylalanine) to C-13 completes the synthesis.

Scheme 1. Biosynthesis

II. Total synthesis

Due to the structural complexity of Taxol, its total synthesis has been vehemently pursued by several groups. To date there have been seven total syntheses. In 1993, Holton7,8 reported the first total synthesis, which was closely followed by that of Nicolaou.9-12 Syntheses by Danishefsky,13 Wender,14,15 Mukiyama,16 Kuwajima17 followed, with the most recent synthesis coming in 2006 by Takahashi.18

III. Semisynthesis

As the total synthesis of Taxol cannot solve the problem of commercial supply, the semisynthesis of Taxol from 10-DAB provided a reasonable alternative. A key part of this four-step procedure, which was first recognized by Potier,19 is the relative reactivities of the four hydroxyl groups in 10-DAB. By studying the attempted acetylation of the four hydroxyl groups, Potier found that the C-7 hydroxyl was the most reactive followed by the C-10 hydroxyl, then the C-13 hydroxyl and finally, the C-1 hydroxyl, which was not acetylated under any conditions used. Using this information, a series of selective protections was developed (Scheme 9). First, the C-7 hydroxyl was selectively silylated to give 7-TES-10-DAB. Next, the C- 10 hydroxyl was acetylated using acetyl chloride in pyridine to give 7-TES-Baccatin III 61.5

Scheme 2. Synthesis of 7-TES-Baccatin III

Esterification of 7-TES-Baccatin III

Subsequent esterification of the C-13 hydroxyl group proved to be a challenge throughout the development of the semisynthesis due to its steric environment (Figure 2). The C-13 hydroxyl sits underneath the concave face of the baccatin skeleton. This would require the acylating agent to approach the baccatin from underneath.

Figure 2. Steric environment of C-13 hydroxyl 3

Unable to attach an intact side chain to the C-13 hydroxyl, Potier converted 7- Troc-baccatin III 6 to the cinnamoyl derivative 8 using cinnamic acid 7 in the presence of DCC and DMAP. Sharpless hydroxyamination with 9 followed to give 1:1 mixture of regioisomers 10 and 11. Carbamate 10 was converted to Taxol by removal of the t-Boc group with TMSI, followed benzoylation with BzCl and then removal of the 7-Troc with Zn/acetic acid.

Scheme 3. The First Semisynthesis of Taxol

In 1988, Green and Potier were the first to attach an intact side chain directly to a baccatin III derivative. The reaction between 7-TES-Baccatin III and acid 62 (Scheme 10) took place under very specific (DPC, DMAP) and somewhat harsh conditions (100 hours at 73oC). In the reaction, six equivalents of acid 62 were used, to give 80% yield at 50% conversion of the coupled product. While this is nowhere near suitable for commercial use, it was a significant step forward in the semisynthesis of Taxol.

Scheme 4. Green-Potier Esterification5

Methods for Synthesis of the C-13 Side Chain

There are several ways to synthesize the Taxol side chain. The following is a summary of those methods.

A) β-Phenylglycidates20-27

The first synthesis of the Taxol side chain was from cis-β-phenylglycidic acid 12, which was resolved and the corresponding ester was submitted to regioselective ammonolysis to give 14 (Scheme 5). Hydrolysis of 14 followed by benzoylation gave acid 15. Another route to acid 15 involves the regioselective opening of epoxide 12 with sodium azide or TMSI in the presence of zinc chloride to give 13.

Scheme 5. Synthesis of Taxol Side Chain from cis-β-Phenylglycidates

Azido acid 13 was then converted to the 2-butanoyl ester and was resolved enzymatically. Subsequent benzoylation followed by hydrogenation also completed the synthesis of acid 15. The side chain has also been synthesized from racemic trans-β-phenyl methyl glycidate 16, which was enzymatically converted the presence of i-BuOH to 22 and the 5

i-Butyl ester of its enantiomer 17. Methyl ester (-)22 was converted to azido ester 23 by successive treatment with diethylamine hydrobromide in the presence of diethylaluminum chloride and then sodium azide. The i-Butyl ester 17 was opened with sodium azide to give 18. Subsequent benzoylation followed by hydrogenation converted 18 to amide 19. The amide was then cyclized to give oxazoline 20, which was then opened with HCL, MeOH to give the methyl ester of the acid side chain 21.

Scheme 6. Synthesis of Taxol Side Chain from trans-β-Phenyl methyl glycidate

B) 4-Phenyl-1-Butene Derivatives28,29

The Taxol side chain has also been synthesized using a 4-phenyl-1-butene intermediate. Optically active phenyl glycine 24 was reduced with LAH followed by benzoylation to give amide 25. Subsequent Swern oxidation followed by treatment with vinyl magnesium bromide gave phenyl butane derivative 27. Protection of the secondary alcohol followed by oxidative cleavage of the olefin gave acid side chain 15a.

Scheme 7. Synthesis of Taxol side chain from 4-Phenyl-1-Butene Derivatives

C) Ketene Acetals30,31

The Taxol side chain has been synthesized asymmetrically from ketene acetals (Scheme 8). The Z-triethylsilyl ketene acetal 29 was reacted with chiral imine 28, with the use of chiral boron reagent 30, to give ester 31 after hyrolysis with HCl. Hydrogenolysis followed by benzoylation gave methyl ester 21 in 68% yield. Secondly, Z-triethylsilyl ketene acetal 34 was treated with imine 33, to give a mixture of syn diastereomers 35 and 36 with yields between 50-75%. The best ratio obtained was 10:1 in favor of the desired 35.

Scheme 8. Synthesis of Taxol side chain from Ketene Acetals

D) Glycolyl Sultam Enolates32

The N-acyl sultam 38 was synthesized from 37 in 97% yield. Imine 39 was then added to the lithium enolate of 38 at -78oC to give 40 with 99% d.e. The synthesis of the side chain was completed in 70% yield by hydrogen peroxide supported hydrolysis of 40

Scheme 9. Synthesis of Taxol side chain from Glycolyl Sultam Enolates

E) Thioester enolates33

The Taxol side chain has been synthesized by the aldol condensation between thioglycolate 43 and the chiral chromium carbonyl complex 42, which gave thioester 44 as a 95:5 mixture of anti:syn diastereomers in 93% yield. Removal of the silyl group and decomplexation of the chromium species gave thioester 45 in 63% yield. The thioester side chain derivative 46 was synthesized by inversion of configuration at the β carbon by formation of the azido ester. The thioester was then converted the methyl ester with thallium trinitrate (TTN) and the benzyl group was removed by hydrogenolysis to give the methyl ester Taxol side chain 47.

Scheme 10. Synthesis of Taxol side chain from Thioester Enolates

F) Asymmetric Oxaziridine-Mediated Hydroxylation34,35

The Taxol side chain has also been synthesized using chiral oxaziridines to introduce the C-2 hydroxyl group.The synthesis starts with sulfenimine 48, which is oxidized to the sulfinyl imine 50 with oxaziridine 49 in 72% yield and 88% ee. The ester 52 was synthesized in 74% yield by reaction of the sulfinyl imine with lithium enolate 51. The sulfinyl group was removed with trifluoroacetic acid. Benzoylation followed to give benzamide 53. The lithium enolate of 53 was formed with LDA and then reacted with (+)-camphorsulfonyl oxaziridine 54 to give methyl ester 55 and its anti-diastereomer in 58% yield. Another synthesis of the side chain begins with t-butyl cinnamate 56, to which was added the chiral lithium amide 57 and the resulting enolate was treated with oxaziridine 54 to give anti-ester 58. Hydrogenolysis of the ester followed by conversion to the methyl ester gave 53 in 96% yield. Benzoylation gave 60 in 96% yield. Although this synthesis gives the undesired isomer, the Taxol side chain can be prepared from this method because both enantiomers of the α-methyl benzylamine and oxaziridine 54 are commercially available.

Scheme 11. Synthesis of Taxol side chain via asymmetric hydroxylation

G) Β-Lactams

In our group, it was envisaged that β -lactams could deliver as admirable Taxol side chain precursors. It was anticipated that N-acyl-β-lactams could be an applicable means for installation of the C-13 side chain due to their planarity, along with the syn configuration of both the substituents on the ring. This would allow their approach to the C-13 hydroxyl on the baccatin to be less sterically hampered. Another reason why N- acyl-β-lactams were considered good candidates for introduction of the side chain is the ease in which they can be synthesized. They can be made via the Staudinger reaction in either racemic or asymmetric form (Scheme 12).

Scheme 12. Formation of β-Lactam by the Staudinger reaction

They have also been synthesized asymmetrically via an ester enolate-imine cycloaddition reaction (Scheme 13).

Scheme 13. Formation of β-Lactam by an ester enolate-imine cycloaddition

Preliminary results which involved the reaction of β-lactams such as 63a (PG = EE, TES, TBS or TIPS protected) with simple alcohols, have shown that in the presence of just pyridine no reaction took place. With the addition of DMAP, the EE and TES protected lactams reacted with benzyl alcohol to give the corresponding benzyl ester. However, for sterically hindered substrates, such as the C-13 hydroxyl on baccatin, the reaction had several limitations. High concentrations of the substrate (2M in pyridine), equimolar amounts of the expensive DMAP, and five equivalents of the β-lactam were needed for the reaction to proceed (Scheme 14).36

Figure 3. N-acyl-β-lactam

Moreover, highly activating acyl groups, such as the benzoyl group, were required. If a less activating group such as N-tert-butoxycarbonyl was used, almost no esterification product was formed.

Scheme 14. Esterification of 7-TES-baccatin III with N-acyl-β-lactams

Due to these limitations an alternate method was sought. After extensive experimentation, it was found that exposure of 7-TES-baccatin III to butyllithium at -45oC in THF, followed by the addition of (+)63c (Scheme 15) and allowing the reaction to warm to 0oC over a two hour period, gave the 2’,7-di-TES compound 64.37 Deprotection with HF/pyridine gave Taxol (1) in quantitative yield.

Scheme 15. Esterfication of 7-TES-baccatin III lithium alkoxide with β-lactam

Moreover, the lithium alkoxide was shown to react diastereoselectively with racemic β- lactams (Scheme 16).38 Depending on which β-lactam is used, the diastereoselectivity ranges between 3:1 and >100:1.36 This presents the opportunity to attach the chiral side chain of Taxol from an achiral source, which would negate the need to synthesize a chiral side chain or side chain surrogate.

Scheme 16. Diastereoselectivity of coupling reaction

The goal is to improve the selectivity of the reaction between 7-TES-baccatin III and β -lactam 65, which in THF gives a 3:1 ratio via the lithium alkoxide and form exclusively 2’-MOP-7-TES-baccatin III 65 upon reaction with 2 equivalents of the β - lactam (Scheme 17).

Scheme 17. Diastereoselective semisynthesis of Taxol

CHAPTER II. RESULTS and DISCUSSION

At the outset it was anticipated that the selectivity of the coupling reaction could be controlled by changing: (1) The solvent: solvation of the β -lactam and/or the 7-TES-baccatin III could affect the rate of reaction, hence altering the selectivity. (2) The counterion: by changing the metal on the C-13 alkoxide, the selectivity could be altered due to the reactivity of the metal alkoxide. The number of coordination sites and the size of the metal should also affect the reactivity of the alkoxide with the β- lactam. (3) Coordinating ligands: coordination of chiral and achiral ligands to the metal alkoxide should alter the chemical and/or steric environment of the alkoxide, thus altering the reactivity towards the β-lactam. Before the investigation into the diastereoselectivity could begin, the starting materials needed to be synthesized. The synthesis of β-lactam 65 is shown in Scheme 18.39,40 Acid chloride 70 was synthesized in two steps from glycolic acid (69). β-Lactam 73 was synthesized via the Staudinger reaction between 70 and imine 72. The PMP group was removed by CAN oxidation followed by deacetylation to give 74. The hydroxyl group of 74 was then protected as a methoxy propyl ether (MOP), followed by benzoylation of the nitrogen to give β-lactam 65.

Scheme 18. Synthesis of β-lactam 32

Conversion of 10-DAB to 7-TES-baccatin III required two steps (Scheme 19). First, the C-10 hydroxyl was selectively acetylated using acetic anhydride in the presence 41 of catalytic (10 mol%) CeCl3, then the C-7 hydroxyl was selectively silylated with TESCl.

Scheme 19. Synthesis of 7-TES-baccatin III

As stated previously, the reaction between 7-TES-baccatin III and racemic β- lactam 65 proceeds diastereoselectively to give a 3:1 ratio of taxol to epi-taxol. This selectivity is believed to derive from the lithium alkoxide at C-13, with the lithium ion also coordinating to the C-4 acetate. This forces the β-lactam to approach the baccatin from underneath the concave face, with both substituents facing down. Two possible approaches of the β-lactam 65 could then be envisaged as depicted in Figure 4, leading to the two epimers.

Figure 4. Diastereoselectivity of C-13 Lithium alkoxide with racemic β-lactam

I. Solvent effects on diastereoselectivity

Studying the solvent effects on the diastereoselectivity of the coupling reaction proved to be somewhat difficult due to to the low solubility of the 7-TES-baccatin III in most solvents. This problem was overcome in most instances by longer reaction times made possible by the use of a constant temperature bath.

A) Ethereal and Non-Aromatic Solvents

Several ethereal and non-aromatic solvents were used. Few solvents showed any effect on selectivity, and even the affects that were observed were modest. The best selectivity (5:1 in favor of the Taxol analog) was observed with 1,3 dioxane.

Table 1. Diastereoselectivity in Ethereal and Non-Aromatic Solvents

Solvent Time Conversion 66 : 67 68

THF 5hr 100% 3.2 : 1 3% Ether 9hr 53% 4 : 1 4% N-methyl- 6hr 82% 2.8 : 1 3% morpholine DME 12hr 70% 3 : 1 4% DCM 9hr 48% 1.6 : 1 3% 1,3 – Dioxane 5hr 80% 4.5 : 1 3% TMTHF 8hr 88% 2.6 : 1 8% DMM 12hr 51% 2.8 : 1 2%

B) Aromatic Solvents

With the benzoyl protected β-lactam 65, the selectivity is 3:1 in favor of taxol in THF. The t-Boc protected β -lactam 75 (Figure 5) has shown to have much greater selectivity giving exclusively the 2’R, 3’S isomer.37,38,42

Figure 5. t-Boc protected β-lactam

The difference in selectivity could possibly come from the steric bulk of the t- Boc group. With this premise it was envisaged that the sterics of the benzoyl group on 65 could be increased via π-stacking interactions by the use of aromatic solvents. The results obtained using some aromatic solvents are shown in Table 2.

Table 2. Effect of aromatic solvents on the diastereoselectivity

Solvent Time Conversion 66 : 67 68 Toluene 12hr 74% 3.2 : 1 2% Anisole 20hr 77% 2.4 : 1 3% Fluorobenzene 24hr 82% 8.8 : 1 4% Trifluorotoluene 20hr 70% 5.7 : 1 3% Pyridine 5hr 79% 2.7 : 1 5% Chlorobenzene 24hr 73% 4.5 : 1 2% Bromobenzene 24hr 81% 3.6 :1 2% m-Methoxyanisole 24hr 58% 2.9 : 1 3%

The only solvents which improved the selectivity were the fluorinated aromatic solvents, which could be the result of a π-stacking interaction between the benzoyl group and the electron deficient phenyl ring of fluorobenzene or trifluorotoluene. The greater selectivity could also be explained simply by the rate of reaction. The reaction is significantly slower in these solvents, therefore giving better selectivity.

II. Counterion

It was anticipated that by changing the counterion the C-13 alkoxide the selectivity of the coupling reaction could be enhanced. This change in selectivity could possibly come from altering the reactivity of the C-13 alkoxide, which is directly dependent upon the counterion. Other factors that could control the reactivity are the size of the counterion and the number of coordination sites available. The acidity of the counterion, which will affect the ability of the β -lactam to coordinate to it, could also allow one enantiomer to react faster than the other thus possibly altering the selectivity.

A) Lithium

The lithium alkoxide at C-13 gives a 3:1 ratio in THF, irrespective of the base used for deprotonation, which suggests that the base byproducts have no role in the reaction. As stated previously, this selectivity is brought about by the coordination of the metal cation with the C-4 acetate (Figure 4). Further evidence of this can be seen from the addition of HMPA to the reaction (Table 3). The HMPA captures the lithium cation leaving the naked alkoxide equally vulnerable to both enantiomers of β -lactam 65, providing little selectivity.

Table 3. Selectivity of Lithium Alkoxides

Base Time Conversion 66 : 67 68 LHMDS 5hr 100% 3 : 1 3% BuLi 5hr 97% 2.7 : 1 3% LDA 5hr 100% 3.2 : 1 2% LTMP 5hr 90% 2.7 : 1 4% LHMDS/HMPA 4hr 70% 0.8 : 1 0% 19

The coordination to the C-4 acetate is crucial to the selectivity, but what role does the metal play in terms of coordination with the β-lactam? Multiple equivalents of lithium were used to determine if one enantiomer of 65 has a stronger coordination to the metal, thus enhancing the selectivity (Table 4). Increasing the amount of lithium present in the reaction gave no change in selectivity. Secondly, it was envisaged that using a more acidic lithium species would increase the coordination with 65. The use of 1 equivalent of

LiClO4 gave no change in reactivity. Increasing the amount of LiClO4 used in the reaction (up to 5 equivalents) showed only a slight increase in selectivity.

Table 4. Selectivity of Lithium Alkoxide with an Excess of Lithium

Base Time Conversion 66 : 67 68 MeLi - LiBr 7hr 67% 6.4 : 1 0% MeLi – LiI 12hr 94% 3 : 1 4% BuLi - LiBr 7hr 91% 3.8 : 1 4% BuLi – LiCl 7hr 95% 3.2 : 1 3% LDA – LiBr 7hr 93% 4.5 : 1 5% LDA – LiCl 7hr 92% 3.2 : 1 4% LHMDS – LiBr 7hr 81% 4.4 : 1 5% LHMDS - LiCl 4hr 75% 3.4 : 1 4%

LHMDS - LiClO4 4hr 78% 3.4 : 1 4%

B) Sodium

The C-13 sodium alkoxide lowered the selectivity to 2:1 ratio in favor of the taxol analog (Scheme 20). This lowered selectivity could be explained in terms of hardness and

softness. The C-13 alkoxide is a hard base and, while the sodium cation is considered a hard acid, it is much softer than lithium. This difference between the sodium and oxygen makes the alkoxide more reactive, leading to lower selectivity.

Scheme 20. Sodium alkoxide

The sodium alkoxide was also formed using toluene, 1,3-dioxane, pyridine and fluorobenzene as solvents. There was no change in selectivity.

C) Potassium

The potassium cation is a much softer acid than sodium, which is consistent with the 1:1 ratio observed with a potassium counterion (Scheme 21). Due to this difference in hardness between the potassium cation and the oxygen of the alkoxide, the C-13 oxygen is essentially a bare alkoxide. This alkoxide is so reactive that there is no selectivity.

Scheme 21. Potassium alkoxide

The potassium alkoxide was also formed using t-BuOK as the base and toluene, benzene, fluorobenzene and 1,3–dioxane as the solvent. There was no change in selectivity.

D) Magnesium

It was anticipated that a magnesium alkoxide at C-13 would exhibit a difference in selectivity due to its divalency. By altering the substituent on the magnesium alkoxide, the selectivity was immensely affected. Three different types of magnesium alkoxides were investigated: (1) halide-magnesium alkoxides (2) alkyl-magnesium alkoxides and (3) amide-magnesium alkoxides.

Halo-Magnesium Alkoxides

Halo-magnesium alkoxides were generated at C-13 by either transmetallation of a lithium alkoxide with MgBr2 or deprotonation with Grignard reagents (Table 5). The bromo and chloro-magnesium alkoxides favor the undesired diastereomer 67 at a ratio of approximately 2.5 : 1.

Table 5. Selectivity of Halo-Magnesium Alkoxides

Base Solvent Time Conversion 66 : 67 68

LHMDS/MgBr2 THF 14hr 65% 1 : 4.4 22% i-PrMgCl THF 14hr 82% 1 : 2.3 5% EtMgBr THF 14hr 70% 1 : 2.6 5% PhMgCl THF 12hr 88% 1 : 2.4 4% MeMgI THF 14hr 70% 2.5 : 1 0% i-PrMgCl-LiCl THF 14hr 90% 1 : 4 21% i-PrMgCl 1,3-dioxane 14hr 85% 1 : 2.5 4% EtMgBr 1,3-dioxane 14hr 78% 1 : 2.5 4% PhMgCl 1,3-dioxane 14hr 90% 1 : 2.2 3% 22

Table 5 cont. from p.21 MeMgI 1,3-dioxane 14hr 72% 2.4 : 1 0% i-PrMgCl pyridine 14hr 87% 1 : 2.5 4% EtMgBr pyridine 14hr 83% 1 : 2.3 5% PhMgCl pyridine 14hr 89% 1 : 2 3% MeMgI pyridine 14hr 76% 2.5 : 1 0%

Figure 6. Diastereoselectivity of C-13 Halo-Magnesium alkoxide with racemic β-lactam

It is envisaged that the magnesium coordinates to the acetate at C-4 with the halide in the beta orientation as shown in Figure 6. This forces the β-lactam to approach the C-13 alkoxide from the backside underneath the concave face. This approach is difficult for the desired enantiomer. Depending on which face approaches, there are strong steric interactions between the phenyl ring, MOP protected hydroxyl, and benzoyl group of the β -lactam and the C-18 methyl and C-7 TES group on 7-TES-baccatin III (Figure 6). Using MeMgI as the base, the selectivity reversed to favor diastereomer 66. This may result from the Grignard forming a complex with THF, shifting the equilibrium towards the dialkyl magnesium (Scheme 22).

Scheme 22. Formation of Dialkyl Magnesium from alkylmagnesium iodides43

In this case, a methyl-magnesium alkoxide may be formed instead of an iodo- magnesium alkoxide.

Alkylmagnesium Alkoxides44

Alkylmagnesium alkoxides were synthesized by deprotonating the C-13 hydroxyl with the corresponding dialkylmagnesium reagent (Table 6). The use of the alkylmagnesium alkoxides favors the formation of 66 at a 66:67 ratio of approximately 2:1.

Table 6. Selectivity of Alkylmagnesium Alkoxides

Base Time Conversion 66 : 67 68

Me2Mg 10hr 70% 2.3 : 1 0%

Et2Mg 12hr 80% 2 : 1 0%

i-Pr2Mg 10hr 67% 2.5 : 1 0%

Bu2Mg 10hr 65% 2.3 : 1 0%

Ph2Mg 12hr 85% 2.9 : 1 0%

Figure 7. Diastereoselectivity of C-13 Alkylmagnesium alkoxide with racemic β-lactam 32

It is proposed that the magnesium on the C-13 alkoxide is coordinating to the acetate at C-4 with the alkyl group in the alpha orientation under the hydrophobic portion of the 7-TES-baccatin III (Figure 7), which allows the β -lactam to approach from underneath the concave face, similar to that of the lithium alkoxide and therefore favoring the desired diastereomer 66.

Amido-Magnesium Alkoxides45

The magnesium bis-amides (Figure 8) were synthesized by treating Bu2Mg with two equivalents of the corresponding amine (Scheme 23). These amides were used to deprotonate the C-13 hydroxyl forming the amido-magnesium alkoxides (Table 7). The selectivity observed using the amido-magnesium alkoxides was similar to that of the alkyl-magnesium alkoxides, favoring the formation of 66 at a ratio of approximately 2:1.

Scheme 23. Synthesis of Magnesium Bis-Amides

Figure 8. Magnesium Bis-Amides

The reason for this selectivity is postulated to be similar to that for the alkylmagnesium, as illustrated in Figure 7, with the amide lying under the hydrophobic portion of the baccatin. This allows the lactam to approach from the beta position under the concave face of the baccatin.

Table 7. Selectivity of Amide-Magnesium Alkoxide

Amide Time Conversion 66 : 67 68 76 6hr 52% 2.3 : 1 16% 77 6hr 49% 2.1 : 1 15% 78 6hr 55% 2.5 : 1 13%

E) Lanthanide Alkoxides

It was contemplated that the use of lanthanide alkoxides would alter the selectivity of the coupling reaction due to their size and number of coordination sites available. The lanthanide alkoxides were synthesized by first forming a lithium alkoxide at C-13, then transmetallating with the corresponding lanthanide halide (Table 8).

Table 8. Selectivity of Lanthanide Alkoxides

Lanthanide Solvent Time Conversion 66 : 67 68

SmCl3 THF 6hr 70% 3.4 : 1 4%

EuCl3 THF 8hr 73% 4.2 : 1 5%

LaCl3 THF 8hr 80% 3.3 : 1 3%

YbCl3 THF 8hr 85% 3.8 : 1 3%

CeCl3 THF 8hr 60% 4 : 1 0%

CeI3 THF 12hr 90% 8 : 1 1%

SmCl3 1,3-dioxane 8hr 75% 3.2 : 1 4%

EuCl3 1,3-dioxane 8hr 78% 3.7 : 1 3%

LaCl3 1,3-dioxane 8hr 70% 3.1 : 1 2%

YbCl3 1,3-dioxane 8hr 89% 2.7 : 1 0%

CeCl3 1,3-dioxane 8hr 64% 3.9 : 1 0%

CeI3 1,3-dioxane 12hr 93% 9.3 : 1 0%

SmCl3 pyridine 8hr 66% 3 : 1 2%

EuCl3 pyridine 8hr 81% 3.3 : 1 3%

LaCl3 pyridine 18hr 83% 2.8 : 1 3%

YbCl3 pyridine 8hr 77% 2.9 : 1 3%

CeCl3 pyridine 8hr 62% 3.8 : 1 0%

CeI3 pyridine 12hr 87% 6.7 : 1 2%

The cerium alkoxide formed from transmetallation with CeI3 gave the best ratio at approximately 8:1. A possible explanation for this increase in selectivity could be due to a stronger coordination of the desired enantiomer of 65 with cerium, thus allowing it to

react faster. It has been shown that at low conversion (less than 50%), the desired diastereomer was exclusively formed (Figure 9).

Figure 9. D.E. vs Reaction Conversion

As the concentration of the desired enantiomer decreases, relatively more of the undesired enantiomer is available for reaction, thus at 90% conversion the ratio dropped to approximately 8:1. In the case where LHMDS is solely used as a base, the ratio varies from 6 : 1 at 30% conversion to 3 : 1 at 100% conversion, thus confirming that the cerium halide allows one enantiomer of 65 to react faster then the other.

F) Alkyl – Lanthanide Alkoxides

It was envisaged that the use of alkyl lanthanide alkoxides would alter the selectivity of the coupling reaction due to the increase in steric bulk around the metal. This steric increase could affect the approach of the β-lactam, possibly increasing the rate of reaction of one enantiomer over the other. The alkyl groups should also alter the

acidity of the metal, therefore altering its coordination with the β-lactam, which should change the selectivity.

Scheme 24. synthesis of alkyl lanthanides

The mono and dialkyl lanthanide salts were synthesized by treating the corresponding lanthanide halide with BuLi at low temperature (Scheme 24). The alkyl lanthanide alkoxide was then formed by transmetallating the C-13 lithium alkoxide with the alkyl lanthanide halide (Table 9).

Table 9. Alkyl -Lanthanide Alkoxides

Alkyl Lanthanide Solvent Conversion 66 : 67 68

BuLaCl2 pyridine 72-84% 6-9 : 1 0%

Bu2LaCl THF 75-88% 7-11 : 1 0%

BuCeCl2 THF 86% 7 : 1 0%

Bu2CeCl THF 89% 9 : 1 0%

The results of the mono and dialkyl-lanthanum alkoxides were not reproducible and gave a range of 6-11: 1 in favor of 66. Increasing the steric bulk on the metal gave no significant change in selectivity over the lanthanum – halide alkoxide. The alkyl-cerium halide alkoxide favored 66 at a 7:1 ratio, while the dialkyl-cerium alkoxide gave a 9:1 ratio. These results also showed no difference from the cerium-halide alkoxides.

G) Ammonium

It was envisaged that an ammonium alkoxide would improve the selectivity due to the steric bulk of the ammonium ion, which might inhibit the reaction of the β-lactam. The ammonium alkoxides were synthesized by forming a lithium alkoxide at C-13 with LHMDS followed by addition of the ammonium salt giving the lithium salt as the byproduct. The ammonium alkoxides showed no difference in selectivity from that of lithium (Table 10).

Table 10. Selectivity of Ammonium Alkoxides

Ammonium Solvent Time Conversion 66 : 67 68 Halide BnNEt3Cl THF 6hr 51% 2.8 : 1 6%

Bu4NBr THF 8hr 47% 2.1 : 1 4%

Me4NBr THF 8hr 44% 1.7 : 1 3%

Me4NCl THF 8hr 55% 3 : 1 3%

Bu4NOAc THF 8hr 40% 1.5 : 1 2%

BnNEt3Cl 1,3-dioxane 8hr 45% 2.4 : 1 4%

Bu4NBr 1,3-dioxane 8hr 51% 1.6 : 1 2%

Me4NBr 1,3-dioxane 8hr 48% 1.5 : 1 3%

Me4NCl 1,3-dioxane 8hr 51% 2.5 : 1 2%

Bu4NOAc 1,3-dioxane 8hr 47% 1.4 : 1 4%

III. Coordinating Ligands

It was anticipated that the use of coordinating ligands could affect the selectivity of the coupling reaction by either creating steric bulk around the metal alkoxide, thus inhibiting the reactivity of the β-lactam, or enhancing the chirality by allowing only one enantiomer of 65 to approach. The syntheses of these coordinating bases (Figure 10) are shown in Scheme 25. It was anticipated that upon deprotonation of the C-13 hydroxyl with these bases, the corresponding amine, diamine or alkoxyamine, which were purchased from Sigma- Aldrich, would then coordinate to the metal counter ion. This coordination would thus affect the approach of the β-lactam altering the selectivity.

Scheme 25. Synthesis of Coordinating Bases

Figure 10. Bases used for ligand Coordination

The best selectivity came from alkoxyamine 80 (Table 11), which gave an 8:1 ratio in favor of 66. In general, the alkoxyamines gave better selectivity towards the

taxol analog, possibly due to the ability of the oxygen to better coordinate to the metal cation.

Table 11. Selectivity of Coordination Ligands

Base Solvent Time Conversion 66 : 67 68 79 THF 4hr 93% 3.1 : 1 3% 80 THF 5hr 95% 7.3 : 1 4% 81 THF 5hr 70% 7.4 : 1 3% 82 Toluene 5hr 70% 3.1 : 1 5% 83 THF 5hr 91% 3.2 : 1 8% 84 THF 5hr 75% 4 : 1 4% 85 THF 5hr 90% 3.1 : 1 3% 86 THF 14hr 80% 1 : 2.3 4% 87 THF 14hr 82% 1 : 2.5 4% 79 1,3-dioxane 4hr 90% 3 : 1 5% 80 1,3-dioxane 5hr 94% 6.4 : 1 5% 81 1,3-dioxane 5hr 76% 5.6 : 1 3% 83 1,3-dioxane 5hr 87% 2.8 : 1 4% 84 1,3-dioxane 5hr 81% 5 : 1 3% 85 1,3-dioxane 5hr 86% 3.6 : 1 3% 86 1,3-dioxane 14hr 84% 1 : 2.2 4% 87 1,3-dioxane 14hr 78% 1 : 2.5 4% 79 pyridine 4hr 87% 3.4 : 1 3%

Table 11 cont. from p. 32 80 pyridine 5hr 91% 6.8 : 1 5% 81 pyridine 5hr 68% 6.1 : 1 4% 83 pyridine 5hr 89% 2.4 : 1 4% 84 pyridine 5hr 79% 4.4 : 1 4% 85 pyridine 5hr 83% 3 : 1 4% 86 pyridine 14hr 79% 1 : 2 3% 87 pyridine 14hr 84% 1 : 2.4 3%

IV. Conclusion

In conclusion, the above studies have shown that the diastereoselectivity of the coupling reaction between 61 and 65 can be affected through the use of different counter ions, coordinating ligands and solvents. The diastereoselectivity of the reaction was improved from 3:1 to 8:1. This improvement was brought about first by the use of fluorinated aromatic solvents. A diiodo-cerium alkoxide also improved the ratio to 8:1. Lastly, the use of bases 80 and 81 improved the ratio to the same extent. The use of a magnesium alkoxide in the coupling reaction has shown promise due to its wide range of selectivity, as does the use of cerium alkoxides.

Chapter III: Experimental

General Information. All reactions were carried out under an inert atmosphere of dry nitrogen in oven or flame-dried glassware. Proton magnetic resonance spectra were recorded at 300, 400, and 500 MHz on Varian Mercury, and Varian Unity Inova spectrometers, respectively. All chemical shifts were reported in δ units relative to tetramethylsilane. Analytical thin-layer chromatography (TLC) was performed using pre-

coated TLC plates with silica Gel 60 F254 (E. Merck no. 5715-7). Flash column chromatography was performed using 40-60 µm (400-230 mesh) silica gel (E. Merck no.

9385-9) as the stationary phase. Tetrahydrofuran (THF), ether (Et2O), benzene (PhH),

toluene (PhCH3), Dimethoxyethane (DME), 1,3-Dioxane, 2,2,4,4-Tetramethyl tetrahydrofuran (TMTHF), Dimethoxymethane (DMM), Anisole, m-Methoxyanisole were dried by refluxing over Na-benzophenone in a continuous still under an atmosphere

of nitrogen. Dichloromethane (CH2Cl2), di-iso-propylamine, pyridine, triethylamine, and

acetonitrile (CH3CN) were refluxed over calcium hydride in a continuous still under an atmosphere of nitrogen. Chlorotriethylsilane (TESCl), was distilled from calcium hydride under an inert atmosphere of dry nitrogen and stored over calcium hydride.

Fluorobenzene and Trifluorotoluene was distilled from P2O5 and stored over 3 Angstrom molecular sieves prior to use.

Preparation of β-Lactam 32

Preparation of 35. Glycolic acid 34 (50g, 65.7 mmol) and 0.1mL of pyridine were added to a 500mL RBF. The flask was then cooled in an ice bath and 126mL of acetyl chloride (2.7eq, 1.78mol) was added dropwise. The mixture was allowed to stir for 15 min. The mixture was then heated at reflux to dissolve the solid formed. The excess acetyl chloride was then removes by simple distillation. Then 62.3 mL of thionyl chloride (1.3eq, 85.5 mmol) was added dropwise and the reaction was refluxed for 1 hr. The excess thionyl chloride was then removed by distillation under reduced pressure. Acid chloride 35 was then purified by distillation under reduced pressure to give 73.5g (83%) of product. Analytical data matches that which was previously reported.46 Preparation of 37. p-Anisidine (35g, 28.4 mmol) and 50mL of benzene was placed in a 100mL RBF. Then 29.9mL of benzaldehyde (1.1 eq, 31.2mmol) was added and the reaction mixture was stirred for 10min. Then benzene was removed and the crude solid was purified by recrystallization from hexane/DCM (3:1) to give 53.7g (89%) of the imine. Analytical data matches that which was previously reported.47 Preparation of 38. Imine 37 (50g, 23.7mmol) was dissolved in 150mL of DCM. and 49.3 mL of Et3N (1.5eq, 35.5mmol) was added dropwise. The reaction mixture was cooled to -10°C and acid chloride 35 (in 150mL DCM) was added dropwise over 1hr. After the addition the RM was warmed to rt and was allowed to stir for 6hr. The reaction was quenched with saturated aqueous NaHCO3. The organic layer was then separated and the aqueous phase was extracted with DCM (3X). The combined organic phase was washed with saturated aqueous NaHCO3, brine, dried over sodium sulfate, filtered, and concentrated. The crude solid was purified by recrystallization from hexane/EtOAc (3:1) to give 69.3g (94%) of the β-lactam. Analytical data matches that which was previously reported.46 Preparation of 41. β -Lactam 38 (20g, 64.2mmol) was dissolved in 330mL of

CH3CN. The solution was then cooled to -10°C and a 0.9M aqueous CAN solution (250mL, 3eq) was added dropwise. The RM was allowed to stir for 30min, diluted with

EtOAc and quenched with saturated aqueous NaHCO3. NaHSO3 (66g, 10eq) was added and the RM was stirred for 30min, then filtered and the organic layer was separated and the aqueous phase was extracted with EtOAc (3X). The combined organic phase was washed with saturated aqueous NaHCO3, brine, dried over sodium sulfate, filtered, and concentrated. The crude solid was purified by recrystallization from hexane/Acetone (3:1) to give 11.7g (89%) of the N-H β-lactam. Analytical data matches that which was previously reported.48 The N-H β -lactam (11.7g, 57mmol) was then dissolved in 200mL of THF and added dropwise to a KOH/THF solution at 0°C. The RM was allowed to stir for 30min and quenched with saturated aqueous NaHCO3. The organic layer was then separated and the aqueous phase was extracted with EtOAc (3X). The combined organic phase was washed with saturated aqueous NaHCO3, brine, dried over sodium sulfate, filtered, and concentrated. The crude solid was purified by recrystallization from hexane/EtOAc (4:1) to give 8.98g (97%) of β-lactam 41. Analytical data matches that which was previously reported.49 Preparation of 32. β-Lactam 41 (8.98g, 55mmol) was dissolved in 70mL of THF and the solution was cooled to -30°C and 2-methoxypropene (17.2mL, 2.5eq) was added dropwise and the mixture was stirred for 10min. Then PTSA (0.01eq of 0.1M in THF) was added dropwise and the RM was stirred for 30min. The resulting solid was dissolved in DCM and the reaction was quenched with Et3N (8mL). The solution was then washed with saturated aqueous NaHCO3 and the organic layer was then separated and the aqueous phase was extracted with DCM (3X). The combined organic phase was washed with saturated aqueous NaHCO3, brine, dried over sodium sulfate, filtered, and concentrated. The crude solid was purified by recrystallization from toluene to give 12.26 (95%) of the MOP protected β-lactam. The MOP protected β-lactam (12.26g, 52.1mmol) and DMAP (635mg, 0.1eq) was dissolved in 140mL of DCM and Et3N (14.5mL, 2eq) was added. The RM was cooled to 0°C and BzCl (7.3mL, 1.2eq) was added dropwise. The reaction was stirred for 30min, diluted with hexane/EtOAc (2:1) and quenched with saturated aqueous NaHCO3. The organic layer was then separated and the aqueous phase was extracted with EtOAc (3X).

The combined organic phase was washed with saturated aqueous NaHCO3, brine, dried 36

over sodium sulfate, filtered, and concentrated. The crude solid was purified by recrystallization from hexane/EtOAc (3:1) to give 16.03g (91%) of β-lactam 32.

Preparation of 7-TES-Baccatin III

10-DAB 2 (4g, 7.3mmol) and CeCl3 (180mg, 0.1eq) were dissolved in 60mL of THF. Acetic anhydride (6.8mL, 10eq) was added dropwise, and the RM was stirred for

5hr at rt. The reaction was quenched with saturated aqueous NaHCO3.The organic layer was then separated and the aqueous phase was extracted with EtOAc (3X). The combined

organic phase was washed with saturated aqueous NaHCO3, brine, dried over sodium sulfate, filtered, and concentrated. The crude solid was purified by recrystallization from hexane/EtOAc (4:1) to give 4.15g (96%) of baccatin III. Analytical data matches that which was previously reported.50 The baccatin III (4.15g, 7.1mmol) and imidazole (4.71g, 10eq) was dissolved in 12mL of DMF and diluted with 48mL of THF. Then TESCl (3.5mL, 1.5eq) was added and the RM was stirred at rt for 30min and quenched with saturated aqueous

NaHCO3.The organic layer was then separated and the aqueous phase was extracted with

EtOAc (3X). The combined organic phase was washed with saturated aqueous NaHCO3, brine, dried over sodium sulfate, filtered, and concentrated. The crude solid was purified by recrystallization from hexane/EtOAc (3:1) to give 4.60g (94%) of 7-TES-baccatin III 27. Analytical data matches that which was previously reported.51

Coupling Reaction

I. General Procedure

7-TES-Baccatin III (100mg, 0.14mmol) was dissolved in a solvent (see Tables 1- 2) and cooled to -45°C. Then 1.1eq of base (see Tables 3-7 and 10) was added and the RM was stirred for 30min. The β -lactam (2.1eq, 0.3mmol) was added as a solution in solvent (Tables 1-2). The reaction mixture was allowed to stir for a certain length of time

(Tables 3-7, 10). The reaction was quenched with saturated aqueous NaHCO3.The organic layer was then separated and the aqueous phase was extracted with EtOAc (3X).

The combined organic phase was washed with saturated aqueous NaHCO3, brine, dried over sodium sulfate, filtered, and concentrated to give a white solid. The ratio of diastereomers was determined by NMR.

II. Procedure for Transmetallation

7-TES-Baccatin III (100mg, 0.14mmol) was dissolved in solvent (see Tables 5, 8- 9) and cooled to -45°C. Then 1.1eq of base (see Tables 5, 8-9) was added and the RM was stirred for 30min. Then 1.1eq of a metal halide (Table 5, 8) or ammonium halide (Table 9) was added as a solution in solvent (Table 5, 8-9) and the mixture was stirred for 30min. The β-lactam (2.1eq, 0.3mmol) was added as a solution in solvent (Tables 5, 8-9) and the reaction mixture was allowed to stir for a certain length of time (Tables 5, 8-9).

The reaction was quenched with saturated aqueous NaHCO3.The organic layer was then separated and the aqueous phase was extracted with EtOAc (3X). The combined organic phase was washed with saturated aqueous NaHCO3, brine, dried over sodium sulfate, filtered, and concentrated to give a white solid. The ratio of diastereomers was determined by NMR.

Appendix

1 400 MHz H-NMR Spectrum of Compound 72 in CDCl3 p.40

1 400 MHz H-NMR Spectrum of Acid Chloride 70 in CDCl3 p.41

1 400 MHz H-NMR Spectrum of β-Lactam 73 in CDCl3 p.42

1 400 MHz H-NMR Spectrum of Nitrogen Deprotected β-Lactam in CDCl3 p.43

1 400 MHz H-NMR Spectrum of β-Lactam 74 in CDCl3 p.44

1 400 MHz H-NMR Spectrum of MOP Protected β-Lactam in CDCl3 p.45

1 400 MHz H-NMR Spectrum of β-Lactam 65 in CDCl3 p.46

1 400 MHz H-NMR Spectrum of Baccatin III in CDCl3 p.47

1 400 MHz H-NMR Spectrum of 7-TES-Baccatin III in CDCl3 p.48

1 400 MHz H-NMR Spectrum of 2’-MOP-7-TES-Taxol (66) in CDCl3 p.49

1 400 MHz H-NMR Spectrum of 2’-MOP-7-TES-epi-Taxol (67) in CDCl3 p.50

1 400 MHz H-NMR Spectrum of 13-Benzoate Baccatin III (68) in CDCl3 p.51

3 CDCl in

72 Imine

NMR Spectrum of - H 1 400 MHz

3 in CDCl

70 Acid Chloride

NMR Spectrum of - H 1 400 MHz

3 in CDCl

73 Lactam - β

NMR Spectrum of - H 1 400 MHz

3 in CDCl Lactam - β

Nitrogen Deprotected NMR Spectrum of - H 1 400 MHz

3 in CDCl

Lactam - β

NMR Spectrum of - H 1 400 MHz

3 in CDCl

Lactam - β

NMR Spectrum of MOP Protected - H 1 400 MHz

3 in CDCl

Lactam - β

NMR Spectrum of - H 1 400 MHz

3 in CDCl Baccatin III

NMR Spectrum of - H 1 400 MHz

3 in CDCl Baccatin III - TES - 7

NMR Spectrum of - H 1 400 MHz

3 CDCl in ) 66 Taxol ( - TES - 7 - MOP - 2’ NMR Spectrum of - H 1 400 MHz

3 in CDCl

) 7 6 Taxol ( - epi - TES - 7 -

MOP - 2’ NMR Spectrum of - H 1 400 MHz

3 in CDCl

) 68

Benzoate Baccatin III ( - 13 NMR Spectrum of - H 1 400 MHz

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BIOGRAPHICAL SKETCH

Joshua W. Lee was born in Louisville, Kentucky on April 14, 1980. He received his B.S. degree in Chemistry in April 2003 from the University of West Florida in Pensacola, Florida. During the fall 2003, he joined Florida State University in Tallahassee, FL where he worked under the supervision of Professor Robert A. Holton. He completed his graduate studies and received his M.S. degree in April 2008.