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Organic Chemistry 570 CHIMIA 2012, 66, No. 7/8 Organic chemistry doi:10.2533/chimia.2012.570 Chimia 66 (2012) 570–605 © Schweizerische Chemische Gesellschaft OrganicChemistry Organic Chemistry Organic Chemistry,Talk 358 Organic Chemistry,Talk 359 Screening of Chiral Organocatalysts for the Aldol ReactionbyMass AConcise Organocatalytic Approachfor the Spectrometric Monitoring of the Retro Reaction Stereoselective FormalSynthesis of AnachelinH Florian Bächle,Andreas Pfaltz* Suman De Sarkar andKarlGademann* University of Basel, St. Johanns-Ring 19, CH-4056 Basel, Switzerland DepartmentofChemistry, UniversityofBasel,St. Johanns-Ring 19, CH-4056 Basel, Switzerland Recently, our group developed anew high throughput screening method for the determination of the intrinsic enantioselectivity of chiral catalysts for the 1 Pd-catalyzed allylic substitution based on electrospray mass spectrometry The iron chelator anachelin is an important secondary metabolite for cya- and mass-labeled quasi-enantiomeric substrates [1]. As well, this method nobacteria Anabaenacylindrica exhibiting dualrole of both self-growth ac- was successfully applied to organocatalyzed asymmetric Diels-Alder [2] and celerationand growth inhibition of competing green algae. Thus we decided Michael reactions [3]. Monitoring the back reaction, the ratio of the detected to investigate the specificbioactivityofdifferentfragments to getaclear intermediates reflects the enantioselectivity of the corresponding forward insight intothe dualmodeofactionofthe complex naturalproduct. Herein reaction. we presentaconcise route for the asymmetric synthesis of polyketidechain Herein, we present our results for the application of this method to organo- fragment. Starting from N-Boc-L-serine the synthesis comprises metalcata- catalyzed aldol reactions. In contrast to our previous studies in which the lyzedasymmetric allylation on GarneraldehydefollowedbyGrubbs me- iminium ion was the intermediate for ESI-MS analysis, the adol reactions tathesis.The crucial part of the synthesis is the one-pot organocatalytic proceed via enamines which are more challenging to visualize. epoxidation andafollow-upesterification by acarbene catalyzed internal redox process.2 Finallyamidation andremoval of protectinggroups com- plete the stereoselective formal synthesis of thismetabolite. [1] For areview see: C. Müller, C. Markert, A. Teichert, A. Pfaltz, Chem. [1]K.Gademann, Y. Bethuel, Org. Lett. 2004, 6,4707; K. Gademann, Y. Commun. 2009,1607. Bethuel, Angew.Chem.Int. Ed. 2004, 43,3327. [2] A. Teichert, A. Pfaltz, Angew. Chem. Int. Ed. 2008, 47,3360. [2]H.Jiang, B. Gschwend, L. Albrecht, K. A. Jørgensen, Org. Lett. 2010, [3] I. Fleischer, A. Pfaltz, Chem. Eur. J. 2010, 16,95. 12,5052. OrganicChemistry OrganicChemistry Organic Chemistry,Talk 360 Organic Chemistry,Talk 361 Mechanistic Insights into Electrophilic Trifluoromethylations with Hy- ChemicalProtein Synthesis using α-Ketoacid–Hydroxylamine (KAHA) pervalent Iodine Reagents Ligation with 5-Oxaproline N. Santschi, N. Hauser, A. Togni* Vijaya R. Pattabiraman, Ayodele O. Ogunkoya, Jeffrey W. Bode* Department of Chemistry and Applied Biosciences, Swiss Federal Institute Laboratorium für Organische Chemie, Wolfgang-Pauli-Strasse 10, of Technology, ETH Zürich, CH-8093 Zürich, Switzerland ETH Zürich, 8093 Switzerland Chemoselective ligation reactions that can be performed in aqueous buffers with unprotected peptide/protein segments, ideally between any pair of ami- no acids, are valued reactions for chemical synthesis of proteins. The α- ketoacid–hydroxylamine (KAHA) ligation with 5-oxaproline is apromising method for the preparation of both natural and modified proteins. In this li- gation, aC-terminal peptide α-ketoacidreacts chemoselectively with an N- Since the advent of reagent 1 and 2 aplethora of nucleophiles have been terminal 5-oxaproline peptide to give the target protein with an α- successfully targeted. Among the first functional groups to be trifluoro- homoserine at the ligation site. This ligation works well for the synthesis of methylated, thiols were the most promising ones due to short reaction times proteins in aqueous buffers with unprotected protein segments and produces and ahigh functional group tolerance.1 carbondioxide as the only by-product. When comparing the reactivity of chalcogens towards the reagents very dif- R O O H O N ferent mechanistic behavior is observed. For example, hard oxygen nucleo- H3N Protein Segment 1 N OH N Protein Segment 2 H O O H OH philes such as hydrogen phosphates putatively form acomplex through co- α−Ketoacid 5-oxaproline ordination to the iodonium core followed by reductive elimination to furnish KAHA ligation 2 R the product. Thiols, on the other hand, display distinct characteristicsofa H O N O H3N Protein Segment 1 N N Protein Segment 2 radical mechanism where the S-Cbond formation event is proposed to occur H H through subsequent single electron transfers in aS 2type fashion. As afun- O OH N Synthetic OH Synthetic damental understanding of these mechanisms of action are important in or- cspA protein Synthetic proteins with α-homoserine (Hse, T §) Pup protein der to specifically design new nucleophiles and improve on the reactivity of The synthesis of Prokaryotic ubiquitin-like protein (Pup) and probable cold- 1 and 2,these differences will be discussed and experimental data corrobo- shock proteinA(cspA) using KAHA ligation with 5-oxaproline will be dis- rating either hypothesis presented. cussed along with the scope of the ligation reaction. [1] Kieltsch, I.; Eisenberger, P.; Togni, A. Angew. Chem. Int. Ed. 2007, [1] J. W. Bode, R. M. Fox, K. D. Baucom. Angew. Chem. Int. Ed. 2006, 46,754. 45,1248. [2] Santschi, N.; Geissbühler, P.; Togni, A. J. Fluorine Chem. 2012, 135, [2] V. R. Pattabiraman, A. O. Ogunkoya, J. W. Bode. Angew. Chem. Int. 83. Ed. 2012,DOI: 10.1002/anie.201200907. Organic chemistry CHIMIA 2012, 66, No. 7/8 571 Organic Chemistry Organic Chemistry Organic Chemistry,Talk 362 Organic Chemistry,Talk 363 Synthesis andbiochemical characterization of triphosphates with side Pd-Catalyzed Oxy- andAmino-Alkynylation of Olefins chainscapable of organocatalysisand transitionmetal binding StefanoNicolai,Jérôme Waser Marcel Hollenstein1 LaboratoryofCatalysis andOrganic Synthesis, EPFL, 1 DepartmentofChemistry andBiochemistry, UniversityofBern, 1015 Lausanne,Switzerland Freiestrasse 3, CH-3012 Bern, Switzerland O- and N-containing heterocycles arecommon scaffolds in both natural Nucleoside triphosphates(dNTPs)haveadvanced as aversatile platformfor products andother bioactive compounds.Avaluable strategy for thesynthe- the generation of modifiednucleic acids andaviable alternativetothe tradi- sis of these compounds is basedonthe cyclizationofO-and N-nucleophiles tionalautomated solid-phase synthesis of oligonucleotides [1]. Various onto non-activated olefinscombinedwith afurther C-Cbond forming event. dNTPs embellished with side-chains capable of enamine-basedorganocatal- Despitethe enormous synthetic potential of acetylenes, no methods for the ysis (1-3), activationofLewis basic substratesthroughthe casting of ex- oxy- andaminoalkynylation of olefins hadbeen previouslydescribed. tendedhydrogenbond networks(4and 5), andbinding to transition metals We report herein twocomplementary approaches basedonPdcatalysis to via phosphane lignads(6)weresynthesized [2], [3]. achieve thiskind of transformation.The cyclizationof-alkenyl carboxylic acids1 and N-tosyl amides2 waseffectivelyaccomplishedthrougha Pd(II/IV)-catalyzed processusing the hypervalent iodine reagentTIPS- EBX. The -and -lactams accessed thisway could be then used for the two-step synthesis of pyrrolizidine andindolizidine heterocycles. By con- trast, 2-propargyl tetrahydrofuransand pyrrolidinescould be obtainedin excellent yields anddiastereoselectivitybyPd(0/II)-catalyzed cyclizationof alkenyl alcohols andaminesusing TIPS-protected bromoacetylene. The capacityofthese modifieddNTPs to act as substrates for DNApoly- merases in particular, andtheir compatibility withSELEX in general, was also assessed. [1]Nicolai, S.;Erard, S.;Fernández-González,D;Waser,J.Org. Lett., [1]M.Hocek,M.Fojta, Org.Biomol. Chem. 2008, 6,2233. 2010, 12,384. [2]M.Hollenstein, Chimia, 2011, 65,770-775. [2]Nicolai, S.;Piemontesi, C.;Waser,J.Angew. Chem Int. Ed. 2011, 51, [3]M.Hollenstein, C. J. Leumann, Chem.Eur.J.2012,submitted. 4680. [3]Nicolai, S.;Waser,J.Org. Lett. 2011, 13,6324. OrganicChemistry OrganicChemistry Organic Chemistry,Talk 364 Organic Chemistry,Talk 365 Enantioselective Allylic Amination, Etherification and Thioetherifica- In vitro Studies on the Phenol Coupling and Aromatic Chlorination tion with an uniquely reactive (P,alkene)-Ir Complex: Direct Substitu- Reactions in VancomycinBiosynthesis tion of racemicAllylic Alcohols Patrick C. Schmartz, K. Zerbe, E. Gad, K. Abou-Hadeed, J. A. Robinson* Markus Roggen, Erick M. Carreira University of Zurich, Winterthurerstr. 190, CH-8057 Zurich, Switzerland ETH Zürich, CH-8093 Zürich, Switzerland Glycopeptide antibiotics are promising candidates in the development of Chiral allylic amines, ethers and thioethers are valuable intermediates in or- novel antibacterial compounds that retain activity against Gram-positive ganic synthesis. bacteria. Striking features of this class of natural products are the extensive phenol coupling of alinear peptidic precursor catalyzed by dedicated P450 NH2 enzymes and the regiospecific aromatic chlorination catalyzed by asingle R flavin-dependent halogenase. We have shown in previous substrate specific-
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