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Stereoselective
Terms modified by Stereoselective Selected AbstractsStereoselective and Enantioselective Syntheses of the Four Stereoisomers of Muscol from (3RS)-MusconeHELVETICA CHIMICA ACTA, Issue 5 2007Yoshifumi Yuasa Abstract Two trans stereoisomers of 3-methylcyclopentadecanol (=muscol), (1R,3R)- 2 and (1S,3S)- 2, were efficiently synthesized from (3RS)-3-methylcyclopentadecanone (=muscone; (3RS)- 1) by a highly stereoselective reduction (Scheme). L-Selectride® (=lithium tri(sec -butyl)borohydride) was used, followed by the enantiomer resolution by lipase QLG (Alcaligenes sp.). The cis stereoisomers of muscol, (1S,3R)- 2 and (1R,3S)- 2, were obtained by the Mitsunobu inversion of (1R,3R)- 2 and (1S,3S)- 2, respectively (Scheme). The absolute configuration of (1R,3R)- 2 was determined by X-ray crystal-structure analysis of its 3-nitrophthalic acid monoester, 2-[(1R,3R)-3-methylcyclopentadecyl hydrogen benzene-1,2-dicarboxylate ((1R,3R)- 3b), and by oxidation of (1R,3R)- 2 to (3R)-muscone. [source] Stereoselective Synthesis of Multifunctionalized 1,2,4-Triazolidines by a Ruthenium Porphyrin-Catalyzed Three-Component Coupling ReactionADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 16-17 2006Ming-Zhong Wang Abstract Multifunctionalized 1,2,4-triazolidines have been synthesized by a ruthenium porphyrin-catalyzed three-component coupling reaction. In a one-pot reaction, ruthenium porphyrins catalyzed the in situ generation of azomethine ylides from ,-diazo esters and imines. Stereoselective 1,3-dipolar cycloaddition reactions of the azomethine ylides with dialkyl azodicarboxylates gave the corresponding 1,2,4-triazolidines in good yields (up to 85,%). Using chiral 8-phenylmenthanol ,-diazo ester as the carbenoid source, chiral 1,2,4-triazolidines have been obtained with good diastereoselectivity (up to 84,% de). Some of the 1,2,4-triazolidines exhibited good cytotoxicity against human nasopharyngeal carcinoma (SUNE1) (IC50=10.4,,M) and human cervical carcinoma (Hela) (IC50=10.7,,M) cell lines. [source] Organocatalytic and Stereoselective [3 + 2] Cycloadditions of Azomethine Imines with ,,,-Unsaturated AldehydesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14 2006Wei Chen Abstract Bipyrazolidin-3-one derivatives are biologically significant compounds and their importance has increased in the past decades. In this paper, the first stereoselective [3 + 2] dipolar cycloadditions of azomethine imines with ,,,-unsaturated aldehydes catalyzed by readily available ,,,-diarylprolinol salts are reported, providing a facile route to the synthesis of various chiral bipyrazolidin-3-one derivatives under mild conditions. The organocatalyst 1,g with strongly electron-withdrawing groups exhibited the best stereoselectivity (exo:endo up to 98:2, for exo product up to 97,% ee), in the combination with trifluoroacetic acid. [source] ChemInform Abstract: Gold-Catalyzed Domino Reactions Consisting of Regio- and Stereoselective 1,2-Alkyl Migration.CHEMINFORM, Issue 43 2010Wenbo Li Abstract A cationic gold(I)-catalyzed domino reaction involving highly regio- and stereoselective 1,2-alkyl migration and heterocyclization or oxygen transfer is developed, in which the product selectivity is controlled by the counteranion of the gold catalyst. [source] ChemInform Abstract: A Solid-Supported Organocatalyst for Highly Stereoselective, Batch, and Continuous-Flow Mannich Reactions.CHEMINFORM, Issue 6 2010Esther Alza Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Stereoselective, Dual-Mode Ruthenium-Catalyzed Ring Expansion of Alkynylcyclopropanols.CHEMINFORM, Issue 19 2009Barry M. Trost Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Highly Regio- and Stereoselective [2 + 3] Cycloadditions of Azomethine Ylides to [70]Fullerene.CHEMINFORM, Issue 15 2008Pavel A. Troshin Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Metal Triflate Catalyzed Highly Regio- and Stereoselective 1,2-Bromoazidation of Alkenes Using NBS and TMSN3 as the Bromine and Azide Sources.CHEMINFORM, Issue 1 2007Saumen Hajra Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Regio- and Stereoselective 1,3-Dipolar Cycloadditions to 6H-1,2-Oxazines Leading to New Heterobicyclic Compounds.CHEMINFORM, Issue 42 2006Elmar Schmidt Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Total Synthesis of Asimicin via Highly Stereoselective [3 + 2] Annulation Reactions of Substituted Allylsilanes.CHEMINFORM, Issue 51 2005Jennifer M. Tinsley Abstract For Abstract see ChemInform Abstract in Full Text. [source] Stereoselective Conjugate Addition of Mixed Organoaluminum Reagents to ,,,-Unsaturated N-Acyloxazolidinones Derived from Carbohydrates.CHEMINFORM, Issue 4 2005Stephan Elzner No abstract is available for this article. [source] New Stereoselective ,-C-Glycosidation by Uncatalyzed 1,4-Addition of Organolithium Reagents to a Glycal-Derived Vinyl Oxirane.CHEMINFORM, Issue 40 2003Valeria Di Bussolo Abstract For Abstract see ChemInform Abstract in Full Text. [source] First Comprehensive Bakkane Approach: Stereoselective and Efficient Dichloroketene-Based Total Syntheses of (.+-.)- and (-)-9-Acetoxyfukinanolide, (.+-.)- and (+)-Bakkenolide A, (-)-Bakkenolides III, B, C, H, L, V, and X, (.+-.)- and (-)-Homogynolide A, (.+-.)-Homogynolide B, and (.+-.)-Palmosalide C.CHEMINFORM, Issue 19 2003Timothy J. Brocksom Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Stereoselective 1,2-Additions of ,-Alkoxymethyllithiums to Aldehydes.CHEMINFORM, Issue 2 2002Robert P. Smyj Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Merging Organocatalysis with an Indium(III)-Mediated Process: A Stereoselective ,-Alkylation of Aldehydes with Allylic AlcoholsCHEMISTRY - A EUROPEAN JOURNAL, Issue 37 2010Montse Guiteras Capdevila Curiosity killed the CAT,ions! The use of stabilized cationic intermediates can be considered as a new frontier in the development of stereoselective reactions. An organocatalytic procedure mediated by the MacMillan imidazolidinone catalyst was coupled with an InBr3 -mediated process for the development of a novel stereoselective allylation reaction of aldehydes. Up to 98,% ee and up to 5:1 d.r. were obtained in the process. [source] Studies on Stereoselective [2+2] Cycloadditions between N,N-Dialkylhydrazones and KetenesCHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2004Eloísa Martín-Zamora Dr. Abstract Staudinger-like cycloadditions between chiral, non-racemic N,N-dialkylhydrazones 1 and functionalized ketenes constitute an efficient methodology for the stereoselective construction of the ,-lactam ring. The potential for fine tuning of the dialkylamino auxiliary structure, the availability of a high-yielding deprotection method for the release of the free azetidinones, and the high thermal and chemical stability of hydrazones as N-dialkylamino imines are highlighted as the key elements for the success of the strategy. This last aspect is of particular importance concerning generality: even hydrazones from easily enolizable aldehydes or from formaldehyde reacted to afford the corresponding cycloadducts with high chemical and stereochemical yields. The syntheses of the ,-amino-,-hydroxyacids (2R,3S)-phenylisoserine (42) and (2R,3S)-norstatin (45) were accomplished as illustrative examples of the synthetic utility of this procedure. A model system for the cycloaddition of g series auxiliaries was studied by ab initio computational methods. The collected results support a two-step mechanism through zwitterionic intermediates, and explain the observed absolute and relative stereochemistry in terms of the preferred outward cycloaddition to the Re face of the hydrazone. La reacción de cicloadición [2+2] de tipo Staudinger entre cetenas funcionalizadas y las hidrazonas quirales 1 constituye un método eficiente para la construcción estereoselectiva del anillo de azetidinona. La modulación de la estructura del grupo dialquilamino empleado como auxiliar, la disponibilidad de un procedimiento eficiente para la desprotección de las , -lactamas libres y la alta estabilidad química y térmica de las hidrazonas como N-dialquilamino iminas son los puntos clave para el éxito de la estrategia. Este último aspecto es de particular importancia por su implicación en la generalidad del método: hidrazonas derivadas de aldehídos fácilmente enolizables o incluso las derivadas de formaldehído reaccionan para dar lugar a los correspondientes cicloaductos con excelentes rendimientos químicos y estereoquímicos. La síntesis de los , -amino- , -hidroxiácidos (2R,3S)-fenilisoserina (42) y (2R,3S)-norestatina (45) se llevaron a cabo como ejemplos ilustrativos del potencial sintético del método. Estudios computacionales ab initio realizados sobre una reacción modelo basada en los auxiliares de la serie g sugieren un mecanismo en dos pasos a través de intermedios zwitteriónicos. Los resultados obtenidos explican la estereoquímica absoluta y relativa, así como el alto grado de inducción observado para estos auxiliares, por la preferencia de la aproximación "outward" de la cetena sobre la cara Re de la hidrazona. [source] Capillary electrophoretic investigation of the enantioselective metabolism of propafenone by human cytochrome P-450 SUPERSOMES: Evidence for atypical kinetics by CYP2D6 and CYP3A4ELECTROPHORESIS, Issue 8 2006Minoo Afshar Abstract An enantioselective CE method was used to identify the ability of CYP450 enzymes and their stereoselectivity in catalyzing the transformation of propafenone (PPF) to 5-hydroxy-propafenone (5OH-PPF) and N -despropyl-propafenone (NOR-PPF). Using in,vitro incubations with single CYP450 enzymes (SUPERSOMES), 5OH-PPF is shown to be selectively produced by CYP2D6 and N -dealkylation is demonstrated to be mediated by CYP2D6, CYP3A4, CYP1A2, and CYP1A1. For the elucidation of kinetic aspects of the metabolism with CYP2D6 and CYP3A4, incubations with individual PPF enantiomers and racemic PPF were investigated. With the exception of the dealkylation in presence of R -PPF only, which can be described by the Michaelis,Menten model, all CYP2D6-induced reactions were found to follow autoactivation kinetics. For CYP3A4, all NOR-PPF enantiomer formation rates as function of PPF enantiomer concentration were determined to follow substrate inhibition kinetics. The formation of NOR-PPF by the different enzymes is stereoselective and is reduced significantly when racemic PPF is incubated. Clearance values obtained for CYP3A4 dealkylation are stereoselective whereas those of CYP2D6 hydroxylation are not. This paper reports the first investigation of the PPF hydroxylation and dealkylation kinetics by the CYP2D6 enzyme and represents the first report in which enantioselective CE data provide the complete in,vitro kinetics of metabolic steps of a drug. [source] Reaction of Carboxylic Acids with Isocyanides: A Mechanistic DFT StudyEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 28 2008Tommaso Marcelli Abstract We present a computational investigation of the reaction between isocyanides and carboxylic acids. Our results indicate that this reaction begins with a stereoselective concerted ,-addition of the acid to the isocyanide, leading exclusively to a Z -acyl imidate. Isomerization to the E isomer and successive rate-limiting 1,3 O,N acyl migration yields an N -formyl imide. The calculated barriers are in good agreement with the experimental reaction conditions. Our results might provide an explanation for the peculiar reactivity observed when this reaction is carried out in a self-assembled capsule. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Stereoselective Syntheses of the Octahydropyrano[2,3- b]pyridine DE Core of 'Upenamide via a Stannous Chloride-Induced Deacetalisation,Cyclisation ProcedureEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 22 2007Cécilia Ménard-Moyon Abstract Two stereoselective syntheses of the octahydropyrano[2,3- b]pyridine DE hemiaminal core of the macrocyclic alkaloid 'upenamide are described. The syntheses proceeded through an efficient stannous chloride-induced deacetalisation,cyclisation procedure. The aza-annulation was stereoselective affording a single stereoisomer having the same relative configuration as in the natural product. The cis ring junction and the cis relationship between 2-H and 8a-H were established by NMR spectroscopy and confirmed by X-ray crystallography. An asymmetric synthesis of the octahydropyrano[2,3- b]pyridine ring system is also disclosed.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Preparation of N -Glycosylhydroxylamines and Their Oxidation to Nitrones for the Enantioselective Synthesis of IsoxazolidinesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 21 2003Stefano Cicchi Abstract N -benzyl- and N -methyl- N -glycosylhydroxylamines 3a,i were conveniently obtained by reaction of sugars with N -substituted hydroxylamines according to a novel procedure. Subsequent oxidation occurred at the alkyl group, selectively affording the corresponding C -phenyl- and C -unsubstituted N -glycosylnitrones. C -phenyl- N -glycosylnitrones 10 and 13 underwent highly stereoselective 1,3-dipolar cycloaddition with dimethyl maleate, with the sugar moiety acting as a chiral auxiliary. Final removal of the glycosyl moiety afforded enantiopure enantiomeric isoxazolidines 17 and ent -17 which are oxa-analogues of proline diester derivatives. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Subsite specificity of trypanosomal cathepsin L-like cysteine proteasesFEBS JOURNAL, Issue 9 2001Probing the S2 pocket with phenylalanine-derived amino acids The S2 subsite of mammalian cysteine proteinases of the papain family is essential for specificity. Among natural amino acids, all these enzymes prefer bulky hydrophobic residues such as phenylalanine at P2. This holds true for their trypanosomal counterparts: cruzain from Trypanosoma cruzi and congopain from T. congolense. A detailed analysis of the S2 specificity of parasitic proteases was performed to gain information that might be of interest for the design of more selective pseudopeptidyl inhibitors. Nonproteogenic phenylalanyl analogs (Xaa) have been introduced into position P2 of fluorogenic substrates dansyl-Xaa-Arg-Ala-Pro-Trp, and their kinetic constants (Km, kcat/Km) have been determined with congopain and cruzain, and related host cathepsins B and L. Trypanosomal cysteine proteases are poorly stereoselective towards d/l -Phe, the inversion of chirality modifying the efficiency of the reaction but not the Km. Congopain binds cyclohexylalanine better than aromatic Phe derivatives. Another characteristic feature of congopain compared to cruzain and cathepsins B and L was that it could accomodate a phenylglycyl residue (kcat/Km = 1300 mm,1·s,1), while lengthening of the side chain by a methylene group only slightly impaired the specificity constant towards trypanosomal cysteine proteases. Mono- and di-halogenation or nitration of Phe did not affect Km for cathepsin L-like enzymes, but the presence of constrained Phe derivatives prevented a correct fitting into the S2 subsite. A model of congopain has been built to study the fit of Phe analogs within the S2 pocket. Phe analogs adopted a positioning within the S2 pocket similar to that of the Tyr of the cruzain/Z-Tyr-Ala-fluoromethylketone complex. However, cyclohexylalanine has an energetically favorable chair-like conformation and can penetrate deeper into the subsite. Fitting of modeled Phe analogs were in good agreement with kinetic parameters. Furthermore, a linear relationship could be established with logP, supporting the suggestion that fitting into the S2 pocket of trypanosomal cysteine proteases depends on the hydrophobicity of Phe analogs. [source] Efficient Regio- and Stereoselective Conversions of Oxiranes and Aziridines into , -(Nitrooxy)-Substituted Alcohols and Amines by Using Bismuth Nitrate,HELVETICA CHIMICA ACTA, Issue 1 2007Biswanath Das Abstract Oxiranes and aziridines efficiently undergo ring opening with bismuth nitrate at room temperature to furnish the corresponding , -(nitrooxy)-substituted alcohols and amines respectively. The conversions are highly regio- and stereoselective and afford the nitrooxy-compounds in excellent yields within a short period of time. [source] The Absolute Configuration of (+)-Ethyl cis -1-Benzyl-3-hydroxypiperidine-4-carboxylate and (+)-4-Ethyl 1-Methyl cis -3-Hydroxypiperidine-1,4-dicarboxylate; a RevisionHELVETICA CHIMICA ACTA, Issue 12 2006Piergiorgio Abstract Discrepancies between chiroptical data from the literature and our determination of the structure of the title compounds (+)- 5 and (+)- 9a were resolved by an unambiguous assignment of their absolute configuration. Accordingly, the dextrorotatory cis -3-hydroxy esters have (3R,4R)- and the laevorotatory enantiomers (3S,4S)-configuration. The final evidences were demonstrated on both enantiomers (+)- and (,)- 5 by biological reduction of 4 by bakers' yeast and stereoselective [RuII(binap)]-catalyzed hydrogenations of 4 (Scheme,2), by the application of the NMR Mosher method on (+)- and (,)- 5 (Scheme,3), as well as by the transformation of (+)- 5 into a common derivative and chiroptical correlation (Scheme,4). [source] A Rapid and Efficient Stereoselective Synthesis of (Z)- and (E)-Allyl Bromides from Baylis,Hillman Adducts Using Bromo(dimethyl)sulfonium Bromide,HELVETICA CHIMICA ACTA, Issue 7 2006Biswanath Das Abstract Treatment of Baylis,Hillman adducts 1 with bromo(dimethyl)sulfonium bromide, Br(Me2)S+Br,, in MeCN was found to stereoselectively afford (Z)- and (E)-allyl bromides 2. The reaction is rapid at room temperature, high-yielding, and highly stereoselective. [source] Practical Stereo- and Regioselective, Copper(I)-Promoted Strecker Synthesis of Sugar-Modified ,,, -Unsaturated IminesHELVETICA CHIMICA ACTA, Issue 3 2006Guobin Zhou Abstract The regio- and stereoselective, Lewis acid catalyzed Strecker reaction between Me3SiCN and different aldimines incorporating a 2,3,4,6-tetrakis- O -pivaloyl- D -glucopyranosyl (Piv4Glc) chiral auxiliary has been worked out. Depending on the conditions used, high yields (up to 95%) and good diastereoselectivities (de >,86%) were achieved under mild conditions (Table,1), especially with CuBr,,,Me2S as catalyst. Our protocol allows the ready preparation of asymmetric ,,, -unsaturated , -amino acids such as (R)-2-amino-4-phenylbut-3-enoic acid (13; Scheme,2) and congeners thereof. [source] ,- and ,-Stannyl Trifluoromethylbutenoates: Regioselective Preparation and Use in Copper(I)-Catalyzed Allylation and Propargylation ReactionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2010Yvan Carcenac Abstract The palladium-free hydrostannylation of ethyl 4,4,4-trifluorobutynoate 1 with tributyltin hydride at room temperature is highly regio- and stereoselective, providing good yields of ,-trifluoromethyl (Z)-,- or (Z)-,-stannylacrylates 2. Vinylstannanes 2 undergo a copper(I)-catalyzed coupling reactions with allylic or propargylic bromides leading selectively to good yields of the corresponding allylated or propargylated products without allylic or allenic transposition. [source] Catalytic 1,2-Dicyanation of Alkynes by Palladium(II) under Aerobic ConditionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009Shigeru Arai Abstract A stereoselective 1,2-dicyanation of various alkynes in the presence of trimethylsilyl cyanide (TMSCN) by palladium(II) catalysis under aerobic conditions is investigated. This reaction includes two cyanation pathways, syn - and anti -cyanopalladation to alkynes that are activated by Pd(II). High syn -selectivity was observed in the reaction using terminal alkynes that have bulky substituents at a propargyl position and aliphatic internal alkynes. Furthermore, a dramatic acceleration was observed with substrates having an N -arenesulfonyl functionality at a propargyl position, this indicates that both sulfoxide and carbon-carbon triple bond act as Lewis bases to Pd(II). [source] Organocatalytic and Stereoselective [3 + 2] Cycloadditions of Azomethine Imines with ,,,-Unsaturated AldehydesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14 2006Wei Chen Abstract Bipyrazolidin-3-one derivatives are biologically significant compounds and their importance has increased in the past decades. In this paper, the first stereoselective [3 + 2] dipolar cycloadditions of azomethine imines with ,,,-unsaturated aldehydes catalyzed by readily available ,,,-diarylprolinol salts are reported, providing a facile route to the synthesis of various chiral bipyrazolidin-3-one derivatives under mild conditions. The organocatalyst 1,g with strongly electron-withdrawing groups exhibited the best stereoselectivity (exo:endo up to 98:2, for exo product up to 97,% ee), in the combination with trifluoroacetic acid. [source] Asymmetric epoxidation of digeranyl by cultured cells of Nicotiana tabacumJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 5 2003Osamu Nakagawa Abstract Asymmetric epoxidation of digeranyl, which is a squalene analog, with cultured cells of Nicotiana tabacum was investigated. Feeding of [8- 3H]-digeranyl into the cultured cells of N. tabacum resulted in the formation of (3S)-2,3-epoxydigeranyl and 6,7-epoxydigeranyl. It was found that the epoxidation of digeranyl with N. tabacum was highly stereoselective. Copyright © 2003 John Wiley & Sons, Ltd. [source] Edited by Wolf-Dieter Fessner and Thorleif Anthonsen Modern biocatalysis: stereoselective and environmentally friendly reactions Wiley-VCH, 2008, 400 pp £110.00/,132.00 978-3-527-32071-4 (hardcover)APPLIED ORGANOMETALLIC CHEMISTRY, Issue 6 2009Gideon Grogan No abstract is available for this article. [source] | ||||||||||||||||||||||||||||