关键词： Metabolites  

摘要： A UV-guided fractionation of the AcOEt extract of the fermentation broth of Guignardia sp., an endophytic fungus from the leaves of the tropical tree Spondias mombin, resulted in the identification of the new metabolite (-)-(2S,5Z)-2-(1-methylethyl)-4-oxo-5-(phenylmethylene)-1,3-dioxolane-2-carboxylic acid (1), isolated as NHT4+ salt 1a. The metabolite 1 was designated (-)-(S)-guignardic acid. This first member of a new class of natural compounds contains a dioxolanone moiety formed by fusion of 2-oxo-3-phenylpropanoic acid (phenylpyruvic acid) and 3-methyl-2-oxobutanoic acid (dimethylpyruvic acid), products of the oxidative deamination of phenylalanine and valine. respectively. The structure of 1a was deduced from spectral data (UV. IR, MS. H-1- and C-13-NMR) and confirmed by asymmetric synthesis.

关键词： Functionalization   Trimethylsilyls   Organic compounds   Heterocyclic compounds   Addition reactions  

摘要： [GRAPHICS] We report the diastereoselective addition of a wide range of nucleophiles to chiral pyrazolines to provide facile access to a range of useful densely functionalized building blocks for asymmetric synthesis. Coupled with the asymmetric cycloaddition reaction of Me3SiCHN2 to chiral acrylates, access to these chiral heterocycles is considerably expanded.

关键词： Pd(0)-catalyzed allylic alkylation   Enantioselective synthesis   Reverse-transcriptase   Virus activity   Neplanocin-a   Analogs   Carbovir   (-)-neplanocin-a   (-)-carbovir   1592u89  

摘要： A general and efficient synthesis of carbocyclic and hexenopyranosyl nucleosides has been developed. The strategy combines three key transformations: an asymmetric aldol addition to establish the relative and absolute configuration of the pseudosugar, a ring-closing metathesis to construct the pseudosugar ring, and a Trost-type palladium(0)-mediated substitution to assemble the pseudo-sugar and the aromatic base. Carbovir, abacavir, and their 2'-methyl derivatives gs well as hexenopyranosyl nucleoside analogues have been prepared by this sequence.

关键词： Mixtures   Ethers   Alcohols   Vinyl   Enantioselective synthesis  

摘要： The deracemization of 3-nonyl-3,4-epoxybut-1-ene with Pd(0) in the presence of chiral ligands using p-methoxybenzyl alcohol as a nucleophile proceeds regio- and enantioselectively to form the monoprotected vinylglycidol in 99% ee. This chiral building block was converted in seven steps to (-)-malyngolide, an antibiotic showing significant activity against Mycobacterium smegmatis and Streptococcus pyogenes, An interesting aspect invokes controlling the diastereoselectivity of protonation of an enolate via a distal hydroxyl group.

关键词： Hydrocarbons   Addition reactions   Ethers   Aromatic compounds   Molecular structure  

摘要： [GRAPHICS] The radical addition-cyclization reaction of substrates having two different radical accepters such as acrylate and aldoxime ether moieties was studied. This new free radical mediated Mannichtype reaction proceeded smoothly via a tandem C-C bond-forming process. Furthermore, the diastereoselective tandem reaction provides the novel method for asymmetric synthesis of gamma -butyrolactones and beta -amino acid derivatives.

关键词： 4-氨基-3-羟基-5-环已基戊酸   不对称合成  

摘要： 报道了从 (S) -苹果酸出发合成 (3S,4R) - Statine类似物活化形式的改良方法 .使用 N-保护的苹果酰亚胺后 ,其随后的格氏试剂加成和脱氧还原可分别达到 95%的区域选择性和

关键词： 光学活性   氰醇   不对称合成   对映异构体   手性催化剂   中间体   (S)-α-氰基-3-苯氧基苯甲醇   医药   农药  

摘要： 光学活性氰醇是合成大量医药、农药产品的重要中间体。介绍了用具有光学活性的生物或化学催化剂对前手性底物的不对称化来制备光学活性氰醇的方法,重点对(S)-α-氰基-3-苯氧基苯甲醇的不对称催化作了较为全面的概述,并对不对称合成的特点、机理及发展前景作扼要的介绍。

关键词： 氰醇酶   手性氰醇   不对称合成   制备   手性药物  

摘要： 本文就氰醇酶的来源、反应体系的选择、某些参数的影响及手性氰醇在工业中的应用，特别是在制备手性药物中间体中的应用，作如下综述。

关键词： stereoselective reductions   hydrides   cyclization   asymmetric synthesis   piperidines  

摘要： The asymmetric synthesis of all four stereoisomers of 4-hydroxypipecolic acid (1) from the polyfunctionalized chiral building blocks delta -amino beta -keto esters (S-S,R)-(+)-5 or (R-S,S)-(-)-5 is described. Key steps in the synthesis are the stereoselective reductions of b-phenylpiperidine-2,4-dione (6) and N-sulfinyl delta -amino beta -keto esters 5 to cis 4-hydroxy 2-piperidinone 7 and syn-delta -amino beta -hydroxy ester 9, respectively. The only protecting/deprotecting group chemistry required is related to the oxidation step.

关键词： 2-(1-aminoalkyl)-1,3-oxazoles   asymmetric synthesis   2-oxazolylpiperidines   2-oxazolylpyrrolidines   4,5-dihydroxypipecolinic acid   chiral auxiliaries   heterocycles  

摘要： Asymmetric alpha -alkylation of 2-aminomethyl-4,5-diphenyloxazole was achieved by formation of azomethines 1 and ent-1 with the enantiomers of 2-hydroxypinan-3-one as chiral auxiliaries, reaction with alkylating reagents and final removal of the chiral auxiliary giving rise to optically active 2-(alpha -aminoalkyl)oxazoles 3, ent-3, 6 and 9. If alpha,omega -dihaloalkanes were used the resulting alkylation products could be further cyclized by intramolecular alkylation of the amino group to afford optically active 2-oxazolyl-N-heterocycles 4, ent-4, 7 and 10. The latter could be used for the total synthesis of naturally occurring 4,5-dihydroxypipecolinic acid 13.