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Four stereoisomers of PRDAs 1∼4 , a novel aspartate analogue incorporating a pyrrolidine ring, were synthesized in an enantiomerically pure form starting from a chiral synthon, 5-amino-5,6-dihydropyrone. Electrophysiological experiments of 1∼4 in newborn rat spinal cords showed a variety of depolarizing activities. The conformational studies of PRDAs and their activity profile suggested that the gauche and the anti conformers about two carboxylic acid groups of Asp could be active forms to NMDA and non-NMDA receptors, respectively

Olefination of dialkyl squarates 1–5 with several ylides 6 and phosphonates 7 gave the corresponding alkylidene products 8–12 . In the case of Horner-Emmons reactions, stereoselective formation of Z -alkylidene products was observed. An acid-catalyzed hydrolysis of 8–12 gave squarylacetic acid esters 13 .

A series of optically active α, α-disubstituted α-amino acids have been synthesized starting with an achiral or a racemic 2-hydroxy ketone. The key transformation to the present synthesis is an intramolecular version of Strecker synthesis. An α-keto ester having a chiral amino acid as the ester group afforded cyclic amino nitrile, in a highly stereoselective manner, in which the amino group and the chirality were diastereoselectively transplanted into the internal ketone group via an imine-enamine equilibrium of the cyclic ketimine intermediate. Oxidation of the amino group followed by removal of the resulting imino group and hydrolysis of the nitrile group afforded α-hydroxymethyl α-amino acid. The use of L-amino acid as the chirality transferring group gave R enantiomer, and its S enantiomer was obtained when D-amino acid was employed. The syntheses of optically active α-substituted serines, α-methylthreonines, and 1-amino-2-hydroxycycloalkanecarboxylic acids are described.

A variety of chiral β-hydroxy-α-amino acids and derivatives thereof can be synthesized enantioselectively using the aldol reaction of an aldehyde, the glycinate 1 and the cinchonidine-derived catalyst 2, as indicated in Schemes 1 and 2 and Table 1.

A novel chiral Rh(II) catalyst (1) is introduced for the [2 + 1]-cycloaddition of ethyl diazoacetate to terminal acetylenes and olefins with high enantioselectivity. The catalyst 1 consists of one acetate bridging group and three mono-N-triflyldiphenylimidazoline-2-one bidentate ligands (DPTI) spanning the Rh(II)-Rh(II) metallic center in a structure that was determined by single-crystal X-ray diffraction analysis. A rational mechanism is advanced that provides a straightforward explanation for the enantioselectivity and absolute stereochemical course of the [2 + 1]-cycloaddition reactions. A key element in this explanation is the cleavage of one of the Rh-O bonds of the bridging acetate group in the intermediate Rh-carbene complex to form a new pentacoordinate Rh carbene complex (formally 1.5 valent Rh) that can undergo [2 + 2]-cycloaddition with the C-C pi-bond of the acetylenic or olefinic substrate. Reductive elimination of the resulting adduct affords the cyclopropene or cyclopropane product. The C2-symmetry of the two DPTI ligands orthogonal to the bridging acetate also contributes to the high observed enantioselectivity and mechanistic clarity. The catalyst 1, which functions effectively at 0.5 mol %, can be recovered efficiently for reuse. Its ready availability, robustness, and effectiveness suggest it as a useful addition to the list of practical chiral Rh(II) catalysts for synthesis.

A novel polyamine toxin, named MG30, was isolated from the venom of the spider, Macrothele gigas, and its structure was elucidated by two-dimensional NMR and mass analysis. In addition, the enantioselective synthesis of MG30 was achieved to assign its absolute stereochemistry.