Stereoselective reduction of 2-butenolides to chiral butanolides by reductases from cultured cells of Glycine max

The stereoselective reduction of 2-butenolides by two reductases, p51 and p83, from cultured plant cells of Glycine max was investigated. The reduction of 2-methyl-2-butenolide by p51 reductase produced (R)-2-methylbutanolide, whereas the reduction by p83 reductase gave (S)-2-methylbutanolide. Both reductases reduced 3-methyl-2-butenolide to (R)-3-methylbutanolide. The reduction of 2,3-dimethyl-2-butenolide by p51 reductase gave (2R,3R)-2,3-dimethylbutanolide, whereas the reduction by p83 reductase produced (2S,3R)-2,3-dimethylbutanolide. The reduction of 4-alkyl-2-butenolides with these reductases was accompanied by resolution of chiral centers affording (R)-4-alkylbutanolides.     

Stereospecific substitution of enantiomerically pure 1-(2-pyridinyl)ethyl methanesulfonate with beta-dicarbony compounds

The alkylation of the sodium salt of the malonic acid diester with (R)-1-(2-pyridinyl)ethyl methanesulfonate (2) gave the dimethyl (R)-[1-(2-pyridinyl)ethyl]malonate (3a), stereospecifically. The alkylation reaction of methyl acetoacetate gave the methyl (2'S,2R/2S)-3-oxo-2-[1-(2-pyridinyl)ethyl]butanoate (3d) along with the methyl (S)-3-[1-(2-pyridinyl)ethoxy]-2-butenoate (4d). The acid hydrolysis and decarboxylation of 3d under acidic conditions gave (R)-4-(2-pyridinyl)pentan-2-one (6), and the alkylation of methyl (R)-[1-(2-pyridinyl)ethyl]acetoacetate with benzyl bromide gave a mixture of C-benzylated and O-benzylated products 7 and 8.     

Characterization of polymer sub-surface using slow positron beam

A new pulsed mono-energetic slow positron beam as well as the conventional positron annihilation lifetime spectroscopy (PALS) have been applied to study the sub-surface and the bulk of epoxy polymer. Significant changes of o-Ps parameters were found at a short distance from the surface. The lifetime of o-Ps was observed to decrease with increasing the positron implantation depth, while its intensity increased. The temperature effect on o-Ps parameters at sub-surface was also investigated. The glass transition temperature for the sub-surface was lower than that for the bulk. Furthermore, the thermal expansion coefficient of the sub-surface was found smaller than that of the bulk.     

Total synthesis of (-)-kaitocephalin

[reaction: see text] Total synthesis of the potent AMPA/KA receptor antagonist (-)-kaitocephalin (1) and its three diastereomers has been accomplished. The synthesis features strictly substrate-controlled operations to alpha-formylglutamate 3 starting with alpha-hydroxymethylglutamate 4. The requisite 2R,3S,7R-stereocenters were efficiently constructed by manipulation of stereoselective reactions: dihydroxylation of 7 followed by azide substitution of the corresponding thionocarbonate 10 and Cu-mediated allylation of an acyliminium ion 21. All of the protecting groups in 26 were removed simultaneously by AlCl3/Me2S to give 1.     

Liquid-liquid extraction of transition and alkali metal cations by a new calixarene: Diphenylphosphino calix[4]arene methyl ether

The liquid-liquid extraction of various metal ions by a diphenylphosphino calix[4]arene (1) using picrate counter ion has been studied and compared with those ofp-tert-butyl-calix[4]arene methyl ether (2) and triphenylphosphine (3). The calixarene 1 shows strong binding ability to almost all metal cations examined, but calixarene 2 shows little ability to extract any of them. Based on the continuous variation method, calixarene 1 formed 1: 2 complexes with copper(II) ion.     

New methods and reagents in organic synthesis. 49. A highly efficient stereoselective synthesis of L-daunosamine through direct C-acylation using diphenyl phosphorazidate (DPPA)

L-Daunosamine, the carbohydrate component of a group of important anticancer anthracycline antibiotics, has been efficiently prepared from L-lactic acid in a completely stereoselective manner through direct C-acylation using diphenyl phosphorazidate (DPPA).     

Photochemical reactions of polymers containing thiocyanatoacetyl groups and dyeing the resulting polymer films

Poly(styrene-co-4-thiocyanatoacetylstyrene) and poly(4-acetylstyrene-co-4-thiocyanatoacetyl-styrene) were prepared and their photochemical reactions were studied in the solid state. It was found that the thiocyanatoacetyl groups were easily rearranged with the corresponding isothiocyanatoacetyl groups by ultraviolet (UV) irradiation and that the resulting isothiocyanatoacetyl groups underwent intramolecular cyclization when treated with triethylamine or ammonia to yield oxazole-2-thione moieties. The irradiated polymer films could be dyed selectively with cationic dyes in an appropriate dye bath because of the formation of anionic species by keto-enol tautomerization of oxazole-2-thione moieties in an alkaline state.     

Proposed structure of the cyclic peptide dolastatin 3, a powerful cell growth inhibitor,should be revised!

The cyclic peptide proposed for the structure of the powerful cell growth inhibitory dolastatin 3, its diastereomers, and their isomers on the reverse order have been synthesized by the use of diphenyl phosphorazidate(DPPA) and diethyl phosphorocyanidate(DEPC). Their physicochemical and biological properties have shown that the proposed structure is untenable.