Shinzaburo Oka

Stereochemical control in yeast reduction

Abstract A substrate which is subjected to yeast reduction has been modified by iodination or phenylsulfonylation. Both substituents improves chemical and optical yields and control the stereochemical course of the reduction.

Nad(P)+-nad(p)h models. 57 : Stereochemistry in (net) hydride transfer from and to nad(p)+-nad(p)h models: chirality sink

Abstract NAD(P)H/NAD(P) + and related compounds have intrinsic chirality against the axis alone the C 3 –C carbonyl single bond. A model compound which has a stable conformation with respect to this chirality was synthesized and the conformational relationship between the carbonyl dipole and the reacting hydrogen was studied. It has been concluded that there is a relationship between conformations of these groups both in reduction and in oxidation provided the substrate is a neutral species. The result is discussed in relation with the hypothesis proposed previously on the basis of quantum chemical calculations.

Simultaneous microdetermination of capsaicin and its four analogues by using high-performance liquid chromatography and gas chromatography—mass spectrometry

An improved method is described for the simultaneous determination of capsaicin and its analogues at levels from nanograms to micrograms using high-performance liquid chromatography (HPLC) and gas chromatography--mass spectrometry. This method consists of two steps: firstly, purification and determination of total capsaicinoid by HPLC, and secondly, the simultaneous determination of capsaicin and its analogues by mass chromatography (MC) or mass fragmentography (MF). Crude extracts of capsaicinoid were purified with a Zorbax SIL column. Total capsaicinoid was detected at 235 nm and measured automatically by a microcomputer. It was collected, evaporated, trimethylsilylated and subjected to MC or MF. After monitoring the molecular ions of trimethylsilyl derivatives of capsaicinoid and the internal standard, the absolute contents of each analogue were determined by computer. By using this method, capsaicin and all of its analogues can be determined simultaneously at levels from micrograms to nanograms without any interferences from other components.

Stereochemical control in microbial reduction 4. Effect of cultivation conditions on the reduction of β-keto esters by methylotrophic yeasts.

Abstract When β-keto esters are reduced by methanol grown yeast, drastic shift of the enantiomer excess of the products toward D-isomer formation is caused compared with those by glucose grown cells.

NAD(P)+-NAD(P)H model. 52. Reduction of olefins by hantzsch ester on silica gel

Abstract Olefinic double bonds in α,β-unsaturated carbonyl or nitro compounds are reduced chemoselectively by Hantzsch ester on silica gel in excellent yields.

Asymmetric reduction of ketones by glycerol dehydrogenase from geotricum

Abstract Glycerol dehydrogenase from Geotricum was used as a catalyst for asymmetric reduction of ketones. A 2-propanol-NAD + couple was employed to supply NADH.

Reduction by a model of NAD(P)H. 44. Transition metal catalyzed reduction of allylic acetate

Abstract Allylic acetates were reduced regioselectively to alkenes by a model of NAD(P)H via catalytic activation with transition metal complexes.

Reduction by a model of NAD(P)H

Abstract Stereochemistry of the biomimetic reduction of α-keto esters with NAD(P)H-model compounds has been investigated. The model compound with the R-configuration reduces the α-keto esters to the (R)-α-hydroxy esters, whereas (S)-α-hydroxy esters are afforded by the reduction with the S-configurational model compounds. It has been concluded that pro-R and -S hydrogens of the model compounds with R- and S-configuration, respectively, contribute predominantly to the reduction.

Reduction by a model of NAD(P)H: XXIII. Kinetics for the reduction of 2-acylpyridines

Abstract Kinetics for the reduction of 2-acetylpyridine and 2-benzoylpyridine with 1-benzyl-1,4-dihydronicotinamide in acetonitrile has been studied. Isotope effects of the reduction reveal that the transfer of hydrogen nucleus is involved in the rate-determining step. The effect of zinc ion on the reaction rate has been studied quantitatively and the true reacting species have been elucidated.

Cobalt-catalyzed regiospecific conversion of aryl-substituted olefins into alcohols using molecular oxygen and tetrahydroborate. The reaction of oxygen with activated substrates

Abstract Aryl-substituted olefins were converted to benzyl alcohols regioselectively by the use of oxygen and tetrahydroborate in the presence of a catalytic amount of bis (dimethylglyoximato)chloro(pyridine)cobalt(III).