Atsuyoshi Ohno

Effect of solvent structure on enantioselectivity of lipase-catalyzed transesterification

Abstract Enantioselectivity in transesterification of a secondary alcohol under lipase-catalysis is largely affected by the solvent used. Two groups of solvents, cyclic and acyclic, show different feature on enantioselectivity.

Asymmetric reduction of ketones by the acetone powder of Geotrichum candidum

Aromatic ketones, β-keto esters, and simple aliphatic ketones were reduced with excellent selectivity to the corresponding (S)-alcohols by using the acetone powder of Geotrichum candidum. This method is superior in reactivity and stereoselectivity to reduction by the whole-cell. The experimental conditions for the reduction system such as ratio of the biocatalyst to the substrate, kinds of coenzymes, alcohol for coenzyme regeneration, and buffer, pH, and reaction temperature were investigated, and stability and preservability of the biocatalyst were also examined. This method is very convenient for the synthesis of optically pure alcohols on a gram scale.

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.

A novel method to synthesize (L)-β-hydroxyl esters by the reduction with bakers' yeast

Abstract β-Keto esters are reduced stereoselectively into the corresponding (L)-β-hydroxyl esters in the presence of ethyl chloroacetate.

Structure of solvent affects enantioselectivity of lipase-catalyzed transesterification

Abstract Lipase-catalyzed transesterification of ( rac )-6-methyl-5-hepten-2-ol (sulcatol) with vinyl acetate has been studied in various solvents and the effect of solvent on the enantioselectivity has been discussed from the viewpoint of molecular shape of the solvent. Alkanes and ethers are selected as solvents. Enantioselectivity of a reaction in a structurally linear solvent is higher than that in the corresponding branched chain solvent. Furthermore, the enantioselectivity decreases specifically with the increase in the ring size of solvent molecule. Thus, lipase recognizes not only the structure of substrate but also that of solvent.

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.

Enantio- and regioselective reduction of α-diketones by baker's yeast

Abstract Although yeast reduction of α-diketones 1 affords a mixture of two α-hydroxy ketones and a vic -diol, the use of methyl vinyl ketone as an enzyme inhibitor prevents the production of the diol. Regioselectivity in the reduction to afford α-hydroxy ketones is improved by thermal pre-treatment of bakers yeast. Thus, 1-phenyl-2-hydroxy-1-propanone 3a is obtained in 80 % yield with >98% e.e.

MICROBIAL DERACEMIZATION OF 1-ARYLETHANOL

Abstract When racemic 1-arylethanol is reacted with Geotrichum candidum IFO 5767 in water, ( R )-1-arylethanol is obtained in high yield with excellent ee. It has been found that ( S )-1-arylethanol is converted into the antipode via oxidation to the corresponding aryl methyl ketone and successive reduction of the ketone to the ( R )-alcohol. Ally alcohol as an additive enhances deracemization.

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.

Asymmetric reduction of α,β-unsaturated ketones with a carbon-carbon double-bond reductase from baker's yeast

Abstract A novel carbon-carbon double-bond reductase was isolated from the cells of bakers yeast. The reduction of α,β-unsaturated ketones catalyzed by this enzyme affords the corresponding saturated ( S )-ketones selectively.