STEREOCHEMICAL CONTROL IN MICROBIAL REDUCTION .21. EFFECT OF ORGANIC-SOLVENTS ON REDUCTION OF ALPHA-KETO ESTERS MEDIATED BY BAKERS-YEAST

Reduction of alpha-keto esters mediated by bakers' yeast takes place in an organic solvent without immobilization of the microbe. Several factors such as water content, pH of the solution, amount of bakers' yeast, and the property of the organic solvent affect to enantioselectivity of the reduction. In benzene, stereochemistry of the reduction shifts markedly toward preferential production of the (R)-alpha-hydroxy ester. The stereochemical consequence of the present reaction is accounted for by two factors; 1) the inhibition of enzymatic decomposition of the produced (R)-alpha-hydroxy ester in benzene and 2) the enhancement of relative activities of dehydrogenases or reductases in producing the (R)-alpha-hydroxy ester under dilute concentrations of the substrate at the vicinity of enzymes.