Stereochemical Control of Yeast Reduction of a-Keto Esters in an Organic Solvent (BIOORGANIC CHEMISTRY-Bioorganic Reaction Theory)

Abstract

Yeast reduction of a-keto esters in water afforded the corresponding (R)-hydroxy ester while the antipodes were obtained in the reduction in benzene. To elucidate the mechanism for stereochemical control of yeast reduction, seven enzymes responsible for the reduction have been isolated from bakers' yeast and kinetic parameters for enzymatic reductions have been measured. It was found that the (R)- producing enzymes have smaller Kms than those of the (S)-producing enzymes. When the reaction is run in benzene, however, the produced a-hydroxy ester does not undergo further decomposition. The inhibition of enzymatic decomposition in an organic solvent is also accounted for by low concentration of a-hydroxy ester in aqueous phase surrounding the bakers' yeast.