STEREOCHEMICAL CONTROL OF MICROBIAL REDUCTION .17. A METHOD FOR CONTROLLING THE ENANTIOSELECTIVITY OF REDUCTIONS WITH BAKERS-YEAST

The stereoselectivity of the bakers' yeast catalyzed reduction of beta-keto esters to optically active beta-hydroxy esters can be controlled by the introduction of a third reagent. To gain insight into the mechanism of this enzymatic reduction, beta-hydroxy ester oxidoreductases were isolated from the cells of raw bakers' yeast. Four dominant competing enzymes were isolated, purified, and characterized. Among these, two reduce beta-keto esters stereo-specifically to the corresponding D-beta-hydroxy esters. The other two afford the L-hydroxy esters. The rates of enzymatic reduction were determined in the presence and absence of the additives.