HOW CAN A YEAST CATALYZE ENANTIOSELECTIVE PROTONATION

In the enantioselective hydrolysis of enol esters with Pichia farinosa IAM 4682 to give alpha-chiral ketones, the final enantioselective protonation was found to be promoted by a factor differed from the enzyme catalyzing simple hydrolysis. The crude cell-free extracts from P. farinosa was subjected to ultracentrifugation. Although the supernatant fraction could hydrolyze 1-acetoxy-2-benzylcyclohexene (1), the resulting 2-benzylcyclohexanone (2) was a racemate. On the other hand, the precipitate could not hydrolyze 1. However, on mixing of both fractions the suspension recovered again an enantioselective ability effectively to afford optically active (R)-2. The same phenomena were observed in the hydrolysis using commercially available lipases and an esterase. These results indicate that enantioselectivity-promoting factor should be involved in the precipitate.