Reduction of a variety of 2-alkyl-3-oxobutanoates with bakers’ yeast yields the corresponding L-(3S)-hydroxy esters with exclusive enantioselectivity, while the diastereoselectivity, syn/anti ratio, varies depending on the structure of the alkoxyl moiety. In order to elucidate the mechanism for this stereochemicalcontrol, oxidoreductases that reduce 2-alkyl-3-oxobutanoate have been isolated from the
Bakers’ yeast reduces esters of 2-alkyl-3-oxobutanoic acid (CH3COCHRCO2R′; R=methyl, ethyl, propyl, propargyl, and allyl) into the corresponding (S)-hydroxy esters with exclusive stereoselectivity, while the configuration at the 2-position of the hydroxy esters is either S (anti) or R (syn) depending on the structure of the alkoxyl group in the carboalkoxyl moiety of the ester. Oftenly, the stereoselectivity