The synthesis of optically active α-hydroxy β-methyl esters V by means of microbiological reduction of the corresponding α-keto β-methyl esters IV was carried out. Methyl 3-phenyl-2-oxobutyrate 3 was found to be reduced by a variety of yeasts to the α-hydroxy β-methyl esters (7b and 8a) with (2R, 3S)-and (2R, 3R)-configurations, respectively, and by carrying out screening experiments, yeasts which give products with high optical purity were actually found.
