Enzymatic Synthesis of Optically Pure (R)-(-)-Mandelic Acid and Other 2-Hydroxycarboxylic Acids: Screening for the Enzyme, and Its Purification, Characterization and Use

Abstract

An enzyme that reduces benzoylformate with NADH to form (R)-mandelate was extracted from cells of Streptococcus faecalis IFO 12964 and purified to more than 95% purity as evidenced by gel electrophoresis. Physicochemical and enzymic properties were studied. From the substrate specificity, we concluded that the enzyme was a kind of (R)-2-hydroxyisocaproate dehydrogenase. Optically pure (R)-(-)-mandelic acid was prepared with the enzyme, NADH, and alcohol, formate or glucose dehydrogenase in 84-93% yield. Five (R)-2-hydroxyalkanoic acids (C₄-C₆) or their Ba salts, (R)-(+)-3-phenyllactic acid and (S)-(-)-3-chlorolactic acid were also prepared with the enzyme.