Yeast‐mediated enantioselective synthesis of chiral R ‐(+)‐ and S ‐(−)‐1‐phenyl‐1‐butanol from prochiral phenyl n ‐propyl ketone in hexane–water biphasic culture

BACKGROUND: The hydrophobic phenyl n ‐propyl ketone was used as a model compound to examine alcohol dehydrogenase activity in Saccharomyces cerevisiae mediated cell culture. Parameters such as pH, hexane‐to‐water volume percentage, and the amount of cofactor Zn 2+ ion for either cell growth or reduction were studied to see their effect on the enantioselectivity toward the product R ‐(+)‐ or S ‐(−)‐1‐phenyl‐1‐butanol. RESULTS: The pH for cell growth in aqueous culture was 7.0, while the pH for reduction in the aqueous portion of the biphasic culture was 5.0. Without Zn 2+ ion the biphasic cultures of middle to high hexane‐to‐water volume percentage exhibited an R ‐(+)‐1‐phenyl‐1‐butanol enantiomeric excess of 53.7% to > 99%. Without Zn 2+ ion the biphasic cultures at low hexane‐to‐water volume percentage possessed an S ‐(−)‐1‐phenyl‐1‐butanol enantiomeric excess of 14.5–46.5%. Exclusively, the enantioselectivity for biphasic cultures containing Zn 2+ ion was an S ‐(−)‐1‐phenyl‐1‐butanol enantiomeric excess of 27.5% to > 99%. Reduction mediated in aqueous culture with varied amount of Zn 2+ ion by the yeast Candida utilis also showed an S ‐(−)‐1‐phenyl‐1‐butanol enantiomeric excess of 79.2–95.4%. CONCLUSION: The enantioselectivity of S. cerevisiae mediated biphasic culture reduction of phenyl n ‐propyl ketone can be manipulated through the cofactor Zn 2+ ion and the hexane volume percentage of the biphasic culture. Copyright © 2008 Society of Chemical Industry