A highly stable whole-cell biocatalyst for the enantioselective synthesis of optically active alpha-hydroxy acids

BACKGROUND: Biocatalysts have gained increasing attention because of their inherent advantages over chemical catalysts. However,the poor operational stability has always prevented their broad application. In this study, (R)-mandelic acid was chosen as a model compound of alpha-hydroxy acids. The objective was to obtain a new biocatalyst with desired operational stability for the preparation of (R)-mandelic acid as well as other optically pure alpha-hydroxy acids of pharmaceutical importance. RESULTS: Using a two-step screening strategy, Saccharomyces ellipsoideus GIM2.105 was selected as an effective biocatalyst with high enantioselectivity and remarkable operational stability. After 20 cycles of reuse, whole cells of S. ellipsoideus GIM2.105 maintained its activity, and no obvious decrease in conversion or enantiomeric excess (ee) was observed. Furthermore, effects of various reaction parameters, including pH, temperature, co-substrate (type, concentration), substrate concentration and reaction time, on the bioreduction were studied. Under optimal conditions, (R)-mandelic acid and four substituted aromatic (R)-alpha-hydroxy acids were prepared in high ee (95 -> 99%) and good conversion (>90%). CONCLUSION: The high enantioselectivity, remarkable operational stability and mild reaction conditions showed S. ellipsoideus GIM2.105 to be an economical biocatalyst with great industrial application potential for the production of optically active alpha-hydroxy acids. (C) 2009 Society of Chemical Industry