Mass transfer limitation as a tool to enhance the enantiomeric excess in the enzymatic synthesis of chiral cyanohydrins

The enantioselective synthesis of cyanohydrins catalyzed by R-hydroxynitril e lyase in an aqueous-organic liquid two-phase system using, mass transfer limitation to enhance enantiomeric excess at 5 degreesC and pH 5.5 is descr ibed. Benzaldehyde, a good substrate, and cinnamaldehyde, a notoriously dif ficult substrate, were used as model substrates and compared in order to es tablish the mass transfer limitation concept in a two-liquid phase system, where the non-enzymatic-racemic reaction competes. Enzyme concentration and phase volume ratio between organic and buffer phase were geared to one ano ther to enhance the enantiomeric excess for each substrate. In both cases, after optimization, excellent chemical conversion (> 99% on a 60 mmol scale ), high throughput and high enantiomeric excess (benzaldehyde > 99% and cin namaldehyde > 96%) were achieved. (C) 2001 Elsevier Science B.V. All rights reserved.