Asymmetric synthesis of cyanohydrin derived from pyridine aldehyde with cross-linked aggregates of hydroxynitrile lyases

Enantiocomplementary R- and S-cyanohydrins with > 93% ee were synthesized through the hydrocyanation of 3-pyridine-carboxaldehyde in > 65% yield. Hydroxynitrile lyases (HNLs) from cassava and almond were used in commercially available crosslinked enzyme aggregate (CLEA) forms to catalyze the reactions and produce material with optical purities significantly greater than has been reported previously. The use of a dichloromethane reaction system with enzyme aggregates and free hydrogen cyanide was crucial in improving cyanohydrin stereoselectivity through minimizing background racemic cyanide addition and enzyme-catalyzed racemization of the product. (c) 2007 Elsevier Ltd. All rights reserved.