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-pyridinecarboxaldehyde in >65% yield. Hydroxynitrile lyases (HNLs) from cassava and almond were used in commercially available cross-linked 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.