Baliospermum montanum hydroxynitrile lyase catalyzed synthesis of chiral cyanohydrins in a biphasic solvent

Abstract

This study presents asymmetric synthesis of cyanohydrins in aqueous–organic biphasic system using crude Baliospermum montanum hydroxynitrile lyase (BmHNL). The effect of various biocatalytic parameters e.g. different organic solvents, ratio of organic solvents, substrate concentration (benzaldehyde and HCN), pH, and temperature were studied to achieve highest % conversion and enantiomeric excess of (S)-mandelonitrile. Among the organic solvents i.e. hexane, toluene, acetonitrile, tert-butyl methyl ether (TBME), di-isopropyl ether (DIPE) and n-butyl acetate studied, 10% n-butyl acetate showed best results. Optimal results were also found with 0.8 mM benzaldehyde, 10 min reaction time, pH 4.2 and substrate to KCN ratio of 1:125. Under optimal biocatalytic conditions more than a dozen of different aromatic aldehydes were converted into corresponding chiral (S)-cyanohydrins. This method also reports the synthesis of eight chiral (S)-cyanohydrins for the first time, not synthesized by any (S)-selective HNL earlier.