Enantioselective Enzymatic Hydrolysis of rac-Mandelonitrile to R-Mandelamide by Nitrile Hydratase Immobilized on Poly(vinyl alcohol)/Chitosan–Glutaraldehyde Support

Abstract

Nitriles, amides and carboxylic acids have varied applications in active pharmaceutical intermediate (API), drug and chemical industry, and particularly in the synthesis of pure enantiomers of chiral compounds. The chemical hydrolysis of nitrile compounds is well studied, but it necessitates harsh conditions along with the protection of sensitive functional groups, which on deprotection leads to generation of a large amount of byproducts. Immobilization of nitrile hydratase using a novel support reduces the cost and allows green processes. In this work, enantioselective hydrolysis of rac-mandelonitrile was studied using poly(vinyl alcohol) (PVA)/chitosan–glutaraldehyde cross-linked Rhodococcus rhodochrous ATCC BAA-870 nitrile hydratase (NHase). Immobilized NHase converted rac-mandelonitrile to (R)-amide by dynamic kinetic resolution with enantiomeric excess (ee) up to 81%. The temperature of 40 °C and pH 8 were found to be optimum for the enantioselective nitrile hydrolysis. In the presence of various cosolvents, immobilized NHase showed higher retention of activity in methanol compared to other cosolvents. The kinetic constants for free and immobilized enzyme were obtained from the Lineweaver–Burk plot. The immobilized NHase was found to be reusable up to nine successive batch reactions.