Hydroxynitrile Lyase Discovery, Engineering, and Promiscuity towards Asymmetric Synthesis: Recent Progress

Abstract

Hydroxynitrile lyases (HNLs) primarily catalyze the stereoselective synthesis of cyanohydrins, but some of them also carry out asymmetric nitroaldol synthesis (Henry reaction). By virtue of the importance of asymmetric C−C bond formation, and the wide application of chiral cyanohydrins and β-nitroalcohols, HNLs have gained significance in organic synthesis. Over the years new HNLs have been discovered and their synthetic scope are evaluated. Engineering of HNLs has contributed towards increasing not only the catalytic toolbox but also broad substrate selectivity, stereoselectivity, enzyme stability, and application of the enzymes for different transformations other than the conventional ones. This review describes the recent discoveries of diverse hydroxynitrile lyases (HNLs) and the developments to date since 2016, with respect to their biocatalytic applications in the asymmetric synthesis using both natural and promiscuous reactions.