Discovery and characterization of a new hydroxynitrile lyase

Abstract

A robust and practical method has been developed for the synthesis of florfenicol (1) starting from commercial available 4-(methylsulfonyl) benzoic acid. The key step in this synthesis was the Ru-chloramphenicol base catalyzed asymmetric transfer hydrogenation of N-Boc α-amino-β-ketoester 5 through a dynamic kinetic resolution, which afforded the key chiral building block, anti-(2S,3S)-α-Boc-amino-β-hydroxyl ester 4, with high diastereoselectivity (92% de) and enantioselectivity (78% ee). The synthesis of a series of novel chloramphenicol base ligands L1–L10 is also included. This protocol could also be used for the asymmetric synthesis of fully synthetic analogs of florfenicol.