Synthesis of Chloramphenicol via an Enzymatic Enantioselective Hydrolysis

Abstract
An efficient method for the preparation of the antibiotic chloramphenicol [(+)-4] is described. Methyl (±)-threo-N-dichloroacetyl-ß-(4-nitrophenyl)serinate [(±)-threo-2], readily obtainable on a preparative laboratory scale, was enantioselectively hydrolyzed by Subtilisin. This enzymatic kinetic resolution gave the corresponding (2S,3R)-acid 3 and the unhydrolyzed (2R,2S)-ester (-)-threo-2 in high yield and high optical purity. Reduction of the (2S,3R)-acid 3 by borane-methyl sulfide complex gave chloramphenicol [(+)-4]. Reduction of the (2R,3S)-ester (-)-threo-2 by lithium aluminum hydride gave the enantiomer (-)-4 chloramphenicol.