Regioselective Epoxide Ring Opening for the Stereospecific Scale-Up Synthesis of BMS-960, A Potent and Selective Isoxazole-Containing S1P1 Receptor Agonist

This article presents a stereospecific scale-up synthesis of (S)-1-((S)-2-hydroxy-2-(4-(5-(3-phenyl-4-(trifluoromethyl)­isoxazol-5-yl)-1,2,4-oxadiazol-3-yl)­phenyl)­ethyl)­piperidine-3-carboxylic acid (BMS-960), a potent and selective isoxazole-containing S1P1 receptor agonist. The process highlights an enzymatic reduction of α-bromoketone toward the preparation of (S)-bromo alcohol, a key precursor of (S)-4-(oxiran-2-yl)­benzonitrile. A regioselective and stereospecific epoxide ring-opening reaction was also optimized along with improvements to 1,2,4-oxadiazole formation, hydrolysis, and crystallization. The improved process was utilized to synthesize batches of BMS-960 for Ames testing and other toxicological studies.