An Efficient Scale-Up Synthesis of BMS-520, a Potent and Selective Isoxazole-Containing S1P1 Receptor Agonist

This article reports an efficient scale-up synthesis of 1-(4-(5-(3-phenyl-4-(trifluoromethyl)isoxazol-5-yl)-1,2,4-oxadiazol-3-yl)benzyl)azetidine-3-carboxylic acid (BMS-520), a potent and selective isoxazole-containing S1P(1) receptor agonist. This process features a highly regioselective cycloaddition leading to a key intermediate, ethyl 3-phenyl-4-(trifluoromethyl)-isoxazole-5-carboxylate, a chemo-selective hydrolysis of its regioisomers, as well as an improved method for 1,2,4-oxadiazole formation, relative to the original synthesis. The improved process was applied to the preparation of multiple batches of BMS-520 for preclinical toxicological studies.