A suspension of 3-cyclopentyl-2(R)-(4-methanesulfonyl-phenyl)-N-thiazol-2-yl-propionamide (1.0 g, 2.64 mmol) and N-bromosuccinimide (470 mg, 2.64 mmol) in carbon tetrachloride (5 mL) at 25° C. was treated with benzoyl peroxide (32 mg, 0.132 mmol). The resulting reaction mixture was heated to 90° C. where it was stirred at this temperature overnight. The reaction mixture was allowed to cool to 25° C. and then concentrated in vacuo. The resulting residue was dissolved in ethyl acetate (60 mL). The organic phase was then washed with water (1×100 mL) and a saturated aqueous sodium chloride solution (1×100), dried over anhydrous magnesium sulfate, filtered, and concentrated in vacuo. Biotage chromatography (FLASH 40M, Silica, 2/1 to 1/1 hexanes/ethyl acetate) afforded N-(5-bromo-thiazol-2-yl)-3-cyclopentyl-2(R)-(4-methanesulfonyl-phenyl)-propionamide (546 mg, 45%) as an amorphous solid: EI-HRMS m/e calcd for C18H21BrN2O3S2 (M+) 456.1077, found 456.1077.
