A solution of triphenylphosphine (3.35 g, 12.79 mmol) in methylene chloride (19 mL) was cooled to 0° C. and then slowly treated with N-bromosuccinimide (2.28 g, 12.79 mmol) in small portions. The reaction mixture was stirred at 0° C. for 30 min, and during this time period, the color of the reaction mixture changed from light yellow to a darker yellow then to a purple color. The cooled purple reaction mixture was then treated with the (2R)-3-cyclopentyl-2-(4-methanesulfonylphenyl)propionic acid (2.23 g, 7.52 mmol). The resulting reaction mixture was then allowed to warm to 25° C. over 45 min, at which time, the reaction mixture was then treated with 2-aminothiazole (1.88 g, 18.81 mmol). The resulting reaction mixture was stirred at 25° C. for 12 h. The reaction mixture was then concentrated in vacuo to remove methylene chloride. The remaining black residue was diluted with ethyl acetate (300 mL) and then washed well with a 10% aqueous hydrochloric acid solution (2×100 mL), a 5% aqueous sodium bicarbonate solution (3×100 mL), and a saturated aqueous sodium chloride solution (1×200 mL). The organic layer was then dried over sodium sulfate, filtered, and concentrated in vacuo. Flash chromatography (Merck Silica gel 60, 70-230 mesh, 9/1, 3/1, and then 11/9 hexanes/ethyl acetate) afforded (2R)-3-cyclopentyl-2-(4-methanesulfonylphenyl)-N-thiazol-2-yl-propionamide (2.10 g, 74%) as a white foam: mp 78-80° C. (foam to gel); [α]23589=−70.40° (c=0.027, chloroform); EI-HRMS m/e calcd for C18H22N2O3S2 (M+) 378.1072, found 378.1081.
