A solution of triphenylphosphine (281 mg, 1.07 mmol) in methylene chloride (5 mL) was cooled to 0° C. and then treated with N-bromosuccinimide (190.4 mg, 1.07 mmol). The reaction mixture was stirred at 0° C. for 30 min and then treated with a solution of 2-[3-chloro-4-(5-methyl-tetrazol-1-yl)-phenyl]-3-cyclohexyl-propionic acid (220 mg, 0.63 mmol) in methylene chloride (4 mL). The clear solution was stirred for 15 min at 0° C. and then allowed to warm to 25° C. where it was stirred for 2 h. The reaction mixture was then treated with 2-aminothiazole (189 mg, 1.89 mmol), and the resulting suspension was stirred for 15 h at 25° C. The reaction mixture was concentrated in vacuo to remove methylene chloride, and the residue was diluted with ethyl acetate (50 mL) and a 1N aqueous hydrochloric acid solution (50 mL). The two layers were separated, and the aqueous layer was extracted with ethyl acetate (1×30 mL). The combined organic extracts were successively washed with a saturated aqueous sodium bicarbonate solution (1×50 mL) and a saturated aqueous sodium chloride solution (1×50 mL), dried over anhydrous magnesium sulfate, filtered, and concentrated in vacuo. Biotage chromatography (FLASH 40S, Silica, 4/1 hexanes/ethyl acetate) afforded 2-[3-chloro-4-(5-methyl-tetrazol-1-yl)-phenyl]-3-cyclohexyl-N-thiazol-2-yl-propionamide (79 mg, 29%) as an amorphous solid: EI-HRMS m/e calcd for C20H23ClN6OS (M+) 430.1343, found 430.1343.
