A solution of 2-(3-chloro-4-methylsulfonyl-phenyl)-3-(4-oxo-cyclohexyl)-propionic acid (267 mg, 0.75 mmol) in methylene chloride (10 mL) was treated with N,N-dimethylformamide (3 drops) and then cooled to 0° C. The reaction mixture was then treated with a 2.0M solution of oxalyl chloride in methylene chloride (0.45 mL, 0.90 mmol). The reaction mixture was stirred at 25° C. for 30 min and then concentrated in vacuo to remove solvents and excess oxalyl chloride. The resulting residue was re-dissolved in dry tetrahydrofuran (10 mL) and was treated dropwise with a solution of 2-aminopyrazine (143 mg, 1.50 mmol) in tetrahydrofuran (10 mL) and pyridine (0.30 mL, 3.75 mmol). The resulting reaction mixture was stirred at 25° C. for 2 h. The reaction mixture was then diluted with a 1N aqueous citric acid solution (25 mL) and concentrated to remove tetrahydrofuran. The remaining aqueous residue was then extracted with a 3/2 solution of chloroform/methanol (2×25 mL). The combined organic extracts were dried over sodium sulfate, filtered, and concentrated in vacuo. Biotage chromatography (FLASH 40S, Silica, 3/2 hexanes/ethyl acetate) afforded 2-(3-chloro-4-methanesulfonyl-phenyl)-3-(4-oxo-cyclohexyl)-N-pyrazin-2-yl-propionamide (266 mg, 81%) as an off-white foam: EI-HRMS m/e calcd for C20H22ClN3O4S (M+H)+ 436.1093. found 436.1099.
