Methanol (2 ml) and a 4 N hydrochloric acid/ethyl acetate solution (2 mL) were added to tert-butyl cis(±)-4-{[(4-chloro-5-ethyl-1H-imidazol-2-yl)carbonyl]amino}-3-methoxypiperidine-1-carboxylate obtained in Example (1g) (60 mg, 0.16 mmol), and the mixture was stirred at room temperature for two hours. Following concentration under reduced pressure, the residue was dissolved in DMF (4 mL). Methyl 2-chloro-1,3-benzooxazole-7-carboxylate (34 mg, 0.16 mmol) (reference: U.S. Pat. No. 6,166,011 A1) and diisopropylethylamine (1 ml) were added, and the mixture was stirred at 80° C. for six hours. Ethyl acetate was added to the reaction solution, and the organic layer was washed with water and dried over anhydrous sodium sulfate. Following concentration under reduced pressure, the residue was recrystallized from an ethyl acetate/hexane solvent to obtain 75 mg of the title compound as crystals. mass spectrum (ESI): m/z 462 (M+H)+.
