To a solution of 185 mg of tert-butyl {[3-(3-fluorophenyl)piperidin-4-yl]methyl}[(1R)-1-(1-naphthyl)ethyl]carbamate in 2.00 mL of DMSO was added 18 mg of sodium hydride (55% dispersion) at room temperature, followed by stirring for 10 minutes. 89 mg of methyl 2-chloro-1,3-benzoxazole-5-carboxylate was added thereto, followed by stirring at 100° C. overnight. 55 mg of methyl 2-chloro-1,3-benzoxazole-5-carboxylate was further added thereto, followed by stirring at 100° C. overnight. The reaction mixture was cooled to room temperature, and water was then added thereto, followed by extraction with ethyl acetate. The organic layer was washed with saturated brine, and dried over anhydrous sodium sulfate. After filtration, the filtrate was concentrated under reduced pressure. The residue was purified by silica gel column chromatography (hexane-ethyl acetate and chloroform-methanol) to obtain 33 mg of methyl 2-[4-({(tert-butoxycarbonyl)[(1R)-1-(1-naphthyl)ethyl]amino}methyl)-3-(3-fluorophenyl)piperidin-1-yl]-1,3-benzoxazole-5-carboxylate as a colorless resinous compound. ESI+: 638
