To a solution of N-[(3R,4R)-3-(3,4-dichlorophenyl)-1-(piperidin-4-ylcarbonyl)piperidin-4-yl]-N-methyl-3,5-bis(trifluoromethyl)benzamide monohydrochloride (0.35 g) obtained in Example 89 and triethylamine (0.24 mL) in acetonitrile (10 mL) was added acetyl chloride (0.080 mL) at 0° C., and the mixture was stirred at room temperature for 14 hr. The reaction mixture was poured into water, the mixture was made basic with 2N aqueous sodium hydroxide solution, and the resultant product was extracted with ethyl acetate. The organic layer was washed with aqueous sodium hydrogen carbonate solution and brine and dried, and the solvent was evaporated under reduced pressure. The obtained residue was purified by silica gel column chromatography (NH Chromatorex) (solvent gradient; 75→100% ethyl acetate/hexane) to give the title compound (0.25 g, 71%) as a white crystal powder.
