25 ml of 4 N solution of hydrogen chloride in dioxane and 12.5 ml of dioxane were added to 2.54 g (4.34 mmol) of 3-[(2S)-3-[4-[1-(benzyloxycarbonyl)-4-piperidyloxy]phenyl]-2-(t-butoxycarbonylamino)propoxy]benzonitrile. After stirring at room temperature for 24 hours, the solvent was evaporated under reduced pressure, and the residue was dissolved in 40 ml of dimethylformamide. 1.77 ml (13.0 mmol) of diisopropylethylamine and 1.97 g (6.51 mmol) of 4-iodobenzenesulfonyl chloride were added to the solution at 0° C. 30 minutes after, the temperature was elevated to room temperature, and the reaction mixture was stirred for 19 hours. After the treatment with ethyl acetate as the extractant in an ordinary manner, the crude product was obtained. The crude product was purified by the silica gel column chromatography to obtain the title compound.
