1.75 g (3.26 mmol) of methyl (2S)-2-(benzenesulfonylamino)-3-[4-[1-(benzyloxycarbonyl)-4-piperidyloxy]phenyl]propionate was dissolved in a mixed solvent of 10 ml of methanol and 10 ml of tetrahydrofuran. 6.52 ml (6.52 mmol) of 1 N aqueous sodium hydroxide solution was added to the solution, and they were stirred at 50° C. overnight. The reaction mixture was washed with ether and then made acidic with concentrated hydrochloric acid. After the isolation process with dichloromethane as the extractant in the same manner as that of step 1 in Example 1, an oily residue was obtained, which was dissolved in 60 ml of pyridine. 747 mg (3.61 mmol) of 3-aminobenzamidine dihydrochloride and 750 mg (3.92 mmol) of WSC were added to the solution, and they were stirred at room temperature overnight. The solvent was distilled off, and the residue was purified by the silica gel column chromatography to obtain the title compound.
