750 mg (3.60 mmol) of the compound obtained in step 1 described above was dissolved in 8 ml of benzene. 0.02 ml of pyridine was added to the obtained solution, and 3.5 ml (48.2 mmol) of thionyl chloride was added to the obtained mixture under cooling with ice. After stirring the reaction mixture at 0° C. for 1 hour and then at room temperature for 2 hours, the solvent was evaporated under reduced pressure. 10 ml of tetrahydrofuran was added to the residue. 2.5 ml (18 mmol) of triethylamine and 805 mg (4.32 mmol) of t-butyl piperazinecarboxylate were added to reaction mixture under cooling with ice. The temperature of the mixture was slowly elevated to room temperature, and it was stirred overnight. The solvent was evaporated under reduced pressure. Dichloromethane was added to the residue. After washing with water and saturated aqueous sodium chloride solution, the organic layer was dried over anhydrous magnesium sulfate. The solvent was evaporated under reduce pressure, and the residue was purified by the basic silica gel chromatography (hexane: dichloromethane=9:1) to obtain the title compound.
