To an ethanol (350 mL) solution of the compound (55.7 g) obtained in Example 2, 20% palladium hydroxide-carbon (13.6 g) was added under an argon atmosphere. The reaction mixture was stirred under a hydrogen atmosphere at 60° C. for 6 hours. The reaction mixture was cooled to room temperature and then filtered through Celite. The filtrate was concentrated under reduced pressure. The residue was purified by silica gel chromatography (ethyl acetate:10%-saturated aqueous ammonia-methanol=1:0→8:2) to obtain the title compound (28.5 g) having the following physical properties.
