To a solution of the compound 9 in methanol (2 mL), concentrated hydrochloric acid (2 mL) was added. The reaction mixture was stirred at 80° C. for 5 hours. The reaction mixture was added by an aqueous 5N sodium hydroxide solution and then extracted with dichloromethane. The extract was washed with saturated brine, dried over anhydrous sodium sulfate and then concentrated. The obtained residue was purified by silica gel column chromatography (dichloromethane:methanol:28% ammonia water=80:10:1→80:20:4) to obtain the title compound (21 mg) having the following physical properties.
