Compound 1 (200 mg) was dissolved in dimethyl sulfoxide, and anhydrous potassium carbonate was added to the resultant solution, followed by stirring at room temperature for one hour. Thereafter, ethyl 7-bromoheptanoate (169 mg) was added to the resultant mixture, and the mixture was stirred. The potassium carbonate was separated through filtration, and the resultant filtrate was poured into ice water. Hydrochloric acid was added to the resultant mixture so as to adjust the pH to 3, and then the mixture was subjected to extraction with chloroform twice. The resultant chloroform layer was washed with brine, and then dried over anhydrous sodium sulfate. The sodium sulfate was separated through filtration, and the resultant filtrate was concentrated to dryness under reduced pressure, followed by recrystallization, to thereby produce the target product (223 mg, yield: 72%).
