Compound 1 (1.00 g, 1.96 mmol) obtained in Example 1 was dissolved in 20 ml of dimethylformamide. To the solution was dropwise added 0.29 ml (3.92 mmol) of thionyl chloride under ice-cooling, and the resulting mixture was stirred at room temperature for 10 minutes. After ice-cooling, 1.02 ml (9.80 mmol) of diethylamine was added dropwise to the mixture, and the resulting mixture was stirred at room temperature for one hour. The mixture was poured into 50 ml of water and extracted three times with 20 ml of chloroform. The extract was washed successively with water and a saturated aqueous solution of sodium chloride, and dried over anhydrous sodium sulfate, followed by evaporation under reduced pressure. The residue was purified by column chromatography (eluent: 65% ethyl acetate/hexane), followed by recrystallization from cyclohexane/toluene to give 320 mg (yield 30%) of Compound 2 as a pale yellow powder.
