Compound 1 (40 mg, 0.10 mmol) obtained in Example 1 was dissolved in ethanol (5 mL), and O-methylhydroxyamine hydrochloride (25 mg, 0.30 mmol) and pyridine (0.024 mL, 0.03 mmol) were added thereto, followed by stirring at room temperature for 3 hours. A saturated aqueous ammonium chloride solution was added to the reaction mixture, followed by extraction with ethyl acetate twice. The organic layer was dried over anhydrous sodium sulfate, and concentrated under reduced pressure to yield a residue. The residue was purified by preparative thin layer chromatography to obtain the title compound (39 mg, 93%) as an E/Z mixture.
