The compound (225.3 mg) obtained in Example 103-3 was dissolved in methanol (6.76 ml). Then, the solution was added with the compound (165.0 mg) obtained in Example 1-2 and trimethyl orthoformate (304.8 mg), followed by stirring at room temperature for 18 hours. Sodium borohydride (108.7 mg) was added to the solution under ice-cooling, followed by stirring at room temperature for 0.5 hours. The reaction solution was added with water and subjected to separation/extraction with chloroform. Then, the extract was washed with saturated saline solution and dried with anhydrous sodium sulfate, followed by concentration under reduced pressure. The residue was purified through silica gel column chromatography (chloroform/methanol), thereby obtaining the subject compound (297.6 mg) as a colorless oily substance.
