The compound (17.6 mg) obtained in Example 25-1, the compound (13.2 mg) obtained in Example 19-2, and sodium cyanoborohydride (8.7 mg) were dissolved in anhydrous methanol (1.0 ml). The solution was then adjusted to pH 5 with the addition of acetic acid, followed by stirring at room temperature for 4 hours. The reaction solution was added with distilled water and then subjected to extraction with chloroform. After that, the organic layer was washed with saturated saline solution and dried with anhydrous sodium sulfate. The solvent was distilled off and the residue was then purified through silica gel preparative thin-layer chromatography (chloroform/methanol), thereby obtaining the subject compound (72.9 mg) as a yellow solid.
