The compound (67.5 mg) obtained in Example 124-4 was dissolved in anhydrous methanol (2.0 ml) and added with trimethyl orthoformate (0.0354 ml) and 2-imidazole carboxaldehyde (20.8 mg), followed by stirring at room temperature for 2 hours under a nitrogen atmosphere. Subsequently, the solution was added with sodium borohydride (12.3 mg) in an ice bath and then stirred at room temperature for 1 hour. After completion of the reaction, a saturated aqueous ammonium chloride solution was added to the solution, and the whole was stirred. The solution was subjected to extraction with chloroform and the extract was then washed with a saturated aqueous sodium bicarbonate solution and saturated saline solution. The organic layer was dried with anhydrous sodium sulfate. The solvent was distilled off and the residue was then purified through silica gel column chromatography (chloroform/ethyl acetate), thereby obtaining the subject compound (39.0 mg) as a yellow oily substance.
