The compound (1.18 g) obtained in Example 121-6 was dissolved in anhydrous dichloromethane (25 ml) and added with Dess-Martin periodinane (1.82 g), followed by stirring at room temperature for 2 hours. After completion of the reaction, a sodium thiosulfate aqueous solution and a saturated aqueous sodium bicarbonate solution were added to the solution, and the whole was stirred. Then, the solution was extracted with chloroform and the extract was then washed with an aqueous mixture solution of a sodium thiosulfate aqueous solution and a saturated sodium bicarbonate aqueous solution. Then, the organic layer was dried with anhydrous sodium sulfate and the solvent was distilled off. The residue was purified through silica gel column chromatography (hexane/ethyl acetate), thereby obtaining the subject compound (981 mg) as a white solid.
