Dipropylamine (363 mg) was dissolved in anhydrous methanol (20 ml) and then added with sodium cyanoborohydride (281 mg), trimethyl orthoformate (0.490 ml), and the compound (981 mg) obtained in Example 121-7, followed by stirring overnight at room temperature under a nitrogen atmosphere. After completion of the reaction, the solvent was distilled off. Then, the residue was dissolved in chloroform and added with a saturated aqueous sodium bicarbonate solution, followed by stirring. The solution was extracted with chloroform and the extract was then washed with a saturated aqueous sodium bicarbonate solution and saturated saline solution. After that, the organic layer was dried with anhydrous sodium sulfate. Subsequently, the solvent was distilled off and the residue was then purified through silica gel column chromatography (chloroform/ethyl acetate), thereby obtaining the subject compound (1.28 g) as a brown liquid.
