2.27 g of the amorphous compound obtained in Example 108 was dissolved in 30 ml of dimethylformamide, to the solution were sequentially added 160 mg of 60% sodium hydride and 0.3 ml of methyl iodide with ice cooling, and the mixture was stirred for 90 minutes with ice cooling. After adding 80 ml of water, the reaction mixture was extracted with 100 ml of ethyl acetate, and the extract was washed with 80 ml of saturated sodium chloride aqueous solution, dried over magnesium sulfate and concentrated under a reduced pressure. The resulting residue was applied to a silica gel column and eluted with chloroform/methanol (60:1), to obtain 1.8 g of the title compound in a yellow amorphous form.
