To 15 ml of a DMF solution containing 522 mg of [2-(2-fluoro-3-hydroxy-5-methoxyphenyl)-2-[4-(5-methyl-[1,2,4]oxadiazol-3-yl)phenylimino]-1-methylsulfanylethylidene]carbamic acid methyl ester (Example (3d)), 173 mg of potassium carbonate and 0.269 ml of (2-bromoethoxy)-t-butyldimethylsilane were added. The resulting mixture was stirred at room temperature for 15 hours, and then 25 ml of water and 25 ml of saturated ammonium chloride aqueous solution were added thereto. The mixture was extracted with 150 ml of ethyl acetate. The organic layer was washed with 50 ml of water and then with 50 ml of saturated brine and dried over anhydrous magnesium sulfate. The desiccating agent was removed by filtration, and the filtrate was concentrated under reduced pressure. The residue was purified by silica gel column chromatography (ethyl acetate-heptane) to give the title compound (210 mg).
