0.6 g of 1-ethoxycarbonyl-2-{4-(3-methoxypropoxy)-3-methylpyridine-2-yl}methylthiobenzimidazole was dissolved in 20 ml of dichloromethane to obtain a solution. 0.4 g of m-chloroperbenzoic acid was added to the solution at -45° C. After one hour, 0.3 g of triethylamine and 20 ml of a saturated aqueous solution of sodium hydrogencarbonate were added to the resulting mixture. The obtained mixture was stirred at a room temperature for 30 minutes. The dichloromethane layer was separated, washed with a saturated aqueous solution of sodium hydrogencarbonate twice, dried over magnesium sulfate and filtered. The filtrate was concentrated to obtain a residue. This residue was purified by silica gel column chromatography to obtain 0.21 g of the title compound as a yellow oil.
