Trans-3-(4-aminocyclohexylcarbonylamino)-N-(5-chloropyridin-2-yl)benzofuran-2-carboxamide dihydrochloride (125 mg) obtained in Example 219 is suspended in dichloromethane (10 ml), and thereto is added triethylamine (102 μl) under ice-cooling, and the mixture is stirred for several minutes. Then, about 25% aqueous glutaraldehyde solution (150 mg) and sodium triacetoxy borohydride (155 mg) are added successively, and the mixture is stirred under ice-cooling for 2 hours. To the reaction solution is poured a saturated aqueous sodium hydrogen carbonate solution, and the mixture is extracted with chloroform. The organic layer is washed successively with water and a saturated brine, dried over sodium sulfate, and the solvent is evaporated under reduced pressure. The resulting residue is purified by NH-silica gel column chromatography (eluent: n-hexane/ethyl acetate=3/1, then 1/1) to give trans-3-[4-(piperidin-1-yl)cyclohexylcarbonylamino]-N-(5-chloropyridin-2-yl)benzofuran-2-carboxamide (106 mg). Subsequently, this product is dissolved in chloroform/methanol (5/1, 6 ml), and 4N hydrogen chloride in ethyl acetate (5 ml) is added thereto under ice-cooling. The reaction solution is concentrated under reduced pressure, and the resulting residue is suspended in diethyl ether, and collected by filtration to give the title compound (107 mg).
