To 10 mL of a chloroform solution containing 500 mg of 1-(2-(4-aminopiperidin-1-yl)ethyl)-7-methoxyquinoxalin-2(1H)-one and 200 mg of 4-ethylbenzaldehyde, 100 mg of acetic acid were added, and stirred at room temperature for 1 hour. To the reaction mixture, 526 mg of sodium triacetoxyborohydride was added, and stirred for 15 hours. Aqueous saturated sodium hydrogen carbonate solution was added, the organic layer was separated. The organic layer was washed with aqueous saturated sodium chloride solution, dried over anhydrous magnesium sulfate, and the solvent was removed under reduced pressure. The residue thus obtained was purified by silica gel column chromatography [Silica Gel; Kanto Chemical Co., Inc., Silica Gel 60N, eluent; chloroform:methanol=10:1], to give 0.32 g of 1-(2-(4-(4-ethylbenzylamino)piperidin-1-yl)ethyl)-7-methoxyquinoxalin-2(1H)-one as a brown oil.
