4-[1-(3-Amino-2-pyridyl)piperazin-4-yl-carbonyl]benzoic acid methyl ester (4 g) was dissolved in methanol (80 ml) and then, acetaldehyde (1.7 ml) and acetic acid (4 ml) were added at 0° C. The solution was stirred at 0° C. for 30 minutes. Then, with the addition of sodium cyanoborohydride (2.2 g), the solution was stirred at 0~5° C. for 2 hours. Excess of water was added gradually, and the solution was neutralized (pH=~8) by addition of aqueous 3N-sodium hydroxide. The mixture was stirred for 1 hour and filtered, and the crude solid was recrystallized using methanol and ether to give 3.51 g (yield: 81%) of the desired compound.
