6-[1-(3-Amino-2-pyridyl)piperazine-4-yl-carbonyl]nicotinic acid (0.5 g) was added to a co-solvent of tetrahydrofuran (10 ml) and methylene chloride (10 ml) and with the successive addition of 1,3-dicyclohexylcarbodimide (0.65 g) and 1-hydroxybenzotriazole (0.23 g) at 15˜20° C., the mixture was stirred for 2 hours. With the addition of ethanolamine (0.18 ml), the mixture was stirred again at 20˜25° C. for 2 hours. Methylene chloride (30 ml) was added again to the mixture, washed with water 3 times, dried over magnesium sulfate and concentrated under reduced pressure. The concentrated residue was treated with ether for crystallization. The solid was recrystallized with ethanol and hexane to give a desired compound of 0.44 g (yield: 78%).
