To 3 ml of a solution of 140 mg of 2-aminopyridine in ethanol was added 130 mg of sodium hydrogencarbonate and the resulting mixture was stirred at room temperature. Next, 2 ml of a solution of 360 mg of bromomethyl(10-methoxymethyl-10H-pyrazino[2,3-b][1,4]benzothiazin-8-yl)ketone in tetrahydrofuran was dropped thereinto and the resulting mixture was heated under reflux for 2 hours. Then the reaction mixture was brought back to room temperature and silica gel was added thereto. After distilling off the solvent under reduced pressure, the residue was purified by silica gel column chromatography (eluted with dichloromethane/methanol) to thereby give 200 mg of the title compound as yellow crystals.
