To a suspension of N-{ 1-butyl-4-(3-hydroxyphenyl)-1,2-dihydro-2-oxo-1,8-naphthyridin-3-yl}-N'-(2,6-diisopropylphenyl)urea (200 mg, 0.4 mmol), potassium carbonate (166 mg, 1.2 mmol), and sodium iodide (5 mg) in DMF (10 ml) was added 3-dimethylaminopropyl chloride hydrochloride (63 mg) at room temperature, and the mixture was stirred at 60°-70° C. for 10 hours. After allowed to stand for cooling, the mixture was poured into water, extracted with ethyl acetate, washed with water, washed with a saturated aqueous sodium chloride solution, and dried over anhydrous magnesium sulfate. The residue was concentrated under reduced pressure, and purified by silica gel column chromatography (10% methanol in chloroform) to give the title compound (88 mg, 0.15 mmol).
