To a solution of N-{1-butyl-4-(3-hydroxyphenyl)-1,2-dihydro-2-oxo-1,8-naphthyridin-3-yl}-N'-(2,6-diisopropylphenyl)urea (1000 mg, 1.95 mmol) and 1-bromo-3-chloropropane (460 mg, 2.93 mmol) in DMF (10 ml) was added potassium carbonate (673 mg, 4.88 mmol), and the mixture was stirred at 50°-60° C. for 6 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 sodium sulfate. The residue was concentrated under reduced pressure, purified by silica gel column chromatography (ethyl acetate:hexane=50:50), and crystallized from hexane to give the title compound (1020 mg, 1.73 mmol) as a colorless powder.
