To a solution of 491 mg (1.5 mmol) of 3-[4-(4-pyridylthio)butyl]quinazoline-2,4(1H,3H)-dione and 287 mg (1.8 mmol) of 4-chloromethylthiopyridine in 15 ml of dimethylformamide, 0.27 ml (1.8 mmol) of 1,8-diazabicyclo[5.4.0]-7-undecene was added, and the mixture was stirred at 80° C. for 16 hours. After cooling, water was added to the reaction mixture, and the mixture was extracted with ethyl acetate. The extract was dried and the solvent was distilled off. The residue was purified by flash column chromatography (eluent: ethyl acetate/hexane =2:1 to 4:1 to ethyl acetate) to give 0.315 g of the desired product (46.7% yield, colorless oil).
