1.16 g (7.5 mmol) of 2-amino-4,6-dimethoxypyrimidine was dissolved in 20 ml of dry tetrahydrofuran, and 1.07 g (7.5 mmol) of chlorosulfonyl isocyanate was dropwise added thereto at -40° C. The reaction temperature was raised to 0° C., and then the reaction mixture was cooled again to -40° C. Then, a mixture comprising 1.16 g (7.5 mmol) of 1-methyl-3-n-propyl-2-iminoimidazolidin-4-one, 0.83 g (8.2 mmol) of triethylamine and 20 ml of dry tetrahydrofuran, was added thereto. The reaction temperature was raised to room temperature, and the mixture was further stirred at the same temperature for 2 hours. Then, the solvent was distilled off under reduced pressure, and then 100 ml of water was added to the obtained residue. The mixture was extracted three times with 100 ml of chloroform. Then, the chloroform layer was washed with water and then dried over anhydrous sodium sulfate. The solvent was distilled off under reduced pressure, and precipitated crystals were washed with a solvent mixture of ethyl ether/acetonitrile and collected by filtration to obtain 0.16 g of desired 1-(1-methyl-3-n-propylimidazolidin-4-one-2-sulfonylimino)-3-(4,6-dimethoxyprimidin-2-yl)urea. Melting point: 96°-98° C.
