2-Chloro-3,4-dimethoxycinnamic acid (3.93 g, 16.2 mmol) was dissolved in 57 ml of pyridine. To the solution was added 1.26 ml (17.6 mmol) of thionyl chloride under ice cooling, and the mixture was stirred at 60° C. for 1.5 hours. Methylene chloride (58 ml) containing 2.50 g (14.7 mmol) of 5,6-diamino-1,3-dimethyluracil was added dropwise to the solution under ice cooling, and the reaction solution was stirred at room temperature for further 40 minutes. The deposited crystals were collected by filtration and the obtained crude crystals were dissolved in a mixture of 68 ml of an aqueous 2N sodium hydroxide solution, 68 ml of dioxane, and 34 ml of water, followed by heating under reflux for 30 minutes. After cooling, the solution was neutralized with a concentrated aqueous solution of hydrochloric acid, and the deposited crystals were collected by filtration. The collected crystals were washed with water, dried, and recrystallized from dimethylformamide/water to give 1.55 g (yield 30%) of Compound 107 as pale yellow needles.
