A reaction was carried out in 30 mL of potassium carbonate suspension with (R)-2-chloro-7-ethyl-8-isopropyl-7,8-dihydropteridin-6(5H)-one (27.5 mmol, 7 g) and dimethyl carbonate (41 mmol, 5.7 g). The reaction mixture was placed in an autoclave, heated to 130 °C and maintained for 5 hours. Upon completion of the reaction, the mixture was cooled to 25°C. Subsequently, 25 mL of deionized water and 15 mL of ethyl acetate were added and mixed with stirring. The organic phase was concentrated by distillation under reduced pressure. To the residue, 25 mL of ethanol and 45 mL of deionized water were added and heated to 60°C to dissolve. The solution was cooled to room temperature and the precipitate was collected by filtration. The precipitate was washed with a mixture of softened water and ethanol (2:1 volume ratio). Finally, the product was dried in a vacuum drying oven at 50 °C to afford (R)-2-chloro-7-ethyl-8-isopropyl-5-methyl-7,8-dihydropteridin-6(5H)-one (6 g, 82% yield).
