A solution of 2-(5-amino-2-propoxyphenyl)-8-azapurin-6-one (1.5 g) in anhydrous N-methylpyrrolid-2-one (7 ml) was treated with isopropyl isocyanate (0.5 g). The mixture was kept at room temperature overnight and then added to dilute aqueous ammonia solution (50 ml; 2 N). The resulting solution was acidified by treatment with concentrated hydrochloric acid, and the solid which separated was crystallised from methanol to give 2-[2-propoxy-5-(3-isopropylureido)phenyl]-8-azapurin-6-one (1.0 g), in the form of colourless prisms, m.p. 203°-205° C. (with decomposition).
