Nitrosation of 1-(4-chlorophenyl)-3-propyl-6-aminouracil (I) by means of sodium nitrite and formic acid in hot formamide afforded the 5-nitroso derivative (II). This was reduced with sodium dithionite at 100 C to produce the intermediate diamino uracil (III) which, on further heating at 190 C in formamide, gave rise to the title xanthine.