Synthesis of the derivatives of 6-amino-uracil labelled with C.

The radioactively labelled 6-amino-5-nitroso-uracil (1) and 5-acetyl-6-amino-1,3-dimethyl-uracil (2) were required for metabolic studies to assess their suitability as drug candidates. A common precursor for both compounds was [cyano- C]cyanoacetic acid (6), readily prepared from potassium [ C]cyanide. ACS reagents, namely, diethyl ether, acetic acid and acetic anhydride, had to be rigorously repurified to achieve a successful synthesis of C-labelled compounds on a tenth-of-a-milligramme scale.