Selective Oxidation of Methyl Substituted 1,3-Dimethyllumazine Derivatives with Nitric acid

Usually the alkyl side chains of the pteridine system are oxidized to the corresponding pteridine carboxylic acid with potassium permanganate.1 However the oxidation of 1,3-dimethyllumazine (1,3-dimethyl-2,4-dioxopteridine) deriva-tives with potassium permanganate yielded the correspond-ing carboxylic acids in low yield2 because 1,3-dimethyl-lumazines are insoluble in water and the pyrimidine moeity in the pteridine ring is cleaved under alkaline medium converting them to pyrazine derivatives.3 Recently we found that the oxidation of 6-acetyl-1,3,7-trimethyllumazine (1)4 strongly depended upon the concentration of the nitric acid employed. 1 was converted to 1,3,7-trimethyllumazine-6-carboxylic acid by heating under reflux with 10 % nitric acid. On the other hand, concentrated nitric acid of more than 50 % was able to completely oxidize both 6-acetyl and 7