A novel bimolecular disproportionation in purine-N-oxides. A spontaneous autocatalytic and an anhydride induced disproportionation of 8-alkyl-7-hydroxyxanthines

8-Alkyl-7-hydroxyxanthines undergo in aqueous solution, near pH 5, an unusual spontaneous autocatalytic disproportionation. They yield the corresponding 8-alkylxanthines as the reduction product and 6-amino-5-nitrosouracil as the oxidation product. The disproportionation can also be induced by anhydrides at pH 4-12. The alkyl group at position 8 is essential for these reactions. Possible mechanisms are discussed.