5-cyanoimino-4-oxomethylene-4, 5-dihydroimidazole and 5-cyanoamino-4-imidazolecarboxylic acid intermediates in nitrosative guanosine deamination: Evidence from O(super 18)-labeling experiments

The nitrosative deaminations (37 0C, NaNO2, NaAc buffer, pH 3.7) of guanosine 1r in (O(super 18))-water (97.65) and (6-O(super 18))-1r in normal water are studied. The results show that oxanosine is formed via 5-cyanoimino-4-oxomethylene-4, 5-dihydromidazole, 5, and its 1,4-addition product 5-cyanoamino-4-imidazolecarboxyllic acid, 6.