Nitrosative adenine deamination: Facile pyrimidine ring-opening in the dediazoniation of adeninediazonium ion

[GRAPHIC] Dediazoniation of adeninediazonium ion, 1, forms the heteroaromatic cation, 2. Ab initio studies at the CCSD(fc)/6-31G**//MP2(full)/6-31G** level now reveal that the cyclic cation 2 is kinetically and thermodynamically unstable with respect to the pyrimidine ring-opened cation, 3. The results suggest that 4-cyano-5-isocyano-imidazole, 4, and 4,5-dicyanoimidazole, 5, might be formed to some extent in nitrosative deaminations of adenine.