Reactivity of imidazole moiety of fused aromatic ring for ionic and radical reaction species : Molecular stady for DNA damage

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Electrophilic amination of four 9-ethylguanine derivatives (1a-d) and seven 1-methylbenzimidazole derivatives (4a-g) with 2,4-dinitrophenoxyamine (DNPA) was carried out in DMF.N-amination proceeded at the imidazole moiety of these compounds with pKa's of more than 3.2 (1a, 1b, 4a, 4b, 4c, 4d). Treatment of these N-aminated derivatives (2a-b, 5a-d) with 0.1 N NaOH gave different results depending on their structures. In the guanine series, 9-ethyl-8-oxoguanine derivatives (3a, 3b)were obtained from N-aminated compounds (2a, 2b). In the benzimidazole series, no reaction proceeded with N-aminated compounds of 5a and 5b, whereas the benzo [1,2,4] triazine derivatives (6c, 6d) were obtained from N-aminated compounds (5c, 5d) , respectivery. It is not clear why the reactivity was different between purines (2a, 2b) and benzimidazoles (5c, 5d) although these have similar pKa values.