Abstract
A manganese porphyrin, manganese(III)‐bis(aqua)‐meso‐tetrakis(4‐N‐methylpyridiniumyl)porphyrin, in the presence of KHSO~5~ is able to perform deoxyribose or guanine oxidation depending on its mode of interaction with DNA. These two reactions involve an oxygen‐atom transfer or an electron transfer, respectively. The oxidative reactivity of the manganese‐oxo porphyrin was compared on short oligonucleotide duplexes of different sequences. The major mechanism of DNA damage is due to deoxyribose hydroxylation at a site of strong interaction, an (A**⋅T)~3~ sequence. Guanine oxidation by electron transfer was found not to be competitive with this major mechanism. It was found that a single intrastrand guanine was three orders of magnitude less reactive than an (A⋅T)~3~ sequence. The reactivity of a 5′‐GG sequence was found to be intermediate and was estimated to be two orders of magnitude less than that of an (A⋅**T)~3~ site. Short oligonucleotide duplexes, as double‐stranded‐DNA models, proved to be convenient tools for the study of the comparative reactivity of this reagent toward different sequences of DNA. However, they showed a particular reactivity at their terminal base pairs (the “end effect”) that biased their modeling capacity for double‐helix‐DNA models.