Anomalous reaction of oxide radical ion with 5-azacytosines: An experimental and theoretical study

The reactions of oxide radical ion ( O - ) with 5-azacytosine (5AC) and 5-azacytidine (5ACyd) in aqueous medium were studied using the pulse radiolysis technique and quantum chemical calculation using density functional theory (DFT). It is demonstrated that the major reaction pathway is the addition of O - to the ring nitrogen of 5AC, followed by a fast protonation of adducts by water. Only a minor percentage (<18%) undergoes an electron transfer reaction. The similarity in the reaction mechanism of O - (addition to azacytosine) and OH (which generally participates in an addition reaction) is an interesting observation and is quite unusual in the case of heterocyclic compounds.