Electrochemical studies and DNA damaging effects of the benzotriazine-N-oxides

The electrochemical behaviour of eight benzotriazine 1,4 di-N-oxides has been examined and compared with the mono- and zero-N-oxides. The di-N-oxides all show two reduction steps, an irreversible followed by a quasi-reversible response assigned to the 4 electron reduction of both N-oxide groups, followed by the 2 electron reduction of the benzotriazine ring. Mono- and zero-N-oxides show only a single, quasi-reversible reduction step, similar in character to the second reduction of the di-N-oxides. This has been assigned to reduction of the benzotriazine ring, with the available, redox-active, N-oxide group of the mono-N-oxide complex being reduced at less negative potentials, but only after ring reduction, hence only a single electrode response. The importance of reductive activation of the N-oxide group has been examined using a phi X174 double transfection technique which assays biologically relevant DNA damage. For the di-N-oxides, no effect on DNA was recorded under oxic conditions, however, DNA damage was marked under anoxic reduction conditions. The extent of DNA damage was found to increase with the acidity of the medium, suggesting the protonated form of the reduction product as being responsible for the cytotoxic action. The mono-N-oxide was shown to be biologically inactive under all conditions.