Hydroxylamine and methoxyamine mutagenesis: tautomeric equilibrium of the promutagenic, N6-methoxyadenosine in solvents of different polarities.

Ultraviolet (UV) and Infrared (IR) spectroscopy have been applied to a study of the tautomeric equilibrium, in solvents of varying polarities and differing hydrogen bond donor-acceptor properties, of the promutagenic analogue N6- methoxyadenosine , the product of the reaction of the mutagen methoxyamine with adenosine. In the non-polar solvent CCl4, the analogue is predominantly in the amino form, with KT approximately 10. On transfer from CCl4 to chloroform, dimethyl sulfoxide, and water, the equilibrium is shifted stepwise towards the imino form, attaining a KT approximately 10 in favour of the imino species in aqueous medium. Both the UV and, particularly, the IR spectra exhibit two sets of absorption bands which were assigned to the respective tautomers , in dynamic equilibrium with each other. The significance of the foregoing results in the mechanism of hydroxylamine (and methoxyamine) mutagenesis is considered. It is also shown that base pairing of each tautomeric species is significantly dependent on the conformation of the exocyclic N6-methoxy group. It is further demonstrated that infrared spectroscopy provides data which both supplement and extend those obtained by NMR spectroscopy, under conditions where application of the latter is technically limited.