Guanine oxidation: NMR characterization of a dehydro-guanidinohydantoin residue generated by a 2e-oxidation of d(GpT).

The Mn-TMPyP/KHSO(5) system was used to oxidize guanine contained within a dinucleoside monophosphate d(GpT). To identify the guanine oxidation product having a mass with 4 amu above the mass of guanine itself, this relatively unstable compound was reduced to a more stable one. The ESI/MS and NMR data allowed us to propose a dehydro-guanidinohydantoin structure for the (G+4) guanine oxidation product.