Spiroiminodihydantoin nucleoside formation from 2'-deoxyguanosine oxidation by [(18)O-labeled] singlet molecular oxygen in aqueous solution.

The main singlet molecular oxygen ((1)O(2)) oxidation products of free 2'-deoxyguanosine (dGuo) in aqueous solution were identified as a pair of diastereomeric spiroiminodihydantoin 2'-deoxyribonucleosides (dSp) together with 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo). In the present work, evidence is provided from (18)[(1)O(2)] and H(2) (18)O labeling experiments, using HPLC-ESI-MS/MS, that the formation of dSp is explained by the addition of water to a reactive quinonoid intermediate, and a second reaction pathway leading to dSp involves (1)O(2) oxidation of initially generated 8-oxodGuo.