Spiroiminodihydantoin is a major product in the photooxidation of 2′-deoxyguanosine by the triplet states and oxyl radicals generated from hydroxyacetophenone photolysis and dioxetane thermolysis

Photolysis of hydroxyacetophenone and thermolysis of the corresponding dioxetane afford spiroiminodihydantoin rather than 4,8-dihydro-4hydroxy-8-oxo-2'-deoxyguanosine (4-HO-8-oxodG) through the oxidation of 2'-deoxyguanosine (dG) by triplet-excited hydroxyacetophenone and the peroxyl radicals derived thereof by a cleavage and subsequent oxygen trapping. The structure of the spiroiminodihydantoin is assigned by the SELINQUATE NMR technique, which unequivocally establishes the spirocyclic connectivity.