Photobiological model studies on perester and pyridone tert-butoxyl radical sources (photo-Fenton-type reagents): 2′-deoxyguanosine modification by methyl radicals generated through competitive β-cleavage in aqueous media

Abstract

In aqueous solution, UV irradiation of the photo-Fenton-type reagents perester 1 and N-tert-butoxypyridone 2 leads to the formation of tert-butoxyl radicals and methyl radicals as confirmed by product studies and by spin trapping with 5,5-dimethyl-1-pyrroline N-oxide (DMPO), followed by EPR spectroscopy. The methyl radicals result from the initially released tert-butoxyl radicals through β-cleavage, a fragmentation pathway, which dominates at lower DMPO concentrations. In the presence of 2′-deoxyguanosine (dG), both photochemical radical sources afford 8-MedG [(2.3 ± 0.3)%] and N⁷-MedG [(0.27 ± 0.05)%] as modified products, whereas the direct reaction of the tert-butoxyl radicals with dG cannot compete with this β-cleavage process.