DNA cleavage induced by alkoxyl radicals generated in the photolysis of N-alkoxypyridinethiones.

The photolysis of N-isopropoxypyridine-2-thione (1b) and of N-tert-butoxypyridine-2-thione (1c) generated alkoxyl radicals as confirmed by trapping experiments with DMPO and subsequent EPR spectroscopy. Upon UVA irradiation, the alkoxyl-radical sources induce strand breaks in supercoiled pBR 322 DNA, which was analyzed by gel electrophoresis. The participation of type I (electron transfer, H abstraction) or type II (1O2) photosensitization in the DNA cleavage by the oxyl-radical sources 1a-d or their photoproducts could be excluded. The present study establishes unequivocally that alkoxyl and benzoyloxyl, as well as hydroxyl radicals, cause strand breaks in DNA and, thus, may play a significant role in the DNA cleavage by peroxides.