Photochemical activities of N-nitroso carboxamides and sulfoximides and their application to DNA cleavage.

N-Nitroso compounds containing benzene, fluorene or fluorenone rings were synthesized. Photolysis of these compounds with 312-nm UV light provided the NO(*) species, the presence of which was corroborated by use of an EPR method and of 2-phenyl-4,4,5,5-tetramethylimidazolin-1-oxyl 3-oxide (PTIO) as a trapping agent. During irradiation of N-methyl-N-nitroso-9-fluorenone carboxamide (14 c) in the absence of PTIO, it underwent decomposition followed by recombination to give the heterocyclic nitric oxide radical 15. Incorporation of intercalating moieties endowed the N-nitroso compounds with DNA-cleaving ability through single-strand scission upon UV irradiation in a phosphate buffer (pH 5.0-8.0) under aerobic conditions.