Radiation-induced Oxidative Denitration of 2-Nitroimidazoles in Aqueous Solution

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The nitroimidazole derivatives such as misonidazole and metronidazole have been shown to enhance the radiosensitivity of hypoxic cells. These compounds are also known to exert a toxic effect selectively on hypoxic cells. The hypo-xic-cell toxicity may arise from the formation of reactive reduction products of the nitro compounds. Recently, we have reported the characteristics of the radiation-induced reduction of nitroimidazoles, demonstrating that unsubstituted 2-nitroimidazole is reduced by hydrated electrons (e^-_<aq>) to 2-aminoimidazole via a consecutive 6-electron process, whereas misonidazole bearing N1-alkyl sub-stituent to the hydroxyamino or oxime derivative via a 4-electron process. In the radiolysis of nitroimidazoles in aqueous solution, these compounds react with hydroxyl radicals (^・OH) as well as hydrated electrons (e^-_<aq>). In this paper we describe the finding that the nitro group of 2-nitroimidazole or miso-nidazole is eliminated by the reaction with OH radicals derived from radiolysis of water, the efficiency of which is almost the same as the reduction process by eaq.
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