Antioxidant action of a lipophilic nitroxyl radical, cyclohexane-1-spiro-2′-(4′-oxyimidazolidine-1′-oxyl)-5′-spiro-1″-cyclohexane, against lipid peroxidation under hypoxic conditions
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Nitroxyl radicals are known to act as radical scavenging antioxidants. In the present study, a lipophilic nitroxyl radical, cyclohexane-1-spiro-2′-(4′-oxyimidazolidine-1′-oxyl)-5′-spiro-1″-cyclohexane (nitroxyl radical I) was synthesized and its antioxidant capacity was assessed in comparison with a hydrophilic nitroxyl radical, 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (Tempol). Both nitroxyl radical I and Tempol inhibited methyl linoleate oxidation induced by free radicals, and the efficacy increased with decreasing partial pressure of oxygen, the effect being more pronounced for nitroxyl radical I than Tempol. Their hydroxylamines inhibited lipid peroxidation more effectively than their corresponding parent nitroxyl radicals. In liposomal membranes, a synergistic effect was observed in the combination of nitroxyl radical I with ascorbic acid, whereas only an additive effect was observed between Tempol and ascorbic acid. The present study suggests that nitroxyl radical I and its hydroxylamine may act as potent antioxidants, especially in combination with ascorbic acid under hypoxic conditions.
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methyl linoleate; nitroxyl radical I, cyclohexane-1-spiro-2′-(4′-oxyimidazolidine-1′-oxyl)-5′-spiro-1″-cyclohexane
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