The mutagenicity of N-nitrosamines is usually detected in the presence of an S9 mix, which includes cytochrome P450. The mutagenicity of N-nitrosodialkylamines is induced by Fe 2+-Cu 2+-H 2O 2, which can be used as a chemical model for cytochrome P450. However, a direct-acting mutagen derived from N-nitroso-N-methylbutylamine (NMB) by the same oxidation system has not been reported. In this study, we determined the structure of a direct-acting mutagen obtained from the reaction of NMB with Fe 2+-Cu 2+-H 2O 2 by comparing its instrumental data ( 1H, 13C NMR and IR) with that from the synthesized compound. We confirmed that the direct-acting mutagen derived from NMB with Fe 2+-Cu 2+-H 2O 2 was 5-methyl-5-nitro-1-pyrazoline 1-oxide. Furthermore, we investigated the mechanism of the mutagenicity by 5-methyl-5-nitro-1-pyrazoline 1-oxide using Salmonella typhimurium strains. The mutagenicity of 5-methyl-5-nitro-1- pyrazoline 1-oxide in S. typhimurium YG7108, which is deficient O 6-alkylguanine alkyltransferase, was higher than that in the parent strain S. typhimurium TA1535, indicating that the mutations are caused by DNA alkylation.
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