Structure and mutagenicity of a direct-acting mutagen derived from the reaction of N-nitroso-N-methylbutylamine with hydroxyl radical

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.