Inami Keiko, Shiino Junko, Hagiwara Shin, Takeda Kei, Mochizuki Masataka
Faculty of Pharmaceutical Sciences, Tokyo University of Science, Yamazaki 2641, Noda-shi, Chiba 278-8510, Japan; Kyoritsu University of Pharmacy, Shibakoen 1-5-30, Minato-ku, Tokyo 105-8512, Japan.
Kyoritsu University of Pharmacy, Shibakoen 1-5-30, Minato-ku, Tokyo 105-8512, Japan.
Bioorg Med Chem. 2015 Jul 1;23(13):3297-302. doi: 10.1016/j.bmc.2015.04.058. Epub 2015 Apr 25.
N-Nitroso-N-methylurea (NMU) is a potent carcinogen and suspected as a cause of human cancer. In this study, mutagenic NMU was detected by HPLC after the transnitrosation of non-mutagenic N-nitrosoproline (NP) to N-methylurea in the presence of thiourea (TU) under acidic conditions. The structure of NMU was confirmed by comparing (1)H NMR and IR spectra with that of authentic NMU after fractionation by column chromatography. Furthermore, a fraction containing NMU formed by transnitrosation was mutagenic in Salmonella typhimurium TA1535. NMU was formed in the reaction of NP and N-methylurea in the presence of 1,1,3,3-tetramethylthiourea (TTU) or 1,3-dimethylthiourea in place of TU as an accelerator. The reaction rate constants (k) for NMU formation were correlated with their nucleophilicity of sulfur atom in thioureas. The N-methylurea concentration did not affect the NMU formation, whereas the rate of NMU formation correlated linearly with concentrations of NP, TTU and oxonium ion. The observed kinetics suggests a mechanism by which the nitroso group was transferred directly from the protonated NP to the thiourea then to N-methylurea to form NMU. The rate-determining step was the formation of the complex with the protonated NP and thiourea.
