Liver microsomal metabolism of N-methylcarbazole: Structural identification of the four major metabolites of N-methylcarbazole using ¹H Fourier transform NMR spectroscopy

¹H Fourier transform NMR spectroscopy, in conjunction with mass spectrometry, was employed for the identification of the four major metabolites formed from N-methylcarbazole, a cocarcinogen present in tobacco smoke, after incubation in vitro with rabbit liver microsomes. The four metabolites were separated by high pressure liquid chromatography and characterized by ultraviolet spectroscopy, mass spectrometry, and ¹H Fourier transform NMR spectroscopy. Mass spectrometry established that each of the metabolites contained an oxygen atom and ¹H Fourier transform NMR spectroscopy was used to identify the positional isomers of the hydroxylated N-methylcarbazole. It was used to identify the positional isomers of the hydroxylated N-methylcarbazole. It was established from comparison of the ¹H Fourier transform NMR spectra of the isolated metabolites of N-methylcarbazole with those of the corresponding spectra for known synthetic compounds that the four major metabolites formed in vitro were: 1-hydroxy-N-methylcarbazole, 2-hydroxy-N-methylcarbazole, 3-hydroxy-N-methylcarbazole, and N-hydroxymethylcarbazole.