Molecular Pharmacology, Vol 17, 128-136, Copyright © 1980 by the American Society for Pharmacology and Experimental Therapeutics

Liver Microsomal Metabolism of N-Methylcarbazole: Structural Identification of the Four Major Metabolites of N-Methylcarbazole using ¹H Fourier Transform NMR Spectroscopy

¹ Departments of Pharmacology and Biochemistry, Northwestern University Medical and Dental Schools, Chicago, Illinois 60611

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 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.

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ACKNOWLEDGMENTS The authors would like to thank Dr. Chiadao Chen for his many helpful discussions and his contributions to the synthesis of some of the compounds. We also thank Dr. Jaroslav Majer for his helpful suggestions and encouragement. We are indebted to Dr. John Strong and Dr. Sam Lucas for their expert assistance with the mass spectrometry.