Acetylation of phenolic derivatives of 7H-dibenzo[c,g]carbazole: identification and quantitation of major metabolites by rat liver microsomes.

Acetylation stabilized the phenolic metabolites of 7H-dibenzo[c,g]carbazole (DBC) and made it possible to accumulate greater amounts of metabolites for comprehensive chemical structural elucidation and quantification without the use of radiolabeled DBC. High-resolution mass spectral data and 1H NMR and fluorescence spectra were used to confirm the existence of 5-OH-DBC, 3-OH-DBC, 1-OH-DBC, and the oxidative dimer, 6,6'-bis-(5-OH-DBC), in the acetylated metabolite mixture formed in vitro by 3-methylcholanthrene-induced rat liver microsomes. Using the synthesized acetoxy-DBC derivatives as standards, the HPLC external standard method was employed for quantitation of the major DBC metabolites after acetylation. The quantities of 5-OH-DBC, 3-OH-DBC, 1-OH-DBC, and DBC in the metabolite mixture determined using the external standard method were found to agree with those calculated using the radiometric method. Acetylation is a promising nonradiometric qualitative and quantitative technique for further metabolism studies of DBC and analogues which produce unstable monohydroxylated metabolites.