Mass spectrometric analysis of 7‐sulfoxymethyl‐12‐methylbenz[a]anthracene and related electrophilic polycyclic aromatic hydrocarbon metabolites

Abstract

The Meso-region theory of polycyclic aromatic hydrocarbon (PAH) carcinogenesis predicts that the development of pronounced carcinogenicity depends on the introduction of a good leaving group on alkyl side-chains attached to the exceptionally reactive meso-anthracenic or L-region positions of PAHs. Thus, the first step in carcinogenesis by methylated PAHs such as 7,12-dimethylbenz[a]anthracene (DMBA) would be the hydroxylation of the L-region methyl groups, particularly the 7-methyl group. The second would be the formation of a metabolite, e.g. a sulfate ester, which is expected to be a good leaving group capable of generating a highly reactive benzylic carbocation. 7-Hydroxymethyl-12-methylbenz[a]anthracene (7-HMBA) is a metabolite of DMBA, and sulfation of 7-HMBA to a 7-sulfoxymethyl metabolite (7-SMBA) is a known Phase II metabolic process designed to facilitate excretion, but actually enabling more destructive side-reactions. These side-reactions occur with generation of an electrophilic 7-methylene carbonium ion, and/or by in vivo halide exchange to provide neutral side-products more capable of entering cells, especially those of DMBA target tissues. Electrospray ionization mass spectrometry (MS) enabled us to visualize 7-SMBA as an intact m/z 351 conjugate anion by negative mode, and as a released m/z 255 carbonium ion by positive mode. Upon prolonged refrigeration, 7-SMBA accumulated an m/z 383 photooxide, which appeared capable of re-evolving the starting material as visualized by tandem quadrupole MS, or MS/MS. The 7-SMBA carbonium ion provided interpretable fragments when studied by fragment ion MS/MS, including those representing the loss of up to several protons. Subtle differences in this property were encountered upon perturbing 7-SMBA, either by warming it at 37 degrees C for 2 h or by substituting the initial sulfoxy group with an iodo group. Side-reactions accounting for such proton losses are proposed, and are of interest whether they occur in the mass spectrometer, in solution or both; these proposals include acidity at the 12-methyl position and cyclization between the 12-methyl group and the adjacent C-1 position. It is also suggested that such side-reactions may comprise one route to relieving steric strain arising between the 12-methyl group and the angular benzo ring of 7-SMBA.

Room temperature fluorescence spectroscopy of benzo[a]pyrene metabolites on octadecyl extraction membranes

“…Ultraviolet-visible absorption and RTF detection have been widely used with both HPLC and CE [40][41][42][43][44][45]. The ultimate specificity belongs to high-resolution MS either coupled to gas chromatography (GC-MS) or HPLC (HPLC-MS) [46][47][48][49][50][51].…”

Chemical Structure Determination of DNA Bases Modified by Active Metabolites of Lucidin-3-O-primeveroside

“…Sulfotransferases (SULTs) are one of the phase II detoxification enzymes which catalyze the transfer of a sulfonyl group from 3′-phosphoadenosine-5′-phosphosulfate (PAPS) to the hydroxyl, sulfhydryl, amino, or N -oxide groups of various substrates . As known in some compounds, the dissociation of the sulfate ion following sulfate conjugation of benzylic alcohol results in a reactive carbocation intermediate, and it has been thought that SULT-mediated reactions could generate electrophilic reactants in a similar manner , . Since Luc possesses benzylic alcohol in its structure, it has been postulated that after sulfate conjugation a reactive carbocation or quinone methide formed in Luc at the benzylic position could react with DNA bases.…”