Altered aromatic metabolites

Altered Aromatic Metabolites. Loss of parent compound is insufficient evidence to support the occurrence of biodegradation. Frequently, the disappearance of the parent aromatic compound results in the formation of an altered aromatic metabolite. This product indicates that, although biotransformation has taken place, biodegradation has not. An example is the anaerobic O-demethylation of chlorinated guaiacols to chlorocatechols mediated by the acetogenic bacteria, Acetobacterium woodii and Eubacterium limosum (37). 

The structure of some phenolic metabolites of 3-nitrofluoranthene (231a) and its 2-nitro isomer have been analyzed by one-dimensional and two-dimensional NMR at 500 MHz. Chemical shifts suggest that the nitro group is not strictly coplanar with the aromatic ring system in solution and that metabolism at a distant site can alter the conformation about the C—N bond of the nitro group492. 

PAHs and aromatic amines are carcinogenic and are rapidly converted in the liver into a suite of metabolites. Considering that the point of metabolism is to alter the solubility of the compound such that it can be excreted, it stands to reason that detoxification would not only decrease the lipid solubility of the PAH but also decrease its reactivity, or in other words, its propensity to form DNA adducts. However sensible that may seem, the converse is actually true. Highly reactive metabolites, such as epoxides and quinones, are often formed during Phase I metabolism. These chemicals actually increase, rather than decrease, chemical reactivity. Consequendy, as many PAHs are metabolized and prepared for excretion, their carcinogenicity may actually increase. 

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