Benzo pyrene, carcinogenicity structure

Being interested here in the volatile components of coffee aroma, we shall arbitrarily limit the list of the aromatic hydrocarbons to tricyclic structures. The higher fused polycyclic hydrocarbons (fluoranthene [206-44-0], pyrene [129-00-0], chrysene [218-01-9], benz[ ]anthracene (1,2-benzanthracene) [56-55-3], benz[< ]acephenanthrylene (3,4-benzofluoranthene) [205-99-2], benzo[ ]pyrene (3,4-benzopyrene, 3,4-BP) [50-32-8], benzo[e]pyrene (1,2-benzopyrene) [192-97-2], perylene [198-55-0], benzo[g,/i,/]perylene (1,12-benzopyrene) [191-24-2], and dibenz[ ,//]anthracene (1,2,5,6-dibenzanthracene) [53-70-3]) cannot be considered as a part of the aroma. However, as some of these, specially benzo[o pyrene, are known for carcinogenic properties, they have been particularly analyzed in food subject to roasting or smoke-curing. 

Fig. 1. Structures of benzo[<2]pyrene, 3-methylcholanthrene and dioxin. Benzo[<2]-pyrene and 3-methylcholanthrene are PAH compounds, but dioxin is not. Benzo [ ] pyrene is converted to the ultimate carcinogen BPDE by CyplAl.

Benzo[a]pyrene, a molecule with five, fused, hexagonal rings, is among the most carcinogenic of the polycyclic aromatic hydrocarbons (PAHs). Such biological activity may be related to the electronic structure of benzo[a]pyrene and its metabolites. Ionization energies of these molecules therefore have been investigated with photoelectron spectroscopy [28]. 

Recent structure-activity studies of 1-alkylbenzo[a]pyrenes also suggest that DNA intercalation of benzo[a]pyrene (BP) metabolites plays a role in the mechanism of BP carcinogenesis (38). The addition of bulky alkyl groups at the 1-position of BP, which inhibit DNA intercalation of 1-alkyl-BP metabolites (19), causes a reduction in carcinogenic activity. 

The low-molecular weight hydrocarbons (mol wt <216) are regarded as non-carcinogenic, unlike many heavy PAHs. Furthermore, the degree of carcinogenic activity depends on the structure of the compound. The maximum limits for PAH concentration in air and water samples, therefore, have been established for individual PAHs. Benzo[a]pyrene (BaP, Figure 13.16) is... 

In 1775, Pursevil Pott first noted that the compounds associated with soot caused scrotal cancer in British chimney sweeps (] ). Not having modern methods of Instrumental analysis available to him, Pott was unable to specify the chemical structures of these compounds. It remained until 1933 before Cook et al. identified the exact structure of benzo[a]pyrene and demonstrated its carcinogenicity ( ). Thus, polycyclic aromatic hydrocarbons (PAH) are one of the few groups of compounds which are known to be carcinogenic to man. 

Because the genotoxic activity of benzo[a]pyrene is well established, it is frequently used as a positive control to demonstrate the sensitivity of various test systems to detect the genotoxic action of unknown compounds. It also serves as the model compound for PAHs, and the available information on the formation of metabolites and structure of benzo[a]pyrene can theoretically be used to predict potential genotoxicity/carcinogenicity of other PAHs that have not been as extensively studied. 

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