Synthesis, characterization, and conformational analysis of DNA adducts from methylated anilines present in tobacco smoke.

The ability of a series of aromatic amines present in tobacco smoke (2-, 3-, and 4-methylaniline, 2,3- and 2,4-dimethylaniline) to bind to DNA has been investigated by reacting N-(acyloxy)arylamines with dG, dG nucleotides, and DNA. The predominant products from reactions with dG and the nucleotides were characterized as N-(deoxyguanosin-8-yl)arylamines by spectroscopic and HPLC methods. HPLC and spectroscopic analyses of the modified DNA indicated the same adducts. Analyses of the 1H and 13C NMR spectra suggested that the adducts containing a methyl substituent ortho to the arylamine nitrogen had a higher percentage of syn conformers. This observation was supported by theoretical simulation studies that indicated substantial percentages of low energy syn conformers, increasing with the substitution pattern in the order para < meta < ortho < ortho,para < ortho,meta. The results demonstrate that, although single-ring arylamines are considered weak carcinogens, their electrophilic N-acetoxy derivatives, which are plausible metabolic intermediates, react with DNA to yield covalent adducts structurally identical to those derived from carcinogenic polyarylamines, such as 2-aminofluorene and 4-aminobiphenyl. Furthermore, the conformational perturbation induced in DNA by the formation of the monoarylamine-DNA adducts, especially those with an ortho substituent, may contribute to the biological activities of these compounds.