Distinct Conformers of Alkylchrysenediol Epoxide-Deoxyguanosine Adducts Detected by Proton NMR

Proton NMR spectra, obtained in MeOH-d₄, of the major DNA adduct of 5,7-dimethylchrysene-1,2-diol 3,4-epoxide, identified as 1(R),2(S),3(S)-trihydroxy-4(S)-(N²-deoxyguanosyl)-1,2,3,4-tetrahydro-5,7-dimethylchrysene, showed the presence of two distinct conformers. One conformer, similar to those observed previously in spectra of peracetates of related DNA adducts of anti-diol epoxides of polynuclear aromatic hydrocarbons, had a chair-like conformation of the tetrahydrobenzo ring. The other conformer, which has not been previously observed, had a boat-like conformation of the tetrahydrobenzo ring. This conformer was converted to the chair-like conformer upon addition of D₂O or trifluoroacetic acid to the MeOH-d₄ solutions of the adduct. The new conformers were also observed in proton NMR spectra of major DNA adducts of 5-methylchrysene-and 5,6-dimethylchrysene-1,2-diol 3,4-epoxides.