Characterization of 2'-deoxyadenosine adducts derived from 4-oxo-2- nonenal, a novel product of lipid peroxidation

Analysis of the reaction between 2'-deoxyadenosine and 4-oxo-2-nonenal by liquid chromatography/mass spectrometry revealed the presence of three major products (adducts A₁, A₁, and B). Adducts A₁ and A₁ were isomeric; they interconverted at room temperature, and they each readily dehydrated to form adduct B. The mass spectral characteristics of adduct B obtained by collision-induced dissociation coupled with multiple tandem mass spectrometry were consistent with those expected for a substituted etheno adduct. The structure of adduct B was shown by NMR spectroscopy to be consistent with the substituted etheno-2'-deoxyadenosine adduct 1''-[3-(2'-deoxy-β-D- erythropentafuranosyl)-3H-imidazo[2,1-i]purin-7-yl]heptane-2''-one. Unequivocal proof of structure came from the reaction of adducts A₁ and A₂ (precursors of adduct B) with sodium borohydride. Adducts A₂ and A₂ each formed the same reduction product, which contained eight additional hydrogen atoms. The mass spectral characteristics of this reduction product established that the exocyclic amino group (N⁶) of 2'-deoxyadenosine was attached to C-1 of the 4-oxo-2-nonenal. The reaction of 4-oxo-2-nonenal with calf thymus DNA was also shown to result in the formation of substituted etheno adducts A₁ and A₁ and substituted etheno adduct B. Adduct B was formed in amounts almost 2 orders of magnitude greater than those of adducts A₁ and A₁. This was in keeping with the observed stability of the adducts. The study presented here has provided additional evidence which shows that 4- oxo-2-nonenal reacts efficiently with DNA to form substituted etheno adducts.