Analysis of the reaction between 2′-deoxycytidine and 4-oxo-2-nonenal by LC/MS revealed the presence of three major products (adducts A1, A2, and B; [M + H]+ = 364). Adducts A1 and A2 were isomeric, and each dehydrated to form adduct B. The structure of adduct B was shown by LC/MS and NMR spectroscopy to be an etheno-2′-deoxycytidine adduct 1′′-[1-(2′-deoxy-βD-erythro-pentofuranosyl)-1H- imidazo[2,1-c]pyrimidin-2-oxo-4-yl]heptane-2′′-one. A time course experiment performed at 65 °C (pH 5-8) showed that the transformation of both A1 and A2 was pH-dependent. In acidic conditions, adducts A1 and A2 dehydrated primarily to adduct B. In contrast, in basic conditions, adducts A1 and A2 hydrolyzed primarily to dCyd. The data are consistent with adducts A1 and A2 being substituted ethano adducts that dehydrate to adduct B, a substituted 3,N4-etheno-2′-deoxycytidine adduct.
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