The 5'-aldehyde terminus is a DNA oxidative damage resulting from attack at C5' of 2-deoxyriboses by some potent natural or chemical DNA cleavers. To offer a fast and specific method for characterization of this type of damage, we used on-line electrospray ionization mass spectrometry (ESI-MS) detection during liquid chromatography analyses. The intrinsic reactivity of 5'-aldehyde terminus with nucleophiles (formation of hydrate with water, of a Tris adduct with Tris buffer) or through beta-elimination reaction resulted in complex LC profiles and MS data. We showed that derivatization of the aldehyde function as an oxime ether gives a stable derivative easy to characterize during on-line ESI-MS analyses. Complete structural characterization of the Tris adduct and the oxime ether derivative were obtained from MS and detailed NMR studies performed on derivatized 5'-aldehyde thymidine models.

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