1H,13C and15N nuclear magnetic resonance analysis and chemical features of the two main radical oxidation products of 2′-deoxyguanosine: oxazolone and imidazolone nucleosides

Abstract

The two primary one-electron oxidation and ˙OH-mediated decomposition products of 2′-deoxyguanosine 1 are 2,2-diamino-4-[(2-deoxy-β-D-erythro-pentofuranosyl)amino]-2,5-dihydrooxazol-5-one 3 (dZ) and its precursor, 2-amino-5-[(2-deoxy-β-D-erythro-pentofuranosyl)amino]-4H-imidazol-4-one 2 (dIz). Here, we describe in detail the spectroscopic and chemical properties of both oxidative DNA lesions. The structures for dZ 3 and dIz 2 were determined by fast-atom bombardment mass spectrometry, UV spectroscopy, IR spectroscopy, together with ¹H, ¹³C, ¹⁵N and ¹⁷O 1D and 2D NMR spectroscopy. In neutral aqueous solution dIz 2 is hydrolysed to dZ 3 (t_½= 147 min at 37 °C) with the incorporation of one molecule of water. Hot alkali treatment (65 °C; pH 13) of dIz 2 and dZ 3 quantitatively results in the release of guanidine (t_½= 3.3 and 3.1 min, respectively). The latter property allowed us to develop a specific and sensitive method for the detection of the two modified nucleosides 2 and 3. Methoxyamine reacts quantitatively with 3′,5′-di-O-acetyl-dIz 2a 120-times faster than with 3′,5′-di-O-acetyl-dZ 3a to form four 3,5-di-O-acetyl-2-deoxy-D-erythro-pentose–methoxyamine isomers.