Novel products generated from 2′-deoxyguanosine by hypochlorous acid or a myeloperoxidase-H₂O₂-Cl-system: Identification of diimino-imidazole and amino-imidazolone nucleosides

Hypochlorous acid (HOCl), generated by myeloperoxidase from H₂O₂ and Cl^-, plays an important role in host defense and inflammatory tissue injury. We report here the identification of products generated from 2′-deoxyguanosine (dGuo) with HOCl. When 1 mM dGuo and 1 mM HOCl were reacted at pH 7.4 and 37°C for 15 min and the reaction was terminated with N-acetylcysteine (N-AcCys), two products were generated in addition to 8-chloro-2′-deoxyguanosine (8-Cl-dGuo). One was identified as an amino-imidazolone nucleoside (dlz), a previously reported product of dGuo with other oxidation systems. The other was identified as a novel diimino-imidazole nucleoside, and 2.4% 8-Cl-dGuo, with 61.5% unreacted dGuo. Precursors of dDiz and dlz containing a chlorine atom were found in the reaction solution in the absence of termination by N-AcCys. dDiz, dlz and 8-Cl-dGuo were also formed from the reaction of dGuo with myeloperoxidase in the presence of H₂O₂ and Cl^- under mildly acidic conditions. These results imply that dDiz and dlz are generated from dGuo via chlorination by electrophilic attack of HOCl and subsequent dechlorination by N-AcCys. These products may play a role in cytotoxic and/or genotoxic effects of HOCl.