RESUMO
It is now well established that oxidation of 2'-deoxyguanosine (dGuo) in DNA by singlet molecular oxygen [O2 (1Delta(g))] produces 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo), whereas the main degradation products of free dGuo in aqueous solution have been identified as the two diastereomers of spiroiminodihydantoin nucleoside. Interestingly, O2 (1Delta(g))-mediated oxidation of free 8-oxodGuo gives rise to a pattern of degradation products that is different from that observed when the nucleoside is inserted into DNA. The reasons for these differences and the mechanisms involved in the oxidation reactions are not yet completely understood for either dGuo or 8-oxodGuo, either free or within DNA. In the present work, we report a study of the reaction of O2 (1Delta(g)) toward a modified nucleoside, 8-methoxy-2'-deoxyguanosine (8-MeOdGuo), either free or incorporated into an oligonucleotide. The reason for the choice of 8-MeOdGuo as a chemical model to study in more detail the oxidation pathways of 8-oxodGuo or, more precisely, of the tautomeric 8-hydroxy-2'-deoxyguanosine was dictated by the fact that only the 7,8-enolic tautomer is present in the molecule. The thermolysis of an endoperoxide of a naphthalene derivative as a clean chemical source of 18O-labeled O2 (1Delta(g)) was used to oxidize 8-MeOdGuo. The main O2 (1Delta(g)) oxidation products that were separated and analyzed by HPLC coupled to tandem mass spectrometry were identified as the 2'-deoxyribonucleoside derivatives of 2,2,4-triamino-5-(2H)oxazolone, 2,5-diamino-4H-imidazol-4-one together with the methyl-substituted derivatives of spiroiminodihydantoin, oxidized iminoallantoin and urea. On the other hand, O2 (1Delta(g)) oxidation of 8-MeOdGuo-containing oligonucleotide generated imidazolone as the predominant degradation product. These results provided new mechanistic insights into the reactions of O2 (1Delta(g)) with purine nucleosides.
Assuntos
Desoxiguanosina/análogos & derivados , Desoxiguanosina/química , Oxigênio/metabolismo , Cromatografia Líquida de Alta Pressão , DNA/química , Desoxiguanosina/metabolismo , Guanosina/análogos & derivados , Guanosina/química , Temperatura Alta , Espectrometria de Massas , Modelos Químicos , Nucleosídeos/química , Oligonucleotídeos/química , Oxigênio/química , Purinas/química , Oxigênio Singlete , Espectrometria de Massas por Ionização por Electrospray , Compostos de Espiro/química , Fatores de Tempo , Raios Ultravioleta , Ureia/farmacologiaRESUMO
Modified oligonucleotides that contain the hydrophobic 1-hexanol-1,N(6)-etheno-2'-deoxyadenosine adduct have been synthesized using a mild solid phase phosphoramidite chemistry. The presence and the integrity of the modified nucleoside in the synthetic oligomers were confirmed by electrospray ionization and MALDI mass spectrometry measurements together with analysis of the complete enzymatic hydrolysate by high performance liquid chromatography coupled to UV and fluorescent detection techniques.