Spirodi(iminohydantoin) Products from Oxidation of 2′-Deoxyguanosine in the Presence of NH(4)Cl in Nucleoside and Oligodeoxynucleotide Contexts

[Image: see text] Upon oxidation of the heterocyclic ring in 2′-deoxyguanosine (dG), the initial electrophilic intermediate displays a wide range of reactivities with nucleophiles leading to many downstream products. In the present study, the product profiles were mapped when aqueous solutions of dG were allowed to react with NH(4)Cl in the presence of the photooxidants riboflavin and Rose Bengal as well as the diffusible one-electron oxidant Na(2)IrCl(6). Product characterization identified the 2′-deoxyribonucleosides of spiroiminodihydantoin, 5-guanidinohydantoin, and oxazolone resulting from H(2)O as the nucleophile. When NH(3) was the nucleophile, a set of constitutional isomers that are diastereotopic were also observed, giving characteristic masses of dG + 31. ESI(+)-MS/MS of these NH(3) adducts identified them to be spirocycles with substitution of either the C5 or C8 carbonyl with an amine. The NH(3) adducts exhibit acid-catalyzed hydrolysis to spiroiminodihydantoin. Quantification of the NH(3) and H(2)O adducts resulting from oxidation of dG in the nucleoside, single-stranded, and duplex oligodeoxynucleotide contexts were monitored allowing mechanisms for product formation to be proposed. These data also provide a cautionary note to those who purify their oligonucleotide samples with ammonium salts before oxidation because this will lead to unwanted side reactions in which ammonia participates in product formation.