Generation of 2′-Deoxyadenosine N⁶-Aminyl Radicals from the Photolysis of Phenylhydrazone Derivatives

Abstract

Nitrogen-centered radicals are major species generated by the addition of hydroxyl radicals and the one-electron oxidation of adenine derivatives. Aminyl radicals are also generated in the decomposition of adenine chloramines upon reaction of hypochlorite. Here, we report the photochemistry of modified 2'-deoxyadenosine (dAdo) containing photoactive hydrazone substituents as a model to investigate the chemistry of dAdo N(6)-aminyl radicals. Derivatives of dAdo containing a phenylhydrazone moiety at N6 displayed UV absorption between 300 and 400 nm. Upon UV photolysis in the presence of a H-donor, that is, glutathione, two major products were formed, dAdo and benzaldehyde, indicating efficient homolytic cleavage to dAdo N(6)-aminyl radicals and benzylidene iminyl radicals. dAdo N(6)-phenylhydrazone was photolyzed in the presence of a molar excess of nonmodified dAdo to mimic the reactions taking place in DNA, and the major photoproducts were identified by high-performance liquid chromatography, mass spectrometry, and nuclear magnetic resonance. The formation of 2-(benzylideneamino)-2'-deoxyadenosine as well as a more extensive oxidation product may be explained by the recombination of initial dAdo N(6)-aminyl and benzylidene iminyl radicals. The formation of 2'-deoxyinosine may be explained by hydrolytic deamination of dAdo N(6)-aminyl radicals. Interestingly, a dimeric product containing two dAdo moieties was identified in the photolysis mixture. The present studies demonstrate the ability of dAdo N(6)-aminyl radicals to undergo H-abstraction to give dAdo, deamination to give 2'-deoxyinosine, and addition to the adenine moiety to give dimers.

DNA Base Damage by Reactive Oxygen Species, Oxidizing Agents, and UV Radiation

“…As a model system, the near-UV photolysis of the N6-phenylhydrazone of adenine nucleoside was shown to generate strongly oxidizing Ade-N6-yl radicals in aqueous solution. On the basis of product analysis, the major reaction of Ade-N6-yl radicals involves electron or H-atom abstraction giving back adenine (major reaction), and to a lesser extent, the radicals undergo deamination to inosine and radical addition with DNA bases giving dimeric compounds (Kuttappan-Nair et al 2010). Thus, the low yield of adenine oxidation products may be explained by the regeneration of adenine.…”

One-electron oxidation reactions of purine and pyrimidine bases in cellular DNA

“…Near-UV photolysis of modified dAdo containing a phenylhydrazone moiety at N6 induces homolytic cleavage of the hydrazine to produce dAdo N 6-aminyl radicals and benzylidene iminyl radicals (Kuttappan-Nair et al 2010). The resulting dAdo N 6-aminyl radicals were shown to undergo H-abstraction to give dAdo, deamination to give 2′-deoxyinosine, and addition to dAdo moiety to give dimeric products (Kuttappan-Nair et al 2010).…”

Synthesis and biological activity of novel N6-substituted and 2,N6-disubstituted adenine ribo- and 3′-C-methyl-ribonucleosides as antitumor agents

“…Compounds 12 and 17 required a longer reaction time and higher temperature presumably due to the low reactivity of the used amines. In addition, N 6 -hydroxy-2 0 -deoxyadenosine (18) [16] and N 6 -amino-2 0 -deoxyadenosine (19) [17] were prepared as reported in the literature.…”