Anthraquinone‐Sensitized Photooxidation of 5‐Methylcytosine in DNA Leading to Piperidine‐Induced Efficient Strand Cleavage

Abstract

One-electron photooxidations of 5-methyl-2'-deoxycytidine (d(m)C) and 5-trideuteriomethyl-2'-deoxycytidine ([D(3)]d(m)C) by sensitization with anthraquinone (AQ) derivatives were investigated. Photoirradiation of an aerated aqueous solution containing d(m)C and anthraquinone 2-sulfonate (AQS) afforded 5-formyl-2'-deoxycytidine (d(f)C) and 5-hydroxymethyl-2'-deoxycytidine (d(hm)C) in good yield through an initial one-electron oxidation process. The deuterium isotope effect on the AQS-sensitized photooxidation of d(m)C suggests that the rate-determining step in the photosensitized oxidation of d(m)C involves internal transfer of the C5-hydrogen atom of a d(m)C-tetroxide intermediate to produce d(f)C and d(hm)C. In the case of a 5-methylcytosine ((m)C)-containing duplex DNA with an AQ chromophore that is incorporated into the backbone of the DNA strand so as to be immobilized at a specific position, (m)C underwent efficient direct one-electron oxidation by the photoexcited AQ, which resulted in an exclusive DNA strand cleavage at the target (m)C site upon hot piperidine treatment. In accordance with the suppression of the strand cleavage at 5-trideuterio-methylcytosine observed in a similar AQ photosensitization, it is suggested that deprotonation at the C5-methyl group of an intermediate (m)C radical cation may occur as a key elementary reaction in the photooxidative strand cleavage at the (m)C site. Incorporation of an AQ sensitizer into the interior of a strand of the duplex enhanced the one-electron photooxidation of (m)C, presumably because of an increased intersystem crossing efficiency that may lead to efficient piperidine-induced strand cleavage at an (m)C site in a DNA duplex.

Current Developments in the Syntheses of 1,2,4-Triazole Compounds

“…Experiments showed that compound 196 could be successfully transformed into the deoxyuridine derived triazole 197 in yield of 72% via N-arylation with 1,2,4-triazole in the presence of phosphorus oxychloride and triethylamine, and compound 197 could be oxidated to give compounds with efficient strand cleavage in a DNA duplex (Scheme 85). This synthetic method provides useful strategy for the preparation of deoxyuridines containing triazole derivatives in good yields [270].…”

DNA damage photo-induced by chloroharmine isomers: hydrolysisversusoxidation of nucleobases

“…It is well-known that the reactivity of pyrimidine bases with most ROS including singlet oxygen, superoxide anion radical and hydrogen peroxide, at the exception however of hydroxyl radical (HO • ) is quite inefficient 41 . In addition to HO • -mediated reactions, pyrimidine bases can be part of one-electron photosensitized oxidative reactions, as it was demonstrated for the epigenetic modification 5-methyl-2'-deoxycytidine 42,43 . Therefore, results…”