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Singlet Oxygen Oxidation of Isolated and Cellular DNA: Product Formation and Mechanistic Insights
Author(s) -
Cadet Jean,
Ravanat JeanLuc,
Martinez Glaucia R.,
Medeiros Marisa H. G.,
Mascio Paolo Dl
Publication year - 2006
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1562/2006-06-09-ir-914
Subject(s) - chemistry , singlet oxygen , moiety , photochemistry , dna , dna damage , aqueous solution , reactive intermediate , molecule , decomposition , guanine , singlet state , dna oxidation , solvent , oxygen , stereochemistry , organic chemistry , biochemistry , catalysis , excited state , nucleotide , physics , nuclear physics , gene
This survey focuses on recent aspects of the singlet oxygen oxidation of the guanine moiety of nucleosides, oligonucleotides, isolated and cellular DNA that has been shown to be the exclusive DNA target for this biologically relevant photo‐generated oxidant. A large body of mechanistic data is now available from studies performed on nucleosides in both aprotic solvents and aqueous solutions. A common process to both reaction conditions is the formation of 8‐oxo‐7,8‐dihydroguanine by reduction of 8‐hydroperoxyguanine that arises from the rearrangement of initially formed endoperoxide across the 4,8‐bond of the purine moiety. However, in organic solvent the hydroperoxide is converted as a major degradation pathway into a dioxirane that subsequently decomposes into a complex pattern of oxidation products. A different reaction that involved the formation of a highly reactive quinonoid intermediate consecutively to the loss of a water molecule from the 8‐hydroperoxide has been shown to occur in aqueous solution. Subsequent addition of a water molecule at C5 leads to the generation of a spiroiminodihydantoin compound via a rearrangement that involves an acyl shift. However, in both isolated and cellular DNA the latter decomposition pathway is at the best a minor process, because only 8‐oxo‐7,8‐dihydroguanine has been found to be generated. It is interesting to point out that singlet oxygen has been shown to contribute predominantly to the formation of 8‐oxo‐7,8‐dihydroguanine in the DNA of bacterial and human cells upon exposure to UVA radiation. It may be added that the formation of secondary singlet‐oxygen oxidation products of 8‐oxo‐7,8‐dihydroguanine, including spiroiminodihydantoin and oxaluric acid that were characterized in nucleosides and oligonucleotide, respectively, have not yet been found in cellular DNA.