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• 88847-89-6 7,8-dihydro-8-oxo-2'-deoxyguanosine 
• 961-07-9 2'-Deoxyguanosine 

Relevant academic research and scientific papers

Photooxiation of 8-oxo-7,8-dihydro-2'-deoxyguanosine by thermally generated triplet-excited ketones from 3-(hydroxymethyl)-3,4,4-trimethyl-1,2-dioxetane and comparison with type I and type II photosensitizers

Calf thymus DNA and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) were photooxidized in the dark by triplet-excited ketones generated in the thermal decomposition of 3-(hydroxymethyl)-3,4,4-trimethyl-1,2-dioxetane (HTMD). The oxidation of DNA led to 8-oxodGuo and the type I photooxidation product 2,2-diamino[2-deoxy-β-D-erythro-pentofuranosyl)-4-amino]-5(2H)-oxazol one (oxazolone). While the yield of oxazolone progressively increased, 8-oxodGuo was substantially consumed in DNA on successive exposure to HTMD. The oxidation of authentic 8-oxodGuo by HTMD and established photosensitizers such as benzophenone (mainly type I) and Rose Bengal (predominantly type II) was studied in detail in regard to the concentration and time dependence and the influence of D2O versus H2O. The singlet-oxygen-derived 4R* and 4S* diastereomers of 4-hydroxy-8-oxo-4,8-dihydro-2'-deoxyguanosine (4-HO-8-oxodGuo) and oxazolone were the major products. A substantial kinetic D2O effect (ca. 10-fold) in the Rose Bengal-photosensitized degradation of 8-oxodGuo unequivocally established that in this case singlet oxygen (type II photooxidation) is involved. However, the efficient formation of oxazolone by benzophenone as a characteristic type I photooxidant, as well as in the HTMD-mediated oxidation (predominantly type I), and the fact that these processes exhibit a negligible D2O effect provide cogent experimental evidence for an electron or hydrogen atom transfer mechanism (type I photooxidation) in the oxidative degradation of 8-oxodGuo into oxazolone. The unprecedented observation that comparable product ratios of 4-HO-8-oxodGuo and oxazolone were obtained in the 8-oxodGuo oxidations, irrespective of whether Rose Bengal as a typical type II photooxidant or benzophenone as an established type I photooxidant was employed, is presumably due to electron-transfer chemistry of 1O2 with the easily oxidized 8-oxodGuo in view of its low oxidation potential. This nicely accounts for the fact that the primary oxidation product 8-oxodGuo, which serves as an important monitor of oxidative genotoxicity, may not accumulate appreciably in the photooxidation of DNA.

Photochemistry and photobiology of furocoumarin hydroperoxides derived from imperatorin: Novel intercalating photo-fenton reagents for oxidative DNA modification by hydroxyl radicals

Photochemical and photobiological properties of the imperatorin-derived furocoumarin hydroperoxides 1a, 1a′, 2a and 2a′ have been investigated. Irradiation (350 nm) of the hydroperoxide 2a′ afforded the alcohol 2b (2%), a diastereomeric mixture of the hydroxy epoxide 2c (40%; diastereomeric ratio = 80:20) and the epoxide 2d (8%). The formation of these products was rationalized in terms of homolysis of the hydroperoxide bond initiated by intramolecular energy transfer from the photoexcited furocoumarin chromophore. The quantum yields for the photolytic decomposition of hydroperoxides were estimated to be in the range of 0.03-0.85 and decreased in the order 2a ? 2a′ ? 1a′ ≥ 1a. The involvement of hydroxyl radicals in these reactions was established by trapping experiments with benzene and spectroscopic evidence was obtained by EPR spin trapping with 5,5-dimethylpyrroline-N-oxide. Fluorescence titration, DNA melting and linear dichroism studies of furocoumarins indicated that these compounds undergo efficient complexation and also intercalation into the DNA. The binding parameters K (intrinsic binding constant) and 1/n (frequency of binding sites) of complexes between furocoumarin derivatives and DNA were determined to be in the range of 3900-23900 M-1 and 0.017-0.045. The photoreaction of 1a′ and 1b′ with 2′-deoxyguanosine (dGuo) afforded exclusively 7,8-dihydro-8-oxo-2′-deoxy-guanosine (8-oxodGuo), presumably through singlet oxygen, which was formed in a type II photooxidation process. In contrast, the hydroperoxide 2a oxidized dGuo to oxazolone as major and 8-oxodGuo as minor products through hydroxyl radicals, which were generated from 2a under photolytic conditions. Interestingly, the photoreactions of furocoumarins with salmon testes DNA showed that the highly reactive (φ = 0.85) hydroperoxide 2a is also most efficient in inducing the mutagenic DNA oxidation product 8-oxodGuo. Hence, the novel furocoumarin hydroperoxide 2a constitutes the first intercalating photo-Fenton reagent and serves as convenient hydroxyl radical source for genotoxicity studies.

Reaction of Singlet Oxygen with 2'-Deoxyguanosine and DNA. Isolation and Characterization of the Main Oxidation Products

The reaction of singlet molecular oxygen with 2'-deoxyguanosine and DNA was studied. Emphasis was placed on the identification and characterization of the main methylene blue mediated type II (singlet oxygen) oxidation products of 2'-deoxyguanosine and its corresponding 3',5'-di-O-acetylated derivative. Two major oxidation products of 2'-deoxyguanosine were isolated and characterized by mass spectrometry analysis and extensive 1H and 13C NMR measurements as the two 4R* and 4S* diastereomers of 4,8-dihydro-4-hydroxy-8-oxo-2'-deoxyguanosine. The addition of 1O2 was also found to occur to the base moiety of the corresponding 3',5'-di-O-acetylated derivative. Methylene blue mediated photosensitization of 2'-deoxygunosine led also to the production of 7,8-dihydro-8-oxo-2'-deoxyguanosine, but in a relatively lower yield with respect to the two above diastereomers. The participation of singlet oxygen in the mechanism of formation of these oxidation products was confirmed. A reasonable mechanism involving the transient formation of an unstable endoperoxide produced through a Diels-Alder 1,4-cycloaddition of singlet oxygen to the purine ring is suggested. Quantitative analysis allowed us to demonstrate that the two diastereomers of 4,8-dihydro-4-hydroxy-8-oxo-2'-deoxyguanosine are the main singlet oxygen oxidation products of the guanine moiety within nucleosides, whereas 7,8-dihydro-8-oxoguanine was found to be the major 1O2 oxidation product of guanine in double-stranded DNA.

Mapping structurally defined guanine oxidation products along DNA duplexes: Influence of local sequence context and endogenous cytosine methylation

DNA oxidation by reactive oxygen species is nonrandom, potentially leading to accumulation of nucleobase damage and mutations at specific sites within the genome. We now present the first quantitative data for sequence-dependent formation of structurally defined oxidative nucleobase adducts along p53 gene-derived DNA duplexes using a novel isotope labeling-based approach. Our results reveal that local nucleobase sequence context differentially alters the yields of 2,2,4-triamino-2H-oxal-5-one (Z) and 8-oxo-7,8-dihydro-2′- deoxyguanosine (OG) in double stranded DNA. While both lesions are overproduced within endogenously methylated MeCG dinucleotides and at 5′ Gs in runs of several guanines, the formation of Z (but not OG) is strongly preferred at solvent-exposed guanine nucleobases at duplex ends. Targeted oxidation of MeCG sequences may be caused by a lowered ionization potential of guanine bases paired with MeC and the preferential intercalation of riboflavin photosensitizer adjacent to MeC:G base pairs. Importantly, some of the most frequently oxidized positions coincide with the known p53 lung cancer mutational hotspots at codons 245 (GGC), 248 (CGG), and 158 (CGC) respectively, supporting a possible role of oxidative degradation of DNA in the initiation of lung cancer.

Hydroxyl radical-induced degradation of 2′-deoxyguanosine under reducing conditions

Addition of hydroxyl radical to the base moiety of 2′-deoxyguanosine (dGuo) leads to the formation of two main radicals exhibiting oxidising and reducing properties, respectively. The oxidising radical reacts with oxygen to yield 2,2-diamino-5-[2-deoxy-β-D-erythro-pentofuranosyl)amino]oxazol-5(2H)-one (oxazolone) as the final product. The reducing radical is either preferentially oxidised into 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodGuo) or reduced into a 2,6-diamino-4-hydroxy-5-formamidopyrimidine derivative (FapydGuo) depending on conditions. We report here that the presence of reducing compounds (ascorbate or cysteine) strongly modifies the distribution of modified nucleosides upon γ irradiation of an aerated aqueous solution of dGuo. The yield of oxazolone decreases while that of 8-oxodGuo and FapydGuo increases. This was explained by the reduction of the oxidising radical which prevents the occurrence of the restitution of dGuo through a reaction between the oxidising and the reducing purine radicals. The study was extended to the decomposition of dGuo upon photochemical release of .OH by N-hydroxypyrimidine-2-thione (HPT). The analysis of the base modification products of dGuo induced by the latter system showed that HPT exhibits reducing properties and cannot be used as a pure photochemical source of ?OH radical.

Type II guanine oxidation photoinduced by the antibacterial fluoroquinolone rufloxacin in isolated DNA and in 2′-deoxyguanosine

The role played by type I (radical) and type II (singlet oxygen) mechanisms in the Rufloxacin (RFX)-photoinduced production of 8-hydroxy-2′-deoxyguanosine in DNA has been evaluated. This fluoroquinolone drug has been shown to be able to photoinduce increased levels of some DNA base oxidation products, such as 8-OH-dGuo, that are indicative of mutagenic and carcinogenic events, with probable implications in aging processes. The relative weight of the two photosensitization mechanisms was obtained via determination of two different photoproducts of 2′-deoxyguanosine (dGuo), which are diagnostic of the two different pathways, namely, (4R*)- and (4S*)-4,8-dihydro-4-hydroxy-8-oxo-2′-deoxyguanosine and 2,2-diamino-4-[(2-deoxy-β-D-erythro-pentofuranosyl)amino]-2, 5-dihydrooxazol-5-one. The observed predominance of type II reaction is in agreement with the fact that the triplet state of RFX is able to transfer with high efficiency its energy to molecular oxygen, giving rise to singlet oxygen. Photophysical measurements suggest that hydrated electrons produced by Rufloxacin photoionization react with dGuo, Thd, and DNA, whereas these biomolecules quench the RFX triplet state with low efficiency. Static quenching of Rufloxacin fluorescence indicates an interaction of this drug both with DNA and with dGuo. On the basis of these experimental data, Rufloxacin photosensitization of DNA is proposed to occur by a type II mechanism.

Identification of the α and β anomers of 1-(2-deoxy-D-erythro- pentofuranosyl)-oxaluric acid at the site of riboflavin-mediated photooxidation of guanine in 2′-deoxyguanosine and thymidylyl-3′-5′- deoxyguanosine

Products of riboflavin-mediated photosensitization of 2′- deoxyguanosine (dG) and thymidylyl-(3′-5′)-2′-deoxyguanosine (TpdG) by 350-nm light in oxygen-saturated aqueous solution have been isolated and identified as 1-(2-deoxy-β-erythro-pentofuranosyl) oxaluric acid (β-dOx) and thymidylyl-(3′-5′)-1-(2-deoxy-β-D-erythro- pentofuranosyl) oxaluric acid (Tpβ-dOx), respectively. In aqueous solution the modified β-deoxyribonucleoside is slowly converted to the α-anomer, generating α-dOx and Tpα-dOx. These modified nucleosides and dinucleoside monophosphates have been isolated by HPLC and characterized by proton and carbon NMR spectroscopy, fast atom bombardment mass spectrometry, and enzymatic analyses. Both α-dOx and Tpα-dOx slowly convert back into the modified β-deoxyribonucleoside, indicating that the furanosidic anomers are in dynamic equilibrium. Relative to TpdG, the rate of hydrolysis of Tpβ-dOx and Tpα-dOx by spleen phosphodiesterase is greatly reduced. Hot piperidine (1.0 M, 90°C, 30 min) destroys Tpβ-dOx and Tpα-dOx. Riboflavin-mediated photosensitization of TpdG in D 2O instead of H2O has no detectable effect on the yield of Tpβ-dOx, suggesting that oxaluric acid is generated through a Type-I reaction mechanism, likely through the intermediary on initially generated 8-oxo-7,8-dihydro-2′-deoxyguanosine.

Formation of a diimino-imidazole nucleoside from 2′-deoxyguanosine by singlet oxygen generated by methylene blue photooxidation

Singlet oxygen (1O2) is capable of inducing genotoxic, carcinogenic and mutagenic effects. It has previously been reported that the reaction of 1O2 with 2′-deoxyguanosine, which is a major target of 1O2 among the DNA constituents, leads to formation of various oxidized products including 8-oxo-7,8-dihydro-2′-deoxyguanosine and spiroiminodihydantoin, amino-imidazolone and diamino-oxazolone nucleosides. In addition to these products, we report that a novel diimino-imidazole nucleoside, 2,5-diimino-4-[(2-deoxy-β-D-erythro-pentofuranosyl)amino]-2H,5H- imidazole (dD), is formed by reaction of 2′-deoxyguanosine with 1O2 generated by irradiation with visible light in the presence of methylene blue under aerobic conditions. Its identification is based on identical chromatographic and spectroscopic data with an authentic compound, which we recently isolated and characterised from the reaction mixture of 2′-deoxyguanosine with reagent HOCl and a myeloperoxidase-H2O2-Cl- system. The yield of dD was increased by D2O and decreased by azide. dD was not generated from 8-oxo-7,8-dihydro-2′-deoxyguanosine. These results indicate that dD is generated by 1O2 directly from 2′-deoxyguanosine, but not via 8-oxo-7,8-dihydro-2′-deoxyguanosine. dD may play a role in the genotoxicity of singlet oxygen in cells.

Oxidative DNA damage by radicals generated in the thermolysis of hydroxymethyl-substituted 1,2-dioxetanes through the α cleavage of chemiexcited ketones

The 3-(hydroxymethyl)-3,4,4-trimethyl-1,2-dioxetane (HTMD) highly efficiently damages DNA compared to the merely alkyl-substituted derivative 3,3,4,4-tetramethyl-1,2-dioxetane (TMD). To elucidate this difference in oxidative reactivity, two additional hydroxymethyl-substituted 1,2- dioxetanes, namely cis/trans-3-(hydroxymethyl)-3,4-dimethyl-4-(phenylmethyl)- (lα/1β) and 3-(hydroxymethyl)-4,4-dimethyl-3(phenylmethyl)-1,2-dioxetane (2), were investigated in regard to their photochemical and photobiological properties. The high genotoxic effects of the hydroxymethyl-substituted 1,2- dioxetanes, which are reflected in the significant formation of single- strand breaks in plasmid pBR 322 DNA and the efficient oxidation of guanine in calf thymus DNA and the nucleoside 2'-deoxyguanosine (dGuo), are for the first time understood in terms of radical chemistry. The reactivity order of the dioxetanes 1α/1β > HTMD > 2 >> TMD to damage DNA parallels the propensity of these dioxetanes to generate radicals. These reactive species are formed in the thermolysis of the dioxetanes through α cleavage of the intermediary triplet-excited α-hydroxy- and α-phenyl-substituted carbonyl products. The presence of radicals was confirmed by spin-trapping experiments with 5,5-dimethyl-1-pyrroline N-oxide and by laser-flash photolysis. These carbon-centered radicals are efficiently scavenged by molecular oxygen to produce peroxyl radicals, which are proposed as the active DNA damaging species in the thermal decomposition of the hydroxymethyl-substituted 1,2- dioxetanes HTMD, 1α/1β, and 2.

Type I and type II photosensitized oxidative modification of 2'-deoxyguanosine (dGuo) by triplet-exicted ketones generated thermally from the 1,2-dioxetane HTMD

The nucleoside 2'-deoxyguanosine (dGuo) was treated with 3-(hydroxymethyl)-3,4,4-trimethyl-1,2-dioxetane (HTMD), the latter generates efficiently triplet-excited carbonyl products on thermal decomposition in the dark. The type I photooxidation products, 2,2-diamino-[(2-deoxy-β-D-erythro-pentofuranosyl)-4-amino]-5(2H)-oxaz olone (oxazolone) and the cyclic nucleoside 2-(S)-2,5'-anhydro-1-(2-deoxy-β-D-erythro-pentofuranosyl)-5-guanidiny lidene-2-hydroxy-4-oxoimidazolidine (oxoimidazolidine), as well as the type II photooxidation products 4-(R)*- and 4-(S)*-4-hydroxy-8-oxo-4,8-dihydro-2'-deoxyguanosine (4-HO-8-oxodGuo) and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo), were quantitatively determined by appropriate selective and sensitive HPLC assays. The concentration and time profiles revealed that about 40% of the triplet ketones derived from the thermal decomposition of HTMD led to photooxidation of dGuo. Essentially equal amounts of type I and type II photooxidation products were found, as could be established by comparison with predominant type I (benzophenone, riboflavin) and type II (Rose Bengal, methylene blue) photosensitizers. The participation of singlet oxygen (type II activity) was confirmed by the substantial D2O effect in the formation of 8-oxodGuo. The results demonstrate that dioxetanes, particularly HTMD, are efficient photooxidants of dGuo on thermal activation in the dark and constitute excellent chemical tools to study photobiological processes without the use of light, in the present case, photogenotoxicity.