Photochemical Behavior of 6-Methylpterin in Aqueous Solutions: Generation of Reactive Oxygen Species¶

et al. 2006

Helvetica Chimica Acta

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The photochemistry of 6-(hydroxymethyl)pterin (HPT; 1) in aqueous solution (pH 5 -6) was investigated by irradiation at 350 nm at room temperature. The photochemical reactions of the acidic form 1a were followed by UV/VIS spectrophotometry, thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), and enzymatic methods for the determination of the superoxide anion radical (O À 2 ) and hydrogen peroxide (H 2 O 2 ). When 1a is exposed to UV-A radiation, the intermediates 4 and 4' are formed reacting with O 2 to yield 6-formylpterin (FPT; 5) and 6-carboxypterin (CPT; 6) under formation of O À 2 and H 2 O 2 (Scheme 3). The quantum yields of the disappearance of HPT (1a) and of the formation of the photoproducts 5 and 6 were determined. HPT was investigated for its efficiency in singlet-oxygen (

Section: à3mentioning

confidence: 80%

“…of 1a (Fig. 3) The generation of H 2 O 2 during the photooxidation of other pterin derivatives (biopterin, sepiapterin, FPT, 6-methylpterin, pterin) was previously reported [13] [18] [42]. The basic form of HPT (1a) also produces H 2 O 2 under UV-A irradiation [43] in the presence of O 2 .…”

mentioning

confidence: 70%

Photoinduced Formation of Reactive Oxygen Species from the Acid Form of 6‐(Hydroxymethyl)pterin in Aqueous Solution

Thomas

Cabrerizo

et al. 2006

Helvetica Chimica Acta

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“…Recent systematic studies of the production of 1 O 2 by oxidized and reduced pterins in aqueous solution revealed that the oxidation state of the pterin derivative, the nature of the 6-substituent on the pterin moiety, as well as the pH, considerably affect the quantum yields of 1 O 2 production (Φ Δ ) [23][24][25][26]. In these studies, Φ Δ values ( Table 2) were determined by analysis of the weak 1 O 2 NIR phosphorescence at 1270 nm, produced upon excitation of the pterins with UV-A radiation, as described in, e.g., [23,26,27].…”

Section: Production Of Singlet Oxygen By Pterin Derivativesmentioning

confidence: 99%

“…OLIVEROS et al Table 2 Quantum yields of 1 O 2 production (Φ Δ ) by pterin derivatives, rate constants of 1 O 2 total quenching (k t = k r + k q ), physical quenching (k q ) and rate constants of the chemical reaction with 1 O 2 (k r ) in air-equilibrated aqueous solutions (data from refs. [23][24][25][26]28] …”

Section: Production Of Singlet Oxygen By Pterin Derivativesmentioning

confidence: 99%

“…The efficiencies of these processes may be evaluated by determining the rate constants of 1 O 2 physical quenching and of the chemical reaction with 1 O 2 (k q and k r , reactions 6 and 7, respectively). Values of these rate constants have been published for aromatic conjugated and unconjugated pterins, as well as for 7,8-dihydropterins, in aqueous solutions [23][24][25]28,32] (Table 2). Oxidation products have also been investigated to evaluate potential consequences in vivo.…”

Section: Reactivity Of Pterin Derivatives With Singlet Oxygenmentioning

confidence: 99%

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Production and quenching of reactive oxygen species by pterin derivatives, an intriguing class of biomolecules

Oliveros

Dántola

Pure and Applied Chemistry

et al. 2010

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Pterins, a family of heterocyclic compounds derived from 2-aminopteridin-4(1H)-one, are widespread in living systems and participate in important biological functions, such as metabolic redox processes. Under UV-A excitation (320-400 nm), aromatic pterins (Pt) can generate reactive oxygen species (ROS), as a consequence of both energy-and electrontransfer processes from their triplet excited state. Quantum yields of singlet oxygen ( 1 O 2 ) production depend largely on the nature of the substituents on the pterin moiety and on the pH. Formation of the superoxide anion by electron transfer between the pterin radical anion and molecular oxygen leads to the production of significant amounts of hydrogen peroxide (H 2 O 2 ) by disproportionation. Dihydropterins (H 2 Pt) do not produce 1 O 2 but are oxidized by this species with high rate constants yielding pterins as well as H 2 O 2 . In contrast to aromatic derivatives, H 2 Pt are oxidized by H 2 O 2 , and rates and products strongly depend on the nature of the substituents on the H 2 Pt moiety. Aromatic pterins have been found in vivo under pathological conditions, e.g., biopterin or 6-carboxypterin are present in the skin of patients affected by vitiligo, a depigmentation disorder. The biomedical implications of the production of ROS by pterin derivatives and their reactivity with these species are discussed.

Stability of 7,8‐Dihydropterins in Air‐Equilibrated Aqueous Solutions

Dántola

Capparelli

et al. 2008

Helvetica Chimica Acta

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6-Substituted 7,8-dihydropterins (¼ 2-amino-7,8-dihydropteridin-4(1H)-ones) are heterocyclic compounds that occur in a wide range of living systems and participate in relevant biological functions. In airequilibrated aqueous solutions, these compounds react with dissolved O 2 (autooxidation). The rates of these reactions as well as the products formed strongly depend on the chemical structure of the substituents. 7,8-Dihydro-6-methylpterin and 7,8-dihydro-6,7-dimethylpterin that bear electron-donor groups as substituents are the most reactive derivatives and undergo oxidation of the pterin moiety to yield the corresponding oxidized derivatives (6-methylpterin and 6,7-dimethylpterin, resp.). The oxidations of 7,8-dihydrobiopterin, 7,8-dihydroneopterin, and 7,8-dihydrofolic acid are slower, and they yield 7,8-dihydroxanthopterin as the main product. 7,8-Dihydroxanthopterin, 6-formyl-7,8-dihydropterin, and sepiapterin are rather stable, and their consumption in air-equilibrated solutions is negligible for several days. The pseudo-first-order rate constants of the reactions between these compounds and O 2 at 258 and 408 are reported. The biological implications of the results obtained are also discussed.