Degradation mechanism of nucleotides photosensitized by pterin

MARIANA PAULA SERRANO; CAROLINA LORENTE; SANDRA ESTÉBANEZ; CLAUDIO D. BORSARELLI; ANDRÉS H. THOMAS

Santiago de Chile

Congreso; 25st Inter American Photochemical Society Conference (25st I-APS conference); 2016

Inter American Photochemical Society

Pterins belongto a family of heterocyclic compounds present in a wide range of living systemsand participate in relevant biological functions. Under UV-A excitation (320-400nm), pterins can fluoresce, undergo photooxidation and generate reactive oxygenspecies (ROS) [1]. In the presence of oxygen, pterin (Ptr) act asphotosensitizer through type I (electron transfer/H+ abstraction)and/or type II (1O2-singlet oxygen mediated oxidation)mechanisms [2-3]. The photosensitized degradations of purine and pyrimidinenucleotides (dNMP) by Ptr were studied in neutral aqueous solutions upon UV-Airradiation (350 nm) at room temperature, under different experimentalconditions. The photochemical reactions were followed by UV-visspectrophotometry and HPLC, and the photoproducts were analyzed by means ofelectrospray ionization mass spectrometry. Photophysical properties of thetriplet excites states of the sensitizer were characterized using laser flashphotolysis. After analysis of the results, reaction mechanisms were proposed. Underanaerobic conditions, for purine nucleotides, a recombination of the radicalsoccurred, and no consumption of the nucleotide was observed. On the other hand,for pyrimidine nucleotides, the formation of an adduct between the substrateand the sensitizer was observed. The fluorescence properties of the adduct are similarto those of Ptr itself. In the presence of O2, it was observed more initiatedby an electron transfer from the nucleotide to the triplet excited state of thepterin yielding the corresponding pair of radical ions (Pt.- and[C1]  dNMP.+), with the subsequentrecovery of the photosensitizerby electron transfer from Pt.- to O2.Finally, dNMP.+ participates in other reactions to yielddegradation products.consumption of the purine nucleotides than in O2-saturatedsolutions. In this case, there is a competition between different reactionsthat includes type I and type II mechanisms for guanine nucleotide. For theothers nucleotides, which do not react with 1O2, thereaction is    [1] Lorente, C.;et. al.; Acc. Chem. Res. 2006, 39, 395.[2] Petroselli,G.; et. al.; J. Am. Chem. Soc. 2008, 130, 3001.[3] Petroselli, G.; et. al.; Org. Biomol.Chem.2007, 5, 2792.  [C1]Veo mal los símbolos