Photophysical and Photochemical Properties of 3-methylpterin as a New and More Stable Pterin-type Photosensitizer

ESTÉBANEZ, SANDRA; LORENTE, CAROLINA; KAUFMAN, TEODORO S.; LARGHI, ENRIQUE L.; THOMAS, ANDRÉS H.; SERRANO, MARIANA P.

PHOTOCHEMISTRY AND PHOTOBIOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2018 vol. 94 p. 881 - 889

0031-8655

Pterin derivatives are heterocyclic compounds whichare present in different biological systems. Neutral aqueous solutions ofpterins present acid?base and keto?enolequilibria. These compounds, under UV-A radiation fluoresce,undergo photooxidation, generate reactive oxygen species and photoinduce theoxidation of biological substrates. As photosensitizers, they may act throughdifferent mechanisms, mainly through an electron transfer-initiated process(type-I mechanism), but they also produce singlet molecular oxygen (1O2) uponirradiation (type-II mechanism). In general, upon UV-A excitation two tripletstates, corresponding to the lactim and lactam tautomers, are formed, but onlythe last one is the responsible for the photosensitized reactions ofbiomolecules. We present a study of the photochemical properties of3-methylpterin (3-Mep) which, in contrast to most pterin derivatives, existsonly in the lactam form. Also an improvement in the synthesis of 3-Mep is reported.The spectroscopic properties 3-Mep in aqueous solution were similar to those ofthe unsubstituted pterin derivative (Ptr) in its acid form, such as absorption,fluorescent and phosphorescent emission spectra. Experimentsusing 20-deoxyguanosine50-monophosphate(dGMP) as oxidizable target demonstrated that methylation at C-3 position ofthe pterin moiety does not affect significantly the efficiency ofphotosensitization, but results in a more photostable sensitizer.