Characterization and reactivity of photodimers of dihydroneopterin and dihydrobiopterin

MARIANA VIGNONI; CAROLINA LORENTE; FRANCO M. CABRERIZO; ROSA ERRA-BALSELLS; ESTHER OLIVEROS; ANDRÉS H. THOMAS

Photochemical and Photobiological Sciences

ROYAL SOC CHEMISTRY

Lugar: CAMBRIDGE; Año: 2012 vol. 11 p. 979 - 987

1474-905X

7,8-Dihydrobiopterin (H2Bip) and 7,8-dihydroneopterin (H2Nep) belong to a class of heterocyclic compounds present in a wide range of living systems. H2Bip accumulates in the skin of patients suffering from vitiligo, whereas H2Nep is secreted by human macrophages when the cellular immune system is activated. We have investigated the [2+2]-photodimerization of both compounds upon UV-A irradiation (320–400 nm) and the thermal stability of the corresponding dimers. The study was performed in neutral aqueous solutions. The reactions were followed by UV/Visible spectrophotometry and HPLC and the products were analyzed by means of electrospray ionization mass spectrometry and 1H NMR. Excitation of H2Bip and H2Nep leads to the formation, in each case, of at least two isomeric dimers with molecular masses equal to exactly twice the molecular mass of the reactant. The dimers undergo a thermal process that may consist in a retro [2+2]-cycloaddition and hydrolysis to yield the reactant (H2Bip or H2Nep) and a product that has incorporated a molecule of H2O.