Novel liposoluble spin traps derived from amidinoquinoxaline N-oxides: characterization by ESR

GRACIELA FACORRO; MARÍA B. GARCÍA; LIDIA PIEHL; LILIANA R. ORELLI; EMILIO RUBIN DE CELIS

Montevideo, Uruguay

Congreso; Free radicals in Montevideo 2007; 2007

SFRBM-South American Group

Novel Liposoluble Spin Traps derived from amidinoquinoxaline N-oxides: characterization by ESR.Facorro, Graciela1; García, Beatriz2; Piehl, Lidia1; Orelli, Liliana2 and Rubin de Celis, Emilio1.1 Cátedra de Física, Facultad de Farmacia y Bioquímica. Universidad de Buenos Aires. Argentina.2 Cátedra de Química Orgánica I. Facultad de Farmacia y Bioquímica. Universidad de Buenos Aires. Argentina. Spin trapping is a unique technique that allows the detection of short lived free radicals for direct electron spin resonance (ESR) spectroscopy observation. The spin adducts have a long half-life than the trapped free radicals. Nevertheless, spin adducts are frequently labile. In the present work, a novel series of nitrones was synthesized and their methyl spin adducts were characterized. Eight compounds derived from the 2,3-dihydro-1H-pyrimido[1,2a]quinoxaline 6-oxide with C5-substituents: A: 4-methoxyphenyl, B: phenyl, C: 4-clorophenyl, D: 4-nitrophenyl, E: 2-clorophenyl, F: 2-nitrophenyl, G: methyl and H: benzyl, were studied. Methyl radical was generated using the Fenton reaction in PBS pH 7.6 in the presence of 33% DMSO. The spin trapped adduct signals were followed by recording their ESR spectra in function of time. Novel spin traps were compared with the widely used 5,5-dimethyl-1-pyrroline N-oxide (DMPO). Negative controls were also carried out. All compounds, except F, showed spin trap properties. Spin adducts were characterized spectrally by simulation of the experimental ESR spectra, showing a characteristic ESR spectrum with 9 peaks. All of them were more persistent than the DMPO adduct, presenting different stabilities. The decay of the spin trap adducts followed a pseudo-first order kinetics. Their half-life times were: A=97 min, B=143 min, C=23 min, D=133 min, E=46 min, G=61 min, H=20 min. DMPO in similar experimental conditions, showed a half-life of 9 min. Spin adducts formation kinetics were observed for A, B and D compounds during the first minutes of the Fenton reaction (up to 30-40 minutes). Competition studies with DMPO reveled the persistence of the signal of the novel adducts after DMPO adduct disappear. The trapping efficiencies of the new nitrones, evaluated by normalized double integration, were equivalent or higher than that of the DMPO. The liposolubility and the high stability of some of the novel spin traps might be an advantage for the detection of free radicals in biological systems