Synthesis and Evaluation of New Nitrone-Based Benzoxazinic Antioxidants

Abstract

Oxidative stress is often the cause of a wide range of human chronic pathologies including, but not limited to, stroke and cardiovascular and neurodegenerative diseases. In this setting, increasing efforts are currently being devoted to the design and synthesis of new derivatives with enhanced antioxidant efficacy. Among all the potential molecules of interest, synthetic nitrone spin-traps have attracted a great deal of research attention, particularly due to their dual function as effective inhibitors of oxidative stress and damage and as analytical tools for the detection and characterization of free radicals by means of the electron paramagnetic resonance (EPR) spectroscopy spin trapping technique. In this study, two derivatives of benzoxazinic nitrones (3-aryl-2H-benzo[1,4]oxazin-N-oxides) bearing an electron-withdrawing methyl-acetate group on the benzo moiety (in para and meta positions with respect to the nitronyl function) were synthesized. Their in vitro antioxidant activity was evaluated by means of the α,α-diphenyl-β-picrylhydrazyl radical (DPPH) scavenging assay, and their inhibitory effects on the erythrocyte hemolysis induced by the water-soluble free radical initiator 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH) compared. In addition, EPR was employed to monitor the decay profiles of DPPH to evaluate the kinetic behavior of the different antioxidants tested. Results showed that the presence and the position of the electron-withdrawing methyl-acetate group strongly affects the radical scavenging activity of nitrones. In particular, the newly synthesized para-substituted derivative, when compared to both the meta-substituted isomer and the unsubstituted parent compound, acts as a more effective antioxidant both in cell and cell-free systems. Overall, these results clearly show that the introduction of an electron-withdrawing group on the phenyl moiety significantly increased the antioxidant capacity of benzoxazinic nitrones, thus showing exciting opportunities in the search for new therapeutic agents in the treatment of diseases associated with oxidative stress.