Free radical scavenging and antioxidative activities of caffeic acid phenethyl ester (CAPE) and its related compounds in solution and membranes: A structure–activity insight

Caffeic acid phenethyl ester (CAPE) together with caffeic acid, ferulic acid and ethyl ferulate are constituents of propolis and structurally related, which allowed us to gather important information regarding the structure–activity relationships underlying the biological activity of such compounds. In this work, we have investigated the direct scavenging effects of the antioxidants on 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals, galvinoxyl radicals and superoxide anions (O2-), as well as the anti-lipoperoxidative capacity on human erythrocytes hemolysis and rat liver microsomal membranes peroxidation induced in vitro by two different sources of free radicals: 2,2′-azobis(2-amidinopropane) (AAPH) and Fe2+/ascorbate (OH). The results established that the radical scavenging activity of the compounds increased with increasing numbers of hydroxyl groups or catechol moieties in the molecule, while in the biomembrane systems, the antioxidative activity of the test compounds depends not only on the hydroxyl groups or catechol rings but also on the polarity and hydrophobicity of the antioxidants. In addition, CAPE is the most effective antioxidant of the compounds we tested in our in vitro systems.