| Abstract
| - In this work, the pro-oxidant behavior of oleuropein (OLP, 1) is characterized in a Fenton-likeexperiment by means of ESR spectroscopy using the spin trap system DMSO and 4-(pyridyl-1-oxide)-N-tert-butyl nitrone (POBN) in phosphate buffer (PB) solution. Ferrous ions in the absence of hydrogenperoxide cause the formation of the stable nitroxide species 4 and 5 through the intermediate perferrylspecies. OLP displays its antioxidant activity in vitro blocking the oxidation path that leads to methoxylradicals hence to the formation of the stable radical species 5. The role of the catechol moiety wasproved when the perferryl experiments were repeated in the presence of the dimethylated oleuropeinhomologue (OLP-Met2, 2). The dual behavior of oleuropein, similar to that ascertained for othercatechol and non-catechol natural active species, should provide warnings for its use as nutraceuticalor as drug with manifold healing effects. Keywords: Oleuropein; pro-oxidant activity; ESR; spin trapping; catechols; iron complexes
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