4-hydroxycinnamic ethyl ester derivatives and related dehydrodimers: Relationship between oxidation potential and protective effects against oxidation of low-density lipoproteins.

The electrochemical oxidation potential of a series of monomeric and dimeric 4-hydroxycinnamic ethyl ester derivatives has been compared with their antioxidant activity toward copper-catalyzed human low-density lipoproteins (LDL) oxidation. Within the series of monomeric hydroxycinnamate derivatives, both oxidation potential and IC50 values decreased in the following order: sinapate > ferulate > p-coumarate. Among the 4-hydroxycinnamate dehydrodimer derivatives, noncyclized 8-8 diphenol dehydrodimers followed the same aforementioned sequence order and were found to be better antioxidants than their monomer counterparts. A good correlation between the inhibitory concentration and the oxidation potential was established among all these derivatives. However, a significantly deviating behavior was observed with the 8-5 dihydrobenzofuran and the 8-8 dihydronaphthol cyclic dehydrodimers, which showed lower activities toward copper-catalyzed human LDL, although their oxidation potentials remained very close to those of the noncyclized 8-8 dehydrodimers. Conversely, in the Trolox equivalent antioxidant capacity (TEAC) assay system, the 8-8 dihydronaphthol dehydrodimers were found to be the most efficient free-radical scavengers. Finally, in the series of dehydrodimers studied, it could be concluded that, whatever the in vitro test system used, (a) all dehydrodimer derivatives tested could contribute efficiently to the overall intake of antioxidants in the diet and (b) a low oxidation potential value was in favor of a satisfactory antioxidant activity.