Preparation of resveratrol and quercetin derivatives and their effects on antioxidant and biological activities

Resveratrol and quercetin, two representative polyphenolics found in red wine, onions, and many other sources, have been well documented for having numerous health benefits such as antioxidant, anti-inflammatory, cardioprotective, and anticancer effects. Despite their health-related beneficial properties, their widespread use in lipophilic media such as lipid-based foods and cosmetic formulations is restricted due to their hydrophilicity. Moreover, phenolic compounds, including flavonoids, generally undergo extensive metabolism after consumption, thus they have low bioavailabilities. Even if these compounds can survive from metabolism, they can hardly penetrate lipophilic cell membrane bilayers. One possible solution to this problem is to modify their structures which can be carried out simply as a first approach via esterification. Esterification with fatty acids can enhance lipophilicity that would improve their use in different lipophilic media. Moreover, in the case of esterification with polyunsaturated fatty acids (PUFA), potential health benefits may be enhanced due to the presence of both phenolics and certain healthful PUFA such as those of the omega-3 family. For this reason, fatty acids of different chain length and degree of unsaturation (C3:0-C22:6) were employed as acyl donors. The resveratrol and quercetin derivatives so prepared were evaluated for their antioxidant activities in different systems, such as the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay; the 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radical cation scavenging assay; a bulk oil system; β-carotene bleaching assay; a hydroxyl radical-induced DNA scission assay, and the copper-induced lowdensity lipoprotein (LDL) oxidation assay. Selected resveratrol derivatives were further evaluated for their antioxidant activity and cell viabilities (A431, MCF7, HT-29, and AGS cells). All test compounds showed antioxidant activity in a system-dependent manner. The resveratrol and quercetin derivatives showed a decreased radical scavenging activity compared to their parent molecules. However, some derivatives exhibited a similar and/or a better antioxidant activity than resveratrol and quercetin themselves in different systems, such as in the bulk oil assay and copper-induced low-density lipoprotein (LDL) oxidation assays. In this work, both resveratrol and quercetin derivatives showed potential use in lipophilic systems, therefore they might serve as possible functional food ingredients as well as health promoting supplements