Preparation of Quercetin Esters and Their Antioxidant Activity

Quercetin, a polyphenolic compound, is widely distributed in plants and has numerous health benefits. However, its hydrophilicity can compromise its use in lipophilic systems. For this reason, quercetin was esterified with 12 different fatty acids as their acyl chlorides with varying chain lengths and degrees of unsaturation. Two monoesters (Q-3′-O-monoester and Q-3-O-monoester) and four diesters (Q-7,3′-O-diester, Q-3′,4′-O-diester, Q-3,3′-O-diester, and Q-3,4′-O-diester) were the major products as was shown by HPLC-MS and 1H-NMR data. The lipophilicity of quercetin derivatives was calculated; this was found to increase with fatty acid chain length. The antioxidant potential of quercetin and its derivatives was evaluated by using DPPH radical and ABTS radical cation scavenging activity; quercetin showed the highest radical scavenging activity among all tested samples. Despite the decrease of antioxidant activity in this study, the derivatives may show better antioxidant activity in lipophilic media and display improved absorption and bioavailability in the body once consumed.