ELECTROCHEMICAL-BEHAVIOR AND ANTIOXIDANT ACTIVITY OF SOME NATURAL POLYPHENOLS

A number of natural polyphenols (chlorogenic acid (9), cordigol (11), cordigone (12), danthrone (1), 1,5-dihydroxy-3-methoxyxanthone (2), er iosematin (7), flemichin D (8), frutinone A (6), mangiferin (4), querc etin (5), 1,3,6,7-tetrahydroxyxanthone (3) and verbascoside (10)) were investigated for their redox properties using cyclic voltammetry. The antioxidant properties of these compounds were also examined in two m odels, namely lipid peroxidation in rat synaptosomes and AAPH-mediated oxidation of serum albumin. Compounds with a catechol group (9, 4, 5, 3 and 10) were oxidized below 0.4 V and inhibited lipid peroxidation with IC50 values between 2 and 8 mu M. Compounds having one or more is olated phenolic groups and showing an oxidation potential between 0.45 and 0.8 V (11, 12 and 8) inhibited lipid peroxidation with IC50 betwe en 7 and 9 mu M, except 2 (0.45 V), danthrone (0.96 V) and eriosematin which showed no or modest antioxidant activity. Some of the investiga ted compounds also protected albumin from oxidation, but no structure- activity relationship was apparent, suggesting that other factors besi de redox potential influence this activity.