ANTIOXIDANT PROPERTIES OF HYDROXY-FLAVONES

The antioxidant properties of 24 hydroxy-flavones were evaluated. Resu lts show that 2',3',4'-OH substitution on the B ring plays a crucial r ole in radical scavenger activity in the DPPH assay and in the inhibit ory effect on pereoxydation of tissue lipids in the MDA test. The form ation of stable radicals for this type of compounds has been studied b y ESR. In addition, it has been found that 7-hydroxy-flavones are pote nt competitive inhibitors of xanthine oxidase. It is proposed that the C-7 OH of flavones may take the place of the C-2 or C-6 OH of xanthin e in the active site of the enzyme. A C-4' OH or C-4' OMe substitution on the 7-hydroxy flavones is not favourable to a fit in the active si te. The 2',3',4'-trihydroxy-flavones inhibited XO by another process, which remains to be determined. In summary, this study provides eviden ce that hydroxy-flavones exhibit interesting antioxidant properties ex pressed either by the capacity to scavenge free radicals (for 2',3',4' -trihydroxy-flavones) or to competitively inhibit xanthine oxidase (fo r 7-hydroxy-flavones). These compounds may be drug candidates for trea ting pathologies related to free radical oxidation.