ON THE ANTIOXIDANT PROPERTIES OF THREE SYNTHETIC FLAVONOLS

MONTAÑA M.P.; PAPPANO N.B.; GIORDANO S.O.; MOLINA P.; DEBATTISTA N.B.; GARCÍA N.A.

PHARMAZIE

Govi-Verlag

Lugar: Alemania; Año: 2007 vol. 62 p. 72 - 76

0031-7144

The antioxidant properties of a series of synthetic and natural flavonoids towards the oxygenated species superoxide radical anion (O2.-) enzimatically generated, were evaluated. 7-hydroxyflavonol, 7,3´-dihydroxyflavonol and 3´-hydroxyflavonol were synthetized, with a systematic variation of the   OH substitution on positions C3, C7, C3´and C4´, and their respective antioxidative abilities compared to those of the already characterised  natural flavonoids Quercetin, Kaempferol and Rutin. The efficiency of O2.- deactivation by the flavonoids does not correlate with  their respective determined oxidation potentials, suggesting that the pure one-electron-transfer-mechanism of O2.- quenching could not be the main scavenging process involved. Experimental evidence demonstrated that the possible inhibition of the O2.--generator enzymatic system by the flavonoids must be disregarded as a possible indirect cause for the inhibition of the oxidative species. One possible mechanism for the inhibition of O2.-, highly dependent on the substitution pattern of the flavonoid,  may be the generation of hydroperoxides or dioxetanes as oxidation products, as already postulated for other biologically relevant compounds. The simultaneous OH-substitution on positions C3 and C7 of the flavonoid skeleton plays a definitive role in the enhancement of the O2.- inhibitory effect. The replacement of OH by a O-rutinosyl group on position C7 suppresses at all that effect, whereas the absence of an OH group in position 7 significantly reduces the antioxidative power. Finally, the presence of OH groups on positions 3´ and 4´ do not produce any determinant consequence in the antioxidative behaviour of the flavonoids.