Abstract: Objective To investigate the scavenging effects of on O2·and inhibiting effects on lipid peroxidation of the cinnamic - acid and its derivants. Method The methods of Nitro blue tetrazolium (NBT) and TBA were adopted respectively to determine half inhibiting concentration (IC50) on superoxide anioric free radical (O·) and the contents of Malonic dialdehyde (MDA) of - 2 liver microsome lipid peroxide (LPO) products of the cinnamic acid and its derivants. Result The O·scavenging effects of caffeic - 2 acid, chlorogenic acid, forsythiaside and ferulic acid were strong while, p-coumaric acid, o-coumaric acid and m-coumaric acid had relatively weak O·scavenging activity, but cinnamic acid had no O·scavenging activity. The derivants of cinnamic acid can - - 2 2 effectively inhibit the iron-induced lipid peroxidation of rabbit liver microsomes in a concentration-dependent manner, but cinnamic acid can not. Conclusion The seven kinds of derivants of cinnamic acid all had distinctive effects on anti-oxidation, but cinnamic acid had not. The relationship of structure and the O· scavenging activity revealed that the phenolic hydroxyl structural - 2 group in benzene ring was the important determinant for O· scavenging but not -CHCHCOOH structural group. The reactivity - 2 of phenolic hydroxyl could increased if there is a heteroatom with p-tape lone pair of electrons (such as -OH,-OCH3) in its ortho position of it, while phenolic hydroxyl in the para position of –CHCHCOOH had relatively strong reactivity.

Key words: anti-oxidation, superoxide anionic free radical (O·), lipid peroxidation(LPO), the relationship of - 2 structure and activity