Synthesis and evaluation of new phenolic-based antioxidants: Structure–activity relationship

The structure–activity relationships of synthetic phenolic-based derivatives as potential antioxidants have been investigated. Their efficiency as radical scavengers was evaluated by their activity towards the stable free radical, 2,2-diphenyl-1-picrylhydrazyl (DPPH ) and their potency as antioxidants in food was evaluated in refined olive oil using the Rancimat method. Four of the new antioxidants possessed better radical-scavenging capacity than the natural antioxidant hydroxytyrosol ( 2). They were galloyl alcohol ( 12), containing three phenolic hydroxyl groups and a primary alcohol, and the ortho-diphenolic derivatives dihydrocaffeoyl alcohol ( 3), caffeoyl alcohol ( 4) and 5-methoxy-protocatechuyl alcohol ( 13). Two of these antioxidants, 3 and 12, also showed higher antioxidant capacity than 2 in stabilising olive oil. The contribution of the length of the alkyl chain linking the phenyl ring to the primary alcohol, with regard to its antioxidising potency was studied and contradictory results were obtained. The polar paradox fails to explain the antioxidant capacity found for these new phenolic antioxidants, except from a very general perspective.