Antioxidant properties of 4-vinyl derivatives of hydroxycinnamic acids.

The compounds 4-vinylphenol (4-VP), 4-vinylguaiacol (4-VG), 4-vinylsyringol (4-VS) and 4-vinylcatechol (4-VC) were prepared by thermal decarboxylation of the corresponding hydroxycinnamic acids p-coumaric, ferulic, sinapic and caffeic acid, respectively. For confirmation of the synthesised products LC-MS followed by NMR analysis was used. To evaluate their antioxidant potential, their reducing power and efficiency in scavenging the alkylperoxyl radical generated in an emulsion system, the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical and the superoxide anion radical (O2(-)) were determined. All tested 4-vinyl derivatives revealed weaker antioxidant activity in a homogeneous polar medium than the corresponding phenolic acids. In the emulsion system the activity for 4-vinyl derivatives was higher than was the activity of their corresponding phenolic acids, with 4-VG as the most active among the tested phenolic compounds.