Antioxidant ability of chicoric acid and its analogous compounds

Active oxygen is known to play an important role in the development of aging, carcinogenesis and inflammation. Chapeu-de-couro, inhabiting in South America has been used as valid medical herb to rheumatism or hepatitis. Recently, it was reported that chicoric acid, which was extracted from Chapeu-de-couro, showed remarkable anti lipid peroxidation ability. In present study, it was undertaken to prepare chicoric acid and its analogous compounds. As a result, efficient preparative route to chicoric acid was established by using highly polar solvents, such as nitrobenzene, in esterification process. Then, correlation between chemical structure and antioxidant ability of these compounds was investigated by means of free radical scavenging ability test by the reaction with DPPH and anti lipid peroxidation ability test; these abilities were evaluated stoichiometrically per a unit mole of antioxidants by DPPH assay and thiobarbituric acid assay, respectively, and discussed in relation with their chemical structures, particularly focused on phenolic hydroxy, carboxylic and olefinic groups in these compounds. Catechol and hydroquinone derivatives consumed approximately two molar amounts of DPPH presumably to form corresponding quinones, followed by further oxidation. It was found that antioxidants having electron-withdrawing group remarkably enhanced both radical scavenging ability and anti lipid peroxidation ability.