Studies on structure–activity relationships are vital forunderstanding the molecularmechanisms of biochemical processes. Such concepts have also been applied to the development of effective biological antioxidants, the importance of which is emerging from increasing evidence on the role of oxygen-derived free radicals in many degenerative diseases.
Berberine and berberine-type alkaloids representing a structural class of organic cations, produced in numerous plants of the genera Berberis, Mahonia, and Coptis, have been shown to exert a broad spectrum of antimicrobial, anticancerogenic, and antimutagenic activity.
Coptisine, berberine, and jatrorrhizine, the main protoberberine alkaloids from Coptis japonica, showed strong antiphotooxidative activity in the chlorophyl-sensitized photooxidation of linoleic acid, which was shown to be due to singlet oxygen quenching. These compounds were also shown to exert weak antiperoxidative activity in rat liver microsomes. Antiperoxidative features of other protoberberine and aporphine alkaloids have been also reported.
Focusing on the mechanism of action of these alkaloids, we hypothesize that the presence of aromatic –OH group may be responsible for their antioxidant efficiency, similarly to phenolic antioxidants via chain-breaking mechanism by donation of phenolic hydrogen.