Antioxidant iridoid and phenylethanoid glycosides from Teucrium chamaedrys (L.)

Wall Germander (Teucrium chamaedrys) is a Mediterranean species used as medicinal herb. A previous screening turned to the radical scavenging efficacy determination was carried out on crude extracts from T. chamaedrys ipogeal and epigeal components undergoing each one to DPPH radical antioxidative HAT assay. Leaf and root methanolic extracts are responsive of a peculiar DPPH radical scavenging efficacy. The methanolic crude extracts were object of extractive and chromatographic analyses to yield twelve compounds: seven iridoid and five phenylethanoid glycosides, four of them isolated and characterized for the first time on the basis of their spectroscopic features. The DPPH radical scavenging and antioxidant capabilities of the purified metabolites were assessed. The antioxidant capability in cell-free systems of the isolated metabolites was carried out by measuring their capabilities to inhibit the synthesis of thiobarbituric acid reactive in assay media using as oxydable substrates a vegetable fat and the pentose sugar 2-deoxyribose. The inhibiting capacity of isolated metabolites the protein oxidation, defined as the covalent modification of a protein induced either directly by reactive oxygen species or indirectly by reaction with secondary by-products of oxidative stress, was also measured. Compounds from T. chamaedrys were tested in increasing concentration (5.0µM, 10.0µM and 20.0µM) in triplicate analysis. The detected activities were compared to those exercised from Trolox®. When DPPH radical scavenging was tested, phenylethanoid glycosides highly reduced the oxidant probe employing an activity strongly dose-dependent. Iridoid glycosides prevent massively the 2-deoxyribose and BSA oxidations in assay media. The results show that oxidation and radical processes are highly complex and involve various mechanisms and targets. In particular the ability to scavenge free radical does not necessarily confer antioxidant properties.