Secondary metabolites from two endemic Stachys cretica subspecies and their antioxidant properties

Abstract

The genus Stachys is one of the largest genera of the Lamiaceae family including about 300 species growing wild in the tropical regions of both hemispheres and represented by more than 80 species in the Flora of Turkey. We aimed to elucidate the structure of major phenylethanoid glycosides and flavonoids present in two endemic subspecies namely Stachys cretica ssp. lesbiaca and S. cretica ssp. trapezuntica and evaluate their antioxidant activities through several biochemical assays including inhibition of lipid peroxidation in soybean phosphatidylcholine liposomes induced with Fe3+/ascorbate, scavenging effect on DPPH· and superoxide radicals, reducing power and ABTS radical cation decolorization. Succesive coloumn chromatography of the ethyl acetate subfraction of two subspecies led to isolation of acteoside, leucosceptoside A, martynoside as major phenylethanoid glycosides and isoscutellarein-7–0-[6'''-acetyl-allosyl(1→2)]glucopyranoside, 3'-hydroxy-4'-0-methylisoscu- tellarein-7–0-[6'''-acetylallosyl(1→2)]glucopyranoside and 4'-0-methylisoscutellarein-7–0-[6'''-acetyl-allosyl(1→2)]glucopyranoside as flavonoids. The antioxidant activities of the compounds were compared to that of quercetin as a typical example of a naturally occurring flavonol. All isolated metabolites showed moderate antioxidant activity. Among the tested compounds acteoside was found to be the most active.