Iridoid, phenylethanoid and flavonoid glycosides from Sideritis trojana

Abstract

The genus Sideritis is represented by 45 species in the flora of Turkey [1]. S. trojana Bornm., a perennial herb endemic to Kazdaglari (Ida Mountains), is utilized as an herbal tea for various purposes. Previously, several diterpenes were reported from S. trojana [2]. However, there is no report on its iridoid and phenolic constituents. In the continuation of our work on the bioactive secondary metabolites from Lamiaceae family, we now describe the isolation and structure elucidation of the secondary metabolites from the roots of S. trojana as well as their antioxidant activity. From the H2O-soluble portion of the MeOH extract, a new iridoid glycoside, 10-O-(E)-feruloylmelittoside (1) was obtained in addition to four known iridoid glycosides (melittoside,10-O-(E)-p-coumaroylmelittoside, stachysosides E and G). Moreover, five phenylethanoid glycosides (verbascoside, isoacteoside, lamalboside, leonoside A, isolavandulifolioside), three flavone glycosides (isoscutellarein 7-O-[6'''-O-acetyl-β-allopyranosyl-(1–2)]-β-glucopyranoside, 4'-O-methyisoscutellarein 7-O-[6'''-O-acetyl-β-allopyranosyl-(1–2)]-β-glucopyranoside, 3'-hydroxy-4'-O-methyisoscutellarein 7-O-[6'''-O-acetyl-β-allopyranosyl-(1–2)]-β-glucopyranoside) and a benzyl alcohol derivative (di-O-methylcrenatin) were obtained and identified. Characterization of the isolates was carried out by using NMR experiments and HR-MS. All compounds were tested for their antioxidant activity by in vitro TEAC assay and some of them exhibited moderate activity (0.97–1.44 mM) if compared with the reference compound (quercetin, 1.86 mM).