Bioactivities of Verbascum bugulifolium and isolation of secondary metabolites

The genus Verbascum (mullein) comprises about 250 species in the flora of Turkey. Some species are used for the treatment of rheumatic disorders, eczema, spasmodic coughs, as an antiseptic and expectorant agent in different traditional systems [1]. In the continuation of our phytochemical and bioactivity studies on Turkish medicinal plants, we have investigated the antioxidant, anti-inflammatory and antimicrobial activities of the crude MeOH extract from the aerial parts of Verbascum bugulifolium as well as the subextracts obtained thereof, for the first time. Among the tested extracts, EtOAc and n-BuOH subextracts exerted the best antioxidant activity in DPPH, ABTS and CUPRAC assays (IC₅₀ = 0.02 – 0.09 mg/mL). The in vitro anti-inflammatory activities of the extracts were evaluated using a LOX inhibition assay where n-BuOH subextract caused a 35.7% inhibition at 50 µg/mL. The antimicrobial activities of the extracts were also tested against three bacteria and three fungal strains. Only the n-hexane subextract showed antibacterial activity against Pseudomonas aeruginosa ATCC 10145 (MIC = 0.125 µg/mL), while CHCl₃ subextract exerted moderate activity against Candida krusei ATCC 6258 with a MIC value of 0.25 mg/mL, which is followed by n-BuOH and and n-hexane subextracts with a MIC of 0.5 mg/mL. Due to activity of the n-BuOH and EtOAc subextracts, chromatographic purifications were conducted, where five iridoid glycosides catalpol, specioside, ajugol, ajugoside, 8-O-acetylharpagide, two phenylethanoid glycosides, verbascoside and glucopyranosyl-(1-G_i-6)-martynoside, three flavonoids, apigenin 7-O-rutinoside, luteolin 7-O-β-D-glucopyranoside, luteolin 7-O-rutinoside were purified from the n-BuOH extract, while luteolin were obtained from the EtOAc subextract.

[1] Alipieva KI, Erdoğan Orhan I, Tatli Cankaya I, Emanuela P, Kostadinova, EP, Georgiev MI. Phytochem Rev 2014; 13: 417 – 444.