Phytochemical and biological investigations on Verbascum bugulifolium L.

The genus Verbascum comprises about 255 species in the Flora of Turkey. The flowers and leaves of some Verbascum species are used for the treatment of rheumatic disorders, eczema, spasmodic coughs, as an antiseptic and expectorant agent in different traditional systems. In this study, the antioxidant (DPPH•, ABTS• and CUPRAC), anti-inflammatory (LOX inhibition) and antimicrobial activities of the crude MeOH extract and its subextracts obtained from the aerial parts of Verbascum bugulifolium were investigated by in vitro methods. Among the tested extracts, EtOAc and n-BuOH subextracts exhibited the highest antioxidant activity in DPPH, ABTS and CUPRAC assays (IC50 = 20-90 µg/mL). The in vitro anti-inflammatory activity of the extracts was measured using a LOX inhibition assay where n-BuOH subextract provided a 35.7% inhibition at 50 µg/mL. The antimicrobial activity of the extracts was also evaluated against three bacteria and three fungal strains. Only the n-hexane subextract indicated remarkable antibacterial activity against P. aeruginosa ATCC 10145 (MIC = 125 µg/mL), while CHCl3 subextract showed moderate activity against C. krusei ATCC 6258 (MIC= 250 µg/mL). Subsequent chromatographic studies on the n-BuOH, EtOAc and CHCI3 subextracts yielded five iridoid glycosides [catalpol (1), specioside (2), ajugol (3), ajugoside (4), 8-O-acetylharpagide (5)]; two phenylethanoid glycosides [verbascoside (6), and glucopyranosyl-(1Gi-6)-martynoside (7)]; five flavonoids [luteolin (8), luteolin 7-O-β-D-glucopyranoside (9), luteolin 7-O-rutinoside (10), apigenin 7-O-rutinoside (11), quercetin 3-O-rutinoside (12)]; and one phytosterol [β-sitosterol (13)]. Compounds 2 and 6-8 elicited the equipotent or quite higher ABTS scavenging activity compared to the standard ascorbic acid in the range of 10-30 g/mL. Compound 6 showed the highest CUPRAC activity, which was as good as gallic acid with IC50=10 g/mL. Compounds 6 and 8 showed the highest antioxidant activity in all tests where 8 showed a relatively remarkable anti-inflammatory activity compared to other samples with 54.1 % inhibition at 1 µg/mL. All the tested compounds indicated weak antimicrobial activity against tested microorganisms. This is the first phytochemical and bioactivity study on V. bugulifolium. Key Words: Verbascum bugulifolium; Scrophulariaceae, secondary metabolites, iridoid glycosides; phenolic compounds; antimicrobial, antioxidant and anti-inflammatory activities