Phytochemistry of Verbascum Species Growing in Iraqi Kurdistan and Bioactive Iridoids from the Flowers of Verbascum calvum

Abstract

Traditional medicine is still widely practiced in Iraqi Kurdistan, especially by people living in villages on mountainous regions; medicinal plants are also sold in the markets of the large towns, such as at Erbil, the capital of the Kurdistan Autonomous Region. About a dozen of Verbascum species (Scrophulariaceae) are commonly employed in the Kurdish traditional medicine, especially for treating burns and other skin diseases. However, the isolation of bioactive secondary metabolites from these plants has not been the subject of intense scientific investigations in Iraq. Therefore, the information reported in the literature about the species growing in Kurdistan has been summarized in the first part of this paper, although investigations have been performed on vegetable samples collected in neighbouring countries, such as Turkey and Iran. In the second part of the work, we have investigated, for the first time, the contents of a methanol and a hydromethanol extract of V. calvum flowers. The extracts exhibited weak antimicrobial activities, whereas the methanol extract showed significant antiproliferative effects against an A549 lung cancer cell line. Moreover, both extracts exhibited a significant dose-dependent free radical scavenging action against the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical, comparable to that of ascorbic acid. In the subsequent phytochemical study, a high phenolic content was determined in both extracts by the Folin–Ciocalteu assay and medium-pressure liquid chromatographic (MPLC) separation led to the isolation of iridoid glucosides ajugol and aucubin from the methanol extract. In conclusion, the high anti-inflammatory effects of aucubin and the remarkable antioxidant (antiradical) properties of the extracts give scientific support to the traditional use of V. calvum flowers for the preparation in Kurdistan of remedies to cure skin burns and inflammations.