Abstract
Two new rare sesquiterpene glycosides, macrochaetosides A (3) and B (4), together with two known metabolites: stigmasterol (1) and cyclostenol (2) were separated from the CHCl3 fraction of the aerial parts of Echinops macrochaetus Boiss. (Asteraceae). Their chemical structures were established based on various spectroscopic methods in addition to mass spectrometry and comparison with literature data. Moreover, the cytotoxic activity of these metabolites was assessed towards breast adenocarcinoma (MCF-7), human hepatocellular carcinoma (HepG2), and colorectal adenocarcinoma (HCT-116) tumour cell lines using sulphorhodamine B assay (SRB). Compounds 2 and 3 showed a potent cytotoxic profile towards all tested cell lines with IC(50)s 2.1, 2.9, and 3.6 mu M and 1.9, 3.3, and 2.3 mu M, respectively compared to doxorubicin (IC50 0.18, 0.60, and 0.20 mu M, respectively). Also, 4 exhibited cytotoxic activity against MCF-7 with IC50 6.9 mu M.