Background: Many plants growing in Saudi Arabia are used in folk medicine for treatment of several diseases. Objective: Information of the chemical constituents and biological activities of plants is desirable for the discovery of therapeutic agents and discovering the actual value of folkloric remedies. Materials and Methods: The compounds were isolated and purified using silica gel column chromatography and preparative high-performance liquid chromatography-diode array detector (HPLC-DAD) Method. The alcoholic extracts of these plants were evaluated for biological activities. Results: Isolation and characterization of 1-feruloyl-?-D-glucopyranoside (1) as well as new secondary metabolite tryptophan methyl ester (2) were isolated for the 1st time from the Horwoodia dicksoniae. The three flavones were isolated from Rumex cyprius identified as isoorientin (3), vitexin (4), and Cynarosid (5). The structures of these compounds were characterized by nuclear magnetic resonance and mass spectrometry analysis and comparing with literature. The compounds were isolated and purified using silica gel column chromatography and preparative HPLC-DAD Method. The alcoholic extracts of these plants were evaluated for antimicrobial activities against two Gram-positive bacteria, two Gram-negative bacteria, and four pathogenic fungi. Both plants showed good activities against Syncephalastrum racemosum and Streptococcus pneumoniae with minimal inhibitory concentrations (MICs) 0.98 and 1.95 μg/mL, respectively. H. dicksoniae showed good activity against Aspergillus fumigates with an MIC 1.95 μg/mL. The two extracts showed also effective free radical scavenging activities in the 1,1-diphenyl-2-picrylhydrazyl assay. H. dicksoniae exhibited remarkable cytotoxic activity against Human breast cancer mammary cancer cells-7, Human liver cancer human hepatoma carcinoma cells-2, and human lung carcinoma (A-549) cell lines. Conclusions: It was suggested that further work should be carried out to isolate, purify, and characterize the active constituents responsible for the activity of these plants.
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