Molecular docking, antimicrobial, antibiofilm formation, and antiproliferative activities of furano-based sesquiterpenoids from Euryops arabicus

Background
Euryops arabicus is well known in the Arabian Peninsula as traditional herbal medicine. The plant synthesizes various types of flavonoids, terpenes, and furoermophilanes skeletons in either steroidal or nonsteroidal conformation, and this wide range of chemical compounds might play an increasingly prominent role in medicine. This study aimed to isolate pure secondary metabolites and assess their antibacterial, antiproliferation, and antibiofilm formation properties.

Methods
The organic extract of the areal parts of E. arabicus was chromatographically fractionated to afford pure compounds characterized using NMR, UV, and IR along with mass spectrometry. The activity of the isolated compounds was assessed against three cancer cells and a set of Gram-negative and positive bacteria.

Results
Four specific sesquiterpenoids were identified: 6β-senecioyloxy-1,10-dehydrofuranoeremophilan-9-one (1), 6β-acetoxy-9-oxoeuryopsin (2), 6β-(2′-methyl, 2′,3′-epoxy-butyryloxy)-euryopsin (3), and 6β-angloyloxy-1,10-dehydrofuraoeremophilan-9-one (4). Molecular docking studies indicated the epidermal growth factor receptor and methionyl-tRNA synthetase as probable antibacterial and antiproliferative activities of the compounds. In the in vitro studies, compounds 2 and 4 showed remarkable activity against all examined Gram-negative and positive pathogens with inhibition diameters (mm) ranging from 13.1 ± 0.23 to 19.0 ± 0.44 and 12.9 ± 0.20 to 16.2 ± 0.23, respectively. Compounds 2 and 4 showed moderate biofilm formation inhibition of both Pseudomonas aeruginosa and Staphylococcus aureus with 58% and 79%, respectively. Moreover, the isolated sesquiterpenoids showed potent antiproliferative activities against MCF-7, HepG2, and HCT116 human cancer cells.

Conclusion
Four sesquiterpenoids were isolated from E. arabicus. Compound 2 showed a relatively high antibacterial and cytotoxic activity. Additional studies are recommended to substantiate the observed activities further.