Phytochemical Analysis, Biological Activity And Molecular Docking Studies Of Root Extracts Of Lobelia Rhynchopetalum Hemsl.

Abstract

Lobelia rhynchopetalum, commonly known as Jibara (Amharic),Terura (Afan Oromo), which is endemic to Ethiopia, has been traditionally used by the Arsi people for the treatment of various diseases such as leprosy, wound, evil eye, retained placenta, diarrhea, fever, eye disease, rabies and tumor/cancer. In view of its traditional uses and the absence of scientific reports so far, an attempt was made to explore the chemical, antibacterial and antioxidant potential of the solvent extracts of the roots of L. rhynchopetalum. In this regard, the roots (350 g) were successively extracted with n-hexane separately, the solution was filtered, and the defatted residue was extracted with dichloromethane/methanol (1:1) and methanol to give 13.40 g and 7.3 g (3.83 % and 2.08% ) yields, respectively. Phytochemical screening analysis conducted on roots extracts of L. rhynchopetalum showed the presence of alkaloids, anthraquinone, tannins, terpenoids, anthraquinoneglycosides, cardiac glycosides and anthranol glycosides. Silica gel column chromatographic separation of the crude extract of dichloromethane: methanol (1:1) afforded a polyacetylenic alcohol, lobetyol (1), a triterpenoid, 24-ethyl-3-hydroxylcholesta-5,25-diene (2), a pyrolidine alkaloid, lobechine (3), a fatty acid lauric acid (4), anthraquinones, chrysophanol (5) and physcion (6). Since the plant has never been investigated for its phytochemical constituents, this is the first report of isolation of these compounds from the Arsi-Bale Mountains plant. Moreover, chrysophanol and physcion are identified from the species for the first time. The structures of compounds were characterized using spectroscopic methods ( 1H NMR, 13C NMR, and DEPT-135). The extracts and isolated compounds were also evaluated in vitro for their antibacterial activities using disc diffusion method against E. coli, S. aureus, and S. pyogenes. Strong inhibition zone values ((15±1,14.33±0.58, 15.67±0.58 mm for lobetyol (1) were observed against E.coli, S.aureus and S.pyogenes respectively, when compared to standard ciprofloxacin (19±1, 17.33±1.53 and 19.67±0.58 mm). The DPPH radical scavenging activities (%) of extracts and isolated compounds were found to be 71.6 (compound 1), 27.2 (compound 2), 70 (DCM: MeOH (1:1) extract), 60.9 (Acid- base extract) and 67.2 (compound 3) respectively at 100 µg/ml, Suggesting that compound 1 and 3 displayed slightly highest radical scavenging activity indicating the potential of the plant as herbal remedies.