Phytochemical and in Vitro Anti-Microbial Screening of Echinops Hispidus Fresen. and Grewia Similis K. Schum.
Muithya, James N.
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Antimicrobial resistance is reported to be on the increase due to gene mutations of the disease causing pathogens. It is believed that, new antibiotics with activities and structures different from those in current use could be found through ethnobotanical route. This requires a follow up of promising leads with attempts to isolate and identify the active principles from the medicinal plants. Two Kenyan plants Echinops hispidus Fresen. (Asteraceae) and Grewia similis K. Schum. (Tiliaceae) were selected for this study because of their reputation in folklore medicine as antimicrobial agents. The antimicrobial screening of the crude extracts and the isolated compounds was done using the agar diffusion method. The ethyl acetate (EtOAc) root extract of E. hispidus showed a weak activity with an inhibition zone of 9 mm against Staphyloccocus aureus. The hexane/dichloromethane (DCM) root extract of G. similis exhibited a very strong activity with an inhibition zone of 15 mm. the hexane, DCM and EtOAc root extracts of E. hispidus showed a weak activity of 9mm, strong activities of 13 and 15 mm against Cryptoccocus neoformans, respectively. The hexane and DCM extracts of E. hispidus and the hexane/DCM extract of G. similis showed the minimum activity of 6 mm against Pseudomonas aeroginosa and Escherichia coli. Isolation and separation of the crude extracts were carried out using VLC, CC, TLC and centrifugation. This led to isolation of eight compounds whose structures were determined by Infrared, Ultraviolet, 1D- and 2D-NMR, MS and correlation with published data. The hexane/DCM extract of the whole root of G. similis led to isolation of 3β-sitosterol (112) and 3β-stigmasterol (113). These compounds are being reported for the first time from this plant. The root hexane extract of E. hispidus led to isolation of six compounds; 3β-acetyl taraxerol (114), cameroonan-7α-ol (115), membrin-8α-ol (116) and membrinol-8β-0l (117), 4-[5-(penta-1,3-dieynyl) thien-2-yl] but-3-ynyl (119). The dichloromethane extract of the whole root of E. hispidus yielded 4-[5-(penta-1,3-dieynyl) thien-2-yl] but-3-ynyl diol (120). Compounds 115, 119, 114, 116, 117, 119 and 120 are being reported fore the first time from E. hispidus. The ethyl acetate root extract of E. hispidus and the hexane/DCM root extract of G. similis showed antibacterial activities against Staphylococcus aureus with inhibition zones of 9, 13 and 15 mm, respectively. The isolated compounds 112 , 113 and 120 showed mild antibacterial activities of 8 mm against S. aureus. Compound 119 showed a moderate antibacterial activity of 10 mm against S. aureus. The compounds 119 and 120 showed high antifungal activities of 33 and 27 mm against C. neoformans, respectively. The biologically active compounds are templates for synthesis of more potent and water soluble derivatives. These antimicrobial activities support the use of E. hispidus and G. similis for the treatment of antimicrobial related ailments by the Kipsigis and Maasai communities