Date Published: April 30, 2018
Author(s): Babe Guyasa, Yadessa Melaku, Milkyas Endale.
Embelia schemperi Vatke is one of the medicinal plants used traditionally for treatment of intestinal tape worm, dysmenorrheal, bacterial, and fungal infections. Phytochemical screening test of the dichloromethane/methanol (1 : 1) and methanol extracts revealed the presence of phenols, alkaloids, tannins, and flavonoids whereas terpenoids, glycoside, and phytosterols were absent. Silica gel column chromatographic separation of the methanol extract afforded 3,5,7,3′,4′-pentahydroxyflavan, named epicatechin (1), along with a close flavan derivative (2). Structures of the compounds were elucidated by spectroscopic techniques (1D and 2D NMR, FTIR, and UV-Vis). The crude extracts and isolated compounds were screened for in vitro antibacterial activity against strains of Klebsiella pneumoniae, Escherichia coli, Cryptococcus neoformans, Shigella dysentriae, and Staphylococcus aureus. Epicatechin (1) exhibited comparable antibacterial activity against S. aureus and E. coli (15 and 12 mm zone of inhibition, resp.) to that of the control antibiotic gentamicin, with zone of inhibition of 15 and 12 mm, respectively, at a concentration of 20 µg/mL.
Medicinal plants have been a major source of cure for human diseases since time of immemorial. As modern techniques, for example, genomics, high-throughput screening, and target-oriented drug development strategies, have not yet fulfilled the expectations that appeared promising upon their introduction, chemotherapeutics remain the cornerstone of patient management and will likely remain so for the foreseeable future. Rapid resistance development of microorganisms to existing medicines reveals the essential need for drugs with novel modes of action. Though a number of antibacterials have been reported from natural source or their derivatives, evaluation of plant-based indigenous medicines still appears as one of the promising sources of novel antibacterial leads.
This work resulted in the isolation of two flavan compounds (1, 2) isolated for the first time from the stem bark of Embelia schimperi. The structures of the compounds were characterized on the basis of spectral data (UV-Vis, 1H-NMR, 13C-NMR, DEPT-135, HMBC, HSQC, COSY, and IR) as well as in comparison with the literature report. The antibacterial test results revealed that the isolated compounds showed promising antibacterial activity against Staphylococcus aureus, E. coli, Proteus mirabilis, and Klebsiella pneumoniae. Epicatechin (1) exhibited comparable (15 mm zone of inhibition) antibacterial activity against S. aureus to that of gentamicin (15 mm zone of inhibition). Compound 2 also exhibited promising antibacterial activity against S. aureus and E. coli and 11 and 13 mm zone of inhibition, respectively, compared to that of gentamicin (15 mm zone of inhibition).