In vitro Antimicrobial Activity of a Semi-synthetic Derivative of Embelin

One of the strategies for the development of new drugs involves semi-synthesis of natural products. In the present study, the antimicrobial activity of embelin (1) and its semi-synthetic derivative 5-(p-tolylamino)-2-hydroxy-3-undecylcyclohexa-2,5-diene-1,4-dione (2) were evaluated against 21 bacterial and 4 fungal pathogens using the disc diffusion method. Embelin (1) was isolated from the fruits of Embelia schimperi Vatke by column chromatography over silica gel while its derivative (2) was synthesized in good yield (98.3%; w/w) by using a one-step condensation reaction after treating embelin with p-toluidine. The structures of these compounds were determined on the basis of 1H, 13C NMR, DEPT-135 and ESI-mass spectral data. Both 1 and 2 showed broad spectrum antibacterial activity against Gram-positive and Gram-negative bacteria at a concentration of 200 µg/ml. Among the tested bacteria, some strains of Escherichia coli, Salmonella typhi, Staphylococcus aureus and Vibreo cholera were found to be highly susceptible to the tested compounds with activity ranging between 75 and 94% of that of the standard drug ciprofloxacin. Similarly the tested compounds displayed good activity against four pathogenic fungal strains when with their effects were compared with that of griseofuvin.Keywords: Embelia schimperi, embelin, 5-(p-tolylamino)-2-hydroxy-3-undecylcyclohexa-2,5-diene-1,4-dione, antimicrobial, disk diffusion