Antibacterial effects of cyanogenic glucoside isolated from the stem bark of Bauhinia rufescens Lam
The chemical contents and in vitro antibacterial effects of the n-butanol column fractions, stem bark methanol extracts of Bauhinia rufescens Lam. were evaluated in Gram-positive and Gram-negative bacteria using disc diffusion technique. The n-butanol soluble portion from the stem bark methanol extract was successively eluted to afford 10 pooled fractions by comparison of TLC chromatograms. The bioactive fraction (fraction D) was further chromatographed using the bioassay guided protocol to afford 4 sub-fractions from which a pure compound was isolated and characterized using spectral studies as: (4S, 6R)-(Z)-6-(â-Dglucopyranosyloxy)-4-hydroxy-2-cyclohexenyl-Ä1,á-acetonitrile–a cyclohexenyl cyano methylene known commonly as menisdaurin. Test bacteria were Bacillus subtilis, Corynaebacterium spp., Escherichia coli and Shigella dysenteriae. The diameters of inhibition zone on the Gram-positive bacteria was found in the range from11.83±0.17 (n-butanol Fraction D) to 17.33±0.67 (Fraction D2-8); while on Gram-negative organism the values ranged from 11.50±0.29 (n-butanol Fraction D) to 19.67±0.33 (Fraction D2-8). The activity index (AI) showed that Fraction D2-8 (51.18%) and Compound I [menisdaurin] (127.36%) was highly sensitive to Corynaebacterium spp. and E. coli when computed with Erythromycin and Gentamicin respectively. Highest AI was exhibited by Fraction D2-8 (93.89%) against S. dysenteriae when computed with ciprofloxacin. In continuation of our chemical studies and search for bioactive compounds from medicinal plants; this work, therefore, was aimed at characterizing and testing the antibacterial efficacy of the isolated compound in order to further confirm our earlier reports on use of this part of B. rufescens in some parts of Northern Nigeria as a
treatment against diarrhoea and dysentery. This is the first report of the isolation and antibacterial activity of menisdaurin from B. rufescens.
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Keywords: Antibacterial, Bauhinia rufescens, cyanogenic glucoside, isolation, menisdaurin.
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