Antibacterial saponins from the leaves of Polyscias fulva (Araliaceae)

Abstract

Saponins are a major family of secondary metabolites that occur in a wide range of plant species. Bioassay - guided fractionation of extract of the leaves of Polyscias fulva led to the isolation of three known saponins named, 3-O-α-L-arabinopyranosyl-hederagenin (1), 3-O-[α-L-rhamnopyranosyl(1-2)-α-L- arabinopyranosyl]-hederagenin (2) and 3-O-[rhamnopyranosyl-(1→2)-xylopyranosyl]-Olean-12-en-28-O- [rhamnopyranosyl-(1→4)-glucopyranosyl-(1→6-glucopyranosyl] ester) (3). Leaves of the plant were collected from Kakamega rain forest in Kenya, dried under shade and ground into fine powder and extraction was done using methanol. The methanol extract was subjected to column chromatography and the fractions purified using preparative high performance liquid chromatography (HPLC). The bioactivity of the pure compounds was done using disc diffusion method. The three compounds exhibited moderate activities against Gram positive bacterium (Staphylococcus aureus ATCC25922) and Gram negative bacterium (Klebsiella pneumoniae ATCC13883). Compound 1 was found to be the most active against K. pneumoniae (8.00±1.00 mm) and S. aureus (10.00±1.73 mm) followed by compound 2 with inhibition zones of 7.66±0.57 and 7.33±0.57 mm against K. pneumoniae and S. aureus, respectively. Compound 3 was the least active against both K. pneumoniae (7.33±0.57 mm) and S. aureus (7.00±1.00 mm). The results obtained indicate that compounds 1, 2 and 3 exhibit potential as possible sources of antibacterial agents.