Isolation and Chemical Structural Characterization of the Mixture of Two Related Phytosterols from Ricinus communis L. (Euphorbiaceae) Leaves

Abstract

Aim: Ricinus communis, a member of the family Euphorbiaceace, is widely used in South African traditional medicine for the treatment of wounds, sores and boils. The plant was selected based on a high antibacterial activity demonstrated in a previous In vitro study. There is a need to isolate compounds that are responsible for antibacterial activity of R. communis leaves. Methodology: The leaves of R. communis were milled to a fine powder and sequentially extracted with n-hexane, dichloromethane, acetone, and methanol using a serial exhaustive extraction method. Thin layer chromatography was used to analyse the phytochemical components of the extracts and bioautography for the presence of antibacterial compounds. A pure compound was isolated using column chromatography coupled with preparative thin layer chromatography and the structure was elucidated by nuclear magnetic resonance. Results: Hexane extracts had potent antibacterial activity against Escherichia coli and Original Research Article Masoko and Nemudzivhadi; EJMP, 10(2): 1-11, 2015; Article no.EJMP.18172 2 Enterococcus faecalis and low activity against Pseudomonas aeruginosa and Staphylococcus aureus. The average minimum inhibitory concentration value of hexane crude extracts was 0.47 mg/ml, followed by extracts of dichloromethane (0.94 mg/ml), acetone (0.39 mg/ml) and methanol (1.49 mg/ml). The bioassay guided fractionation of the hexane extract led to the successful isolation of compound 1 at the Rf value of 0.40. Compound 1 was identified as a mixture of stigmasterol and β-sitosterol. Conclusion: Compound 1 lost its antibacterial activity during the purification process. This may lend support to the theory that some compounds present in plant extracts act synergistically to give a particular biological activity. This study represents the first report of the isolation of stigmasterol and β-sitosterol from the leaves of R. communis.