Phytochemical Investigation And Antimicrobial Activity Of Blighia Unijugata Bak (Sapindaceae)
Blighia unijugata Bak (Sapindaceae) is a plant used in traditional medicine for the treatment of various ailments. An infusion of the pounded roots is used to treat fever in East Africa. The roots, pods and leaves of the plant have been used for their hemostatic, anthelminthic and tonic properties. Infections are a major cause of fever and the use of the plant in the treatment of fever may be attributed to phytochemicals with antimicrobial properties. The objectives of this study were to carry out an investigation of the phytochemical constituents as well as to screen for the antibacterial and antifungal activities of the bark of B. unijugata. The plant material was collected from Kiangwachi in Kirinyaga Disrict in November 2007, identified, air-dried, milled and stored in plastic containers. Preliminary phytochemical screening revealed the presence of saponins, tannins and glycosides in the plant. Using a Soxhlet extractor, the milled bark was extracted sequentially with petroleum ether (60-80 °C), chloroform and methanol, each extraction Iastingd S h. Soxhlet extraction was the preferred method of extraction because it is efficient and exhaustive. The chloroform extract was reduced under vacuum and fractionated with the aid of isocratic open column chromatography. Normal-phase silica gel for column chromatography and chloroform were the stationary and mobile phases, respectively. Systematic purification of the fractions thus obtained afforded three compounds which crystallized from a chloroform/ethyl acetate mixture. The purity of these compounds was monitored using thin layer chromatography. With the aid of mass, infrared, nuclear magnetic resonance and ultraviolet/visible spectroscopic data, two of the compounds were identified as the pentacyclic triterpenoids friedelin and epifriedelinol. The structure of the third compound could not be fully elucidated as it was not possible to tell the molecular ion from its crowded mass spectrum. In vitro antibacterial and antifungal activity of the petroleum ether, chloroform and methanol bark extracts and friedelin was tested using the agar diffusion method. The concentrations used were 50 mg/ml for the extracts and 50 ug/rnl for the pure compound. The bacterial strains used in this study were Pseudomonas aeruginosa, Staphylococcus aureus and Escherichia coli, while the fungi employed included Cryptococcus neoformans, Candida albicans, Trichophyton mentagrophytes and Microsporum gypseum. The methanol and chloroform extracts together with the pure compound, friedelin, were active against S. aureus with zones of inhibition of 18.0, 22.0 and 10.0 mm, respectively. Gentamicin at a concentration of 10 ug/rnl was used as the positive antibacterial control and gave a zone of inhibition of 26.0 mm against S. aureus. In the antifungal activity screening, the methanol extract was found to be active against C. albicans and M gypseum giving zones of inhibition of 10.0 and 13.0 mm, respectively. The positive antifungal control was fluconazole at a concentration of 25 ug/ml with zones of inhibition of 19.0 and 20.0 mm, respectively, against the two fungal species. The present study may support the use of this plant in folklore for the treatment of infections where fever is usually present. However, the isolated compounds may not be responsible for the antipyretic activity of the plant. This is due to the fact that the compounds were isolated from a non-polar solvent while only the polar formulations, usually water decoctions and infusions, are used in traditional medicine. Furthermore, the pure compound screened in this study had very low activity. Therefore, the polar extracts - including alcoholic and water extracts - of the plant need to be studied with the aim of isolating more bioactive compounds. Additionally, the plant should be subjected to a wider array of bioassays including antipyretic and antiplasmodial activity testing.