Antimicrobial and Antioxidant Potentials, and Chemical Constituents of the Leaf Extracts of the Nigerian Piliostigma thonningii (Caesalpiniaceae) Schum

Aims: In this work the 95% ethanol extract of the Nigerian Piliostigma thonningii known traditionally to possess a number of medicinal properties was screened for antimicrobial and antioxidant potentials as well as identified its chemical constituents. It was to confirm its traditional medicinal uses.

Study Design: The various local sources of the plant were identified for the collection of the leaves. The plant was authenticated by a taxonomist and a voucher specimen kept for future reference. The plant sample was extracted using 95% ethanol and the crude extract screened for phytochemicals and fractionated. The crude extract and fractions were screened for antimicrobial and antioxidant potentials. The antimicrobial hexane fraction was subjected to chromatographic separation to isolate the chemical constituents. Also, the fresh leaves were hydrodistilled to obtain the volatile components. The column isolates and volatile components were identified using GC-MS analysis.

Place and Duration of Study: The study was undertaken between October 2011 and April, 2013, in the Department of Chemistry, University of Abuja, Nigeria and the Advanced Chemistry Laboratory, Sheda Science and Technology Complex, Sheda, Abuja, Nigeria.

Methodology: The air-dried leaves powder of P. thonningii was extracted with 95% ethanol to obtain the crude extract. The fresh leaves were also hydrodistilled to obtain the volatile oils. The crude extract was fractionated into acidic, basic, non-polar neutral and polar neutral fractions. It was screened for phytochemicals using standard procedures. Both the crude extract and fractions were screened against some pathogens, including Escherichia coli, Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, Streptococuss spp. and Salmonella spp. The antioxidant potential of the crude extract was also determined using standard procedures. The antimicrobial hexane fraction was subjected to Flash column chromatography. The isolates and the volatile oil were analyzed for their constituents using GC-MS.

Results: The crude extract showed the presence of sterols, phenolics, alkaloids, flavonoids, glycosides, triterpenes, and tannins, but no carbohydrates. The crude extract and fractions and the hydrodistillate showed potential activity against the test organisms including, Escherichia coli, Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, Streptococuss spp. and Salmonella spp. The crude extract equally showed antioxidant potential in DPPH. Column chromatography of the hexane fraction followed by GC-MS analysis led to the identification of lupeol and lup-20(29)-en-3-one. GC-MS analysis of the volatile oil from hydrodistillation of the fresh leaf revealed the presence of 2,5-octadecadiynoic acid, cholestan-3-ol, 2-methylene, isoaromendrene, trans-Z-α-bisabolene epoxide,1-methyl-6-(3-

methybuta-3-dienyl)-7-oxabicylo [4.1.0] heptane and aromadendrene oxide.

Conclusion: The crude 95% ethanol extract has demonstrated reasonable antioxidant potential. Also, the crude extract, fractions and the volatile oil have shown antimicrobial activity. Lupeol, lupenone and some volatile components have been identified from the leaves. The presence of these compounds may contribute to the bioactivities of the leaf extracts.