Powdered stem bark of Lonchocarpus cyanescens was batch extracted with chloroform, methanol and water to yield varying proportions of the extracts: Stem Bark Aqueous Extract (SAE), Stem Methanol Extract (SME) and Stem Chloroform Extract (SCE) respectively. The thin-layer chromatography revealed 5-6 constituents for each extract. The extracts were each washed in a column packed with alumina using n-butanol-glacial acetic acid-water (5:1:4) upper layer and screened for the presence of phytochemicals. The extracts indicated the presence of alkaloids, saponins, tannins, cardiac glycosides, flavonoids and phenols. The ultraviolet-visible (UV-VIS) spectroscopy of SCE showed peaks between 650-776.0 nm, SME between 497.0-795.5 nm and SAE showed bands between 208.5-760.1 nm. The Infrared Spectroscopy (IR) of SCE showed significant broad stretches at 3444.03 cm-1 for the presence of hydrogen bonds (OH), 2932.50 cm-1 C=C of aromatic compounds, 1645 cm-1 for aromaticity and overtoned at 1186 cm-1. The IR of SME showed identical peaks at 3442.09 cm-1. 2931.90 cm-1, 1644.37 cm-1 and 1063.78 cm-1. The IR peaks or bands of SAE appeared at 3431.48 cm-1, 2944.44 cm-1, 1634.73 cm-1 and 1096.57 cm-1. The Gas Chromatography-Mass Spectrometry (GC-MS) of SCE showed a molecular peak (m/z) at 282, SME at 206 and SAE at 256. The antimicrobial activity of the extracts showed sensitivity at a concentration as low as 1.0 × 10-4 mg/mL against four human pathogens; Pseudomonas aeruginosa, Escherichia coli, Salmonella typhi and Staphylococcus aureus. The extracts did not inhibit the growth of Klebsiella pneumonia and Streptococcus pneumonia.
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