Isolation and Characterization of Methanolic Stem Bark Extracts of Polyalthia longifolia and Root Extract of Annona senegalensis Plants

Abstract

The growing global concern over antimicrobial resistance has prompted intensified research into plant-derived natural products as alternative therapeutic agents. This study aimed to isolate and characterize the bioactive constituents from the methanolic stem bark extract of Polyalthia longifolia and the root extract of Annona senegalensis, two plants widely used in West African ethnomedicine. The crude extracts were subjected to fractionation using column chromatography, employing solvent systems of increasing polarity. The obtained fractions were analysed by Thin Layer Chromatography (TLC) to determine the number of constituent compounds and their retention factor (Rf) values. Characterization of the most active fractions was carried out using Fourier Transform Infrared (FTIR) spectroscopy and Gas Chromatography–Mass Spectrometry (GC-MS). The crude extracts were successfully fractionated resulting in six fractions from each plant. Fractions F1 and F5 from P. longifolia and F3 and F4 from A. senegalensis were selected for detailed phytochemical investigation based on preliminary thin-layer chromatography (TLC) and bioactivity screening. The FTIR spectroscopy revealed the presence of hydroxyl (O-H), carbonyl (C=O), alkyl (C=H), ester (C-O), and aromatic (C=C) groups—consistent with alcohols, flavonoids, phenolics, glycosides, and fatty acids. Gas Chromatography–Mass Spectrometry (GC-MS) analysis further identified a wide range of bioactive compounds. For P. longifolia, major constituents included 2,4-di-tert-butylphenol, methyl palmitate, n-hexadecanoic acid, methyl stearate, and squalene—compounds reported in literature to possess significant antimicrobial, anti-inflammatory, and antioxidant activities. Similarly, the GC-MS profile of A. senegalensis fractions revealed the presence of (+)-roemerine, trans-4-chlorochalcone, hexadecanoic acid, and 9-octadecenoic acid, among others, which have also been associated with broad-spectrum antimicrobial effects. The results validate the ethnomedicinal use of these plants and support their potential as sources of new antimicrobial agents. The combination of FTIR and GC-MS provided a reliable approach to profiling and identifying phytoconstituents in complex plant matrices. These findings not only expand the phytochemical knowledge of P. longifolia and A. senegalensis but also contribute to ongoing efforts in natural product-based drug discovery.