Bioactivity Guided Isolation of Gallic Acid and Kaempferol-7-O-Glucoside from Ethyl Acetate Fraction of Entada africana Guill. & Perr. Stembark Crude Extract

Abstract

Medicinal plants have historically played a crucial role in human healthcare due to their phytochemical compounds which provides protection against various pathogens and environmental challenges. The aim of the study was the isolation of bioactive compounds from Entada africana; a plant recognized for its medicinal properties in Africa. The stembark extract of Entada africana was obtained using maceration and fractionated. The fractions were evaluated for antibacterial activities using agar disc diffusion method and the antioxidant activities of the most active fraction (ethyl acetate) was evaluated using ferric reducing antioxidant power (FRAP), ferric ion chelating activity (FICA) and hydrogen peroxide assay (H2O2). Gradient elution on column chromatography was used to obtain pure isolates. The isolates were characterized using FT-IR, NMR and in comparison with literature. The extraction process yielded 165g of extract from which 11.4 g was obtained from the ethyl acetate fraction. The ethyl acetate extract had inhibition zones of 13.53 mm for Salmonella typhi, 11.00 mm for Enterococcus faecalis, and 10.67 mm for Klebsiella pneumoniae. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) for the ethyl acetate extract suggests moderate non-bactericidal activity against Salmonella typhi, and weak on other pathogens in the study. Antioxidant assays revealed IC50 values of 7.78 µg/ml for FICA, 33.73 µg/ml for FRAP assay, and 16.60 µg/ml for H2O2 scavenging activity; all indicating extract’s strong ability to scavenge free radicals. The characterization of P43 and P17 based on spectroscopic data and literature comparison suggests P43 as gallic acid while P17 as kaempferol-7-O-glucoside. While gallic acid had been previously reported, this is the first time kaempferol-7-O-glucoside is being reported from the stem bark extract of Entada africana. Both compounds had in previous studies demonstrated remarkable antibacterial and antioxidant properties. The study therefore supports the traditional medicinal uses of Entada africana.