Bioactive Polyphenolic and Terpenoid Compounds from Stem Bark and Flowers of Terminalia brownii

Terminalia brownii Fresen (Combretaceae) extensively used in Eastern, Southern, and Western Africa herbal remedies in treatment of variety of diseases including liver cirrhosis. Bioassay – guided fractionation was used to isolate the compounds responsible for these actions.

The study sought to extract, characterize and determine the antimicrobial activities of the components of the commonly used stem bark and hitherto uninvestigated regeneratable flowers of T.brownii.

Column chromatography was used to fractionate and isolate the compounds followed by thin layer chromatography. The isolates were structurally elucidated using FTIR, ¹H NMR, ¹³C NMR and HRESI-MS spectral data. The isolated compounds' antimicrobial activities were evaluated against Candida albicans, Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli.

Bioassay – guided fractionation of methanol and 50% dichloromethane: methanol extracts of Terminalia brownii stem bark and flowers yielded seven known metabolites; termiglaucescin (1), arjunglucoside-I (2), sericoside (3), 23-galloyl arjungenin (4), 28-O-β-D-glucopyranosyl-2,3,6-trihydroxy-23-galloylolean-12-dien-28-oate (5), 3,3',4',5-tetrahydroxy-7-methoxyflavone (9), 3,3',4',5,7-pentahydroxyflavone (10) and three new metabolites: 1,4,7-tri-O-galloyl hept-6-deoxyheptose (6), 1,2,4-tri-O-galloyl-8,9-dideoxynonose (7), Rhamnetin-3-O-(2,3,6-trigalloyl)-β-D-glucopyranoside (8). Among these molecules, compound (6) was extremely potent toward E. coli (16.5±0.7 mm) while (1) showed substantial inhibitory effects on Candida albicans (16.0±5.7 mm). Compounds 6, 7, 8, 9, and 10 were extracted and identified for the first time from 50% dichloromethane/methanol flower extract. The extract yielded three novel bioactive compounds (6, 7 and 8) that shown substantial activity on P.aeruginosa, E. coli, C. albicans, S. aureus.

For the first time, the results of this investigation demonstrate that flower extract possess strong antibacterial and antifungal qualities, akin to those of stem bark extract. As a result, more environmentally friendly flower extracts should be considered for treatment of bacterial and fungal infection.