Isolation of an antibacterial stilbene from Combretum woodii (Combretaceae) leaves

Abstract

Acetone extracts of C. woodii leaf powder was separated by solvent-solvent partition into six fractions. The highest total activity was in the chloroform fraction. This fraction contained mainly one compound active against S. aureus. This compound was isolated by bioassay-guided fractionation using silica gel open column chromatography and identified by nuclear magnetic resonance (NMR) and mass spectroscopy (MS) as the stilbene 2’,3’,4-trihydroxyl-3,5,4’-trimethoxybibenzyl (combretastatin B5) previously isolated from the seeds of C. kraussii. It showed significant activity against S. aureus with
an MIC of 16 mg/ml but with lower activity towards P. aeruginosa (125 mg/ml), E. faecalis (125 mg/ml) and slight activity against E. coli. This is the first report of the antimicrobial activity of combretastatin B5. Its concentration in the leaves was in the order of 5-10 mg/g which makes the use of non-polar leaf
extracts a viable proposition in treating some infections, particularly in resource-poor settings.