Isolation of an antibacterial sesquiterpenoid from Warburgia salutaris

The bark of Warburgia salutaris is used in traditional medicine as an expectorant and smoked for coughs and colds, including a topical application for sores and inflammation. A previous screening of South African medicinal plants showed that this plant had promising antibacterial activity. Subsequently, this endangered tree species was selected for bioassay-guided fractionation in order to identify the active principles. Fractionation of the ethyl acetate extract of the stem bark by chromatographic techniques yielded a sesquiterpenoid which exhibited antimicrobial activity against Gram-positive bacteria. The compound, muzigadial, has previously been reported in two other Warburgia species, this being the first time it has been reported from W. salutaris. Muzigadial had minimum inhibitory concentration values ranging from 12.5 to 100 microg ml(-1).