Potential anticancer agents. Part 13. Cytotoxic constituents of Acanthospermum glabratum(Asteraceae)

Abstract

The Tanzanian plant Acanthospermum glabratum(DC.) Wild (Asteraceae) has yielded nine cytotoxic compounds, seven of which are new sesquiterpene lactones in the melampolide series. Structures of the new compounds were assigned based on spectra comparison with acantholide (3), a compound whose structure was determined by X-ray analysis. New compounds isolated in addition to acantholide (3), were acanthamolide (12), acanthospermolide (1), glabratolide (5), 9-hydroxyglabratolide (6), acanthoglabrolide (7), and dihydroacanthospermal A (10), and the known compounds acanthospermal A (8) and 3,6-dimethoxy-4′,5,7-trihydroxyflavone (15).