Sphaeranthone A, a new carvotacetone from the leaves of Sphaeranthus africanus.

A new carvotacetone sphaeranthone A and four known compounds 3-angeloyloxy-5-[2″,3″-epoxy-2″-methylbutanoyloxy]-7-hydroxycarvotacetone (2), 3-angeloyloxy-5-[3″-chloro-2″-hydroxy-2″-methylbutanoyloxy]-7-hydroxycarvotacetone (3), chrysosplenol D (4), and 3-O-methylquercetin (5) were isolated from leaves of Sphaeranthus africanus growing in Vietnam. Their chemical structures were elucidated by extensive 1D and 2D NMR analysis and high-resolution mass spectroscopy as well as comparisons in literature. Compounds 1-3 were evaluated for the alpha-glucosidase inhibition. They showed moderate activity with IC₅₀ values of 103 ± 1.7, 146.8 ± 2.5, 49 ± 0.8 µg/mL, respectively. [ABSTRACT FROM AUTHOR]