A New Carvotacetone Derivative from the Aerial Part of Sphaeranthus africanus.

Sphaeranthus africanus L. is native in Vietnam. Little is known about alpha-glucosidase inhibition of Sphaeranthus africanus and its isolated compounds. A bioactive-guided isolation was applied to the Vietnamese Sphaeranthus africanus to find alpha-glucosidase inhibitory components. Eight compounds were detected and structurally elucidated. They are 3-angeloyloxy-5-[2″,3″-epoxy-2″-methylbutanoyloxy]-7-hydroxycarvotacetone, 3-angeloyloxy-5-[3″-chloro-2″-hydroxy-2″-methylbutanoyloxy]-7-hydroxycarvotacetone, 3-angeloyloxy-5-[2″R,3″R-dihydroxy-2″-methyl-butanoyloxy]-7-hydroxycarvotacetone, 3-angeloyloxy-5-[2″S,3″R-dihydroxy-2″-methyl-butanoyloxy]-7-hydroxycarvotacetone, 3-angeloyloxy-5-[2″S,3″S-dihydroxy-2″-methyl-butanoyloxy]-7-hydroxycarvotacetone, 5-angeloyloxy-7-hydroxy-3-tigloyloxycarvotacetone, 3-O-methylquercetin, and chrysosplenol D. Their chemical structures were elucidated by extensive 1D and 2D NMR analysis and high-resolution mass spectroscopy as well as comparisons in literature. 3-Angeloyloxy-5-[2″S,3″S-dihydroxy-2″-methyl-butanoyloxy]-7-hydroxycarvotacetone is a new compound. Isolated compounds were evaluated for the alpha-glucosidase inhibition. Isolated compounds showed moderate activity with IC50 values ranging from 128.9-274.3 µM while others are weak. A molecular docking study was conducted, indicating that isolated compounds are potent alpha-glucosidase inhibitory compounds.