Flavonol Glycosides from the South African Medicinal Plant Sutherlandia frutescens

Phytochemical investigation of the leaves of Sutherlandia frutescens led to the isolation of four new 3-hydroxy-3-methylglutaroyl-containing flavonol glycosides, sutherlandins A-D (1-4). Their structures were elucidated by chemical and spectroscopic methods as quercetin 3-O-beta-D-xylopyranosyl(1 -> 2)-[6-O-(3-hydroxy-3-methylglutaroyl)]-beta-D-glucopyranoside (1), quercetin 3-O-beta-D-apiofuranosyl(1 -> 2)-[6-O-(3-hydroxy-3-methylglutaroyl)]-beta-D-glucopyranoside (2), kaempferol 3-O-beta-D-xylopyranosyl (1 -> 2)-[6-O-(3-hydroxy-3-methylglutaroyl)]-beta-D-glucopyranoside (3), and kaempferol 3-O-beta-D-apiofuranosyl(1 -> 2)-[6-O-(3-hydroxy-3-methylglutaroyl)]-beta-D-glucopyranoside (4).