Flavonoid Glycosides from Sutherlanida frutescens

Sutherlandia frutescens (L.) R. Br (Fabaceae) is a well-known multipurpose medicinal plant in South Africa that has been widely used as a dietary supplement. Our previous paper has reported the isolation and structure elucidation of four novel cycloartane glycosides from its leaves [1]. Our continuing studies on this medicinally important plant led to the isolation of four new 3-hydroxy-3-methylglutaroyl-containing flavonol glycosides, sutherlandins A–D. Their structures were elucidated by chemical and spectroscopic methods as quercetin 3-O-β-d-xylopyranosyl(1 → 2)-[6-O-(3-hydroxy-3-methylglutaroyl)]-β-d-glucopyranoside (1), quercetin 3-O-β-d-apiofuranosyl(1 → 2)-[6-O-(3-hydroxy-3-methylglutaroyl)]-β-d-glucopyranoside (2), kaempferol 3-O-β-d-xylopyranosyl(1 → 2)-[6-O-(3-hydroxy-3-methylglutaroyl)]-β-d-glucopyranoside (3), kaempferol 3-O-β-d-apiofuranosyl(1 → 2)-[6-O-(3-hydroxy-3-methylglutaroyl)]-β-d-glucopyranoside (4). These compounds, along with the previously isolated triterpene glycosides, have been served as chemical markers for commercial products derived from S. frutescens.

Acknowledgements: The authors thank Mr. Frank T. Wiggers for the assistance in obtaining NMR spectra, and Dr. Charles L. Cantrell for the assistance in GC analysis. This work is supported in part by “The International Center for Indigenous Phytotherapy Studies” funded by NCCAM, grant number 5 U19 AT 003264 and the USDA Agricultural Research Service Specific Cooperative Agreement No. 58-6408-2-0009. References: [1] Fu X, et al. (2008) J Nat Prod, 71: 1749–53.