The Flavonoids and Phenolic Acids of the Genus Silphium and Their Chemosystematic Value

The current review outlines the distribution of flavonoids and phenolic acids in eleven species of Silphium (Asteraceae). The chemosystematic significance of these findings is discussed and compared with DNA and morphological-based assignments for eleven species. Special attention is given to the five flavonol triglycosides that were previously isolated and characterized from Silphium species: isorhamnetin 3-O-α-L-rhamnosyl (1″′→6″)-O-β-D-galactopyranoside 7-O-β-L-apiofuranoside (1), quercetin 3-O-α-L-rhamnosyl (1″′→6″)-O-β-D-galactopyranoside 7-O-β-L-apiofuranoside (2), quercetin 3-O-β-L-galactosyl (1″′→6″)-O-β-D-rhamnopyranoside 7-O-α-L-apiofuranoside (3), kaempferol 3-O-β-D-apiofuranoside 7-O-αL-rhamnosyl (1″″→6″′)-O-β-D-galactopyranoside (4) and kaempferol 3-O-β-D-apiofuranoside 7-O-α-L-rhamnosyl (1″″→6″′)-O-βD (2″′-O-E-caffeoylgalactopyranoside) (5). In addition, several other known mono and diglycosidic flavonoids, along with 18 phenolic acids, were also identified and the structures of all of the compounds were established by LC/MS and NMR spectral investigations.