Bibenzyls and dihydroisocoumarins from white salsify (Tragopogon porrifolius subsp porrifolius)

A phytochemical investigation of three accessions of Tragopogon porrifolius L. subsp. porrifolius (Asteraceae, Lactuceae) yielded three new bibenzyl derivatives, 5,4'-dihydroxy-3-alpha-(L)-rhamnopyranosyl-(1-3)-beta-(D)-xylopyranosyloxybibenzyl, 2-carboxyl-3,4'-dihydroxy-5-beta-(D)-xylopyranosyloxybibenzyl, tragopogonic acid (2'carboxyl-3',5',4"-trihydroxyphenylethanone) and three dihydroisocoumarin derivatives, including the new natural product 6-O-methylscorzoereticoside 1. One of the isolated bibenzyl derivatives is considered to be a precursor to the biosynthesis of dihydroisocoumarins. Structures of new compounds were established by HR mass spectrometry, extensive 1D and 2D NMR spectroscopy, and CD spectroscopy. Moreover, radical scavenging activities of the polyphenolic compounds were measured using the 2,2-diphenyl-l-picrylhydrazyl assay; two of the bibenzyls showed moderate and two of the dihydroisocoumarins showed weak radical scavenging activities. The chemosystematic impact of bibenzyls and dihydroisocournarins is discussed briefly. (c) 2005 Elsevier Ltd. All rights reserved.