Revised structures of four saponins from Nauclea diderrichii

The interglycosidic linkages of four quinovic acid glycosides previously described from the bark of Nauclea diderrichii (de Wild) Merr. (Rubiaceae) are revised on the basis of 2D-NMR spectroscopic results. The structures were established as: quinovic acid 3-O-beta-glucopyranosyl(1-->4)-beta-fucopyranosyl-(28-->1)-beta -glucopyranosyl ester, quinovic acid 3-O-beta-glucopyranosyl-(1-->4)-alpha-rhamnopyranosyl-(28-->1)-beta-glucopyranosyl ester, quinovic acid 3-O-beta-glucopyrnaosyl-(1-->4)-beta-fucopyranoside, and quinovic acid 3-O-beta-glucopyranosyl-(1-->4)-alpha-rhamnopyranoside. The first three saponins are new compounds.