Glycosides of polygalacic acid from the stem barks of Piper guineense Schum and Thonn

In a continuation of our study on constituents of P. guineense now focusing on the search for saponins, phytochemical investigation of the n-BuOH fraction of P. guineense stem bark led to the isolation of three previously undescribed triterpenoid saponins, named guineenosides A─C (1─3). Their structures were established on the basis of extensive analysis of 1D and 2D NMR (¹H, ¹³C NMR, DEPT, COSY, TOCSY, NOESY, HSQC, HSQC-TOCSY and HMBC) and HRESIMS experiments, and by chemical evidence as 3-O-{α-L-rhamnopyranosyl-(1 → 3)-β-D-xylopyranosyl-(1 → 2)-α-L-arabinopyranosyl-(1 → 4)-α-L-rhamnopyranosyl-(1 → 3)-[α-L-arabinofuranosyl-(1 → 4)]-α-L-rhamnopyranosyl-(1 → 3)-β-D-fucopyranosyl} polygalacic acid 28-O-α-L-rhamnopyranosyl-(1 → 4)-α-L-rhamnopyranosyl-(1 → 3)-β-D-xylopyranosyl ester (1), 3-O-{α-L-rhamnopyranosyl-(1 → 3)-β-D-xylopyranosyl-(1 → 2)-α-L-arabinopyranosyl-(1 → 4)-α-L-rhamnopyranosyl-(1 → 3)-[α-L-arabinofuranosyl-(1 → 4)]-α-L-rhamnopyranosyl-(1 → 3)-β-D-fucopyranosyl} polygalacic acid 28-O-β-D-glucopyranosyl-(1 → 3)-α-L-rhamnopyranosyl-(1 → 4)-α-L-rhamnopyranosyl-(1 → 3)-β-D-xylopyranosyl ester (2), and 3-O-{α-L-rhamnopyranosyl-(1 → 2)-β-D-xylopyranosyl-(1 → 3)-β-D-fucopyranosyl} polygalacic acid 28-O-[α-L-rhamnopyranosyl-(1 → 4)-α-L-rhamnopyranosyl-(1 → 3)-β-D-xylopyranosyl ester (3). This is the first report of triterpenoid saponins from P. guineense.