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 AC (13). 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-{alpha-L-rhamnopyranosyl-(1 -> 3)-beta-Dxylopyranosyl-(1 -> 2)-alpha-L-arabinopyranosyl-(1 -> 4)-alpha-L-rhamnopyranosyl-(1 -> 3)-[alpha-L-arabinofuranosyl-(1 -> 4)]-alpha-L-rhamnopyranosyl-(1 -> 3)-beta-D-fucopyranosyl} polygalacic acid 28-O-alpha-L-rhamnopyranosyl-(1 -> 4)-alpha-Lrhamnopyranosyl-(1 -> 3)-beta-D-xylopyranosyl ester (1), 3-O-{alpha-L-rhamnopyranosyl-(1 -> 3)-beta-D-xylopyranosyl-(1 -> 2)-alpha-L-arabinopyranosyl-(1 -> 4)-alpha-L-rhamnopyranosyl-(1 -> 3)-[alpha-L-arabinofuranosyl-(1 -> 4)]-alpha-L-rhamnopyranosyl-(1 -> 3)-beta-D-fucopyranosyl} polygalacic acid 28-O-beta-D-glucopyranosyl-(1 -> 3)-alpha-L-rhamnopyranosyl(1 -> 4)-alpha-L-rhamnopyranosyl-(1 -> 3)-beta-D-xylopyranosyl ester (2), and 3-O-{alpha-L-rhamnopyranosyl-(1 -> 2)-beta-Dxylopyranosyl-(1 -> 3)-beta-D-fucopyranosyl} polygalacic acid 28-O-[alpha-L-rhamnopyranosyl-(1 -> 4)-alpha-L-rhamnopyranosyl-(1 -> 3)-beta-D-xylopyranosyl ester (3). This is the first report of triterpenoid saponins from P. guineense.

Automated summary

This study identified three previously undescribed triterpenoid saponins from P. guineense, marking a new discovery in the field.