Saponins from stem bark of Petersianthus macrocarpus.

Two bioactive saponins were isolated from the stem bark of Petersianthus macrocarpus. Their structures were elucidated by chemical degradations and by a combination of 2D NMR techniques and by Californium plasma desorption mass spectrometry. They are 3-O-(beta-D-galactopyranosyl (1-->2)]beta-D-galactopyranosyl (1-->3)]- beta-D-glucuronopyranosyl)-21-O-3-(3-tigloyloxynilic acid)-4-tigloyloxy- alpha-L-arabinopyranosyl] barringtogenol C and 3-O-(beta-D-galactopyranosyl (1-->2)]beta-D-galactopyranosyl (1-->3)]-beta-D-glucuronopyranosyl)-28-O-alpha-L-rhamnopyranosyl barringtogenol C-21-O-benzoate. The absolute configuration of nilic acid was determined by partial synthesis. 3,3'-Dimethoxy ellagic acid and 3,3'-dimethoxy-4-O-beta-D- glucopyranosyl ellagic acid were also isolated.