Petersaponins III and IV, triterpenoid saponins from Petersianthus macrocarpus

Two new triterpenoid saponins, petersaponins III and IV (1 and 2), were isolated from an n-butanol extract of the bark of Petersianthus macrocarpus. They possess 21-O-benzoyl-22-O-acetylbarringtogenol C and 21-O-2-furoxyl-22-O-tigloylbarringtogenol C as the aglycon, respectively. For both 1 and 2, the trisaccharide moiety linked to C-3 of the aglycon consists of D-glucuronic acid, D-xylose, and D-galactose, while a L-rhamnose unit is linked to C-28. The structures of 1 and 2 were elucidated by extensive NMR experiments including H-1-H-1 (COSY, HOHAKA, NOESY) and H-1-C-13 (HMQC and HMBC) spectroscopy and by chemical evidence.