Phyteumosides A and B: New saponins with unique triterpenoid aglycons from Phyteuma orbiculare L.

Phyteumosides A (1) and B (2), two saponins with unprecedented triterpenoid aglycons were isolated from the aerial parts of Phyteuma orbiculare (Campanulaceae). Their structures were elucidated by spectroscopic and chemical methods, and corroborated by X-ray diffraction analyses of the aglycons obtained through enzymatic hydrolysis. The aglycon of 1 can be considered as an incompletely cyclized onoceroid or gammaceroid triterpene with two additional tetrahydropyran rings arising from oxygen bridges. Compound 2 possesses a new 17-polypodene aglycon.