Phyteumosides A and B: New Saponins with Unique Triterpenoid Aglycons from <i>Phyteuma orbiculare</i> L.

Phyteumosides A (<b>1</b>) and B (<b>2</b>), two saponins with unprecedented triterpenoid aglycons, were isolated from the aerial parts of <i>Phyteuma orbiculare</i> (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 <b>1</b> can be considered as an incompletely cyclized onoceroid or gammaceroid triterpene with two additional tetrahydropyran rings arising from oxygen bridges. Compound <b>2</b> possesses a new 17-polypodene aglycon.