Iridal-Type Triterpenoids with a Cyclopentane Unit from the Rhizomes of Belamcanda chinensis

Ten new iridal-type triterpenoid derivatives, polycycloiridals K–T (1–10), with a cyclopentane moiety originating from the cyclization of the homofarnesyl side chain were isolated from the rhizomes of Belamcanda chinensis. Their structures were established by spectroscopic data, a single-crystal X-ray diffraction analysis, TDDFT quantum mechanical calculations, and chemical derivatization. Compounds 2 and 10 exhibited 33.4% and 32.9% inhibitory activities, respectively, against PTP1b (protein tyrosine phosphatase) at a concentration of 10 μM. A putative biosynthetic pathway is proposed.