Incartrilactones A and B: Two schinortriterpenoids with a 14,15-seco-15,17-cyclolancifoartane skeleton from Schisandra incarnata

In this study, incartrilactones A ( 1 ) and B ( 2 ), two previously undescribed schinortriterpenoids (SNTs) possessing an unprecedented 5/5/6/5/7/5-fused hexacyclic skeleton, together with one previously undescribed ( 3 ) and one known ( 4 ) analogues, were isolated from the stems of Schisandra incarnata Stapf. Their structures with absolute configurations were determined by comprehensive spectroscopic analysis, X-ray crystallography and electronic circular dichroism calculation. Compounds 1 and 2 represent the first class of 14,15-seco-15,17-cyclolancifoartane-type SNTs containing the unusual linkage of ‒C14‒C16‒C13‒C17‒C15. The hypothetical biogenetic pathway of compounds 1 and 2 was postulated. Compounds 1 and 2 exhibited potent α -glucosidase inhibitory activity with IC 50 values of 133.1 and 165.3 μM, representing that they were more active than the positive control, acarbose (IC 50  = 232.8 μM). Compound 4 showed moderate in vitro immunosuppressive effect against ConA-induced T cell and LPS-induced B cell proliferation, with IC 50 values of 35.3 ± 0.9 μM and 24.9 ± 0.6 μM, respectively. The cytotoxicity of compounds 1 − 4 against three human cancer cell lines was also tested, with no obvious cytotoxicity being observed.