Bioactive Pentacyclic Triterpenoids from the Leaves of Cleistocalyx operculatus

Thirteen new pentacyclic triterpenoids, cleistocalyxic acids A-K (1, 2, 4, 5, and 7-13) and cleistocalyxolides A (3) and B (6), and 15 known analogues (14-28), based on taraxastane, oleanane, ursane, multiflorane, and lupane skeletons, were isolated from the leaves of Cleistocalyx operculatus. The structures of 1-13 were elucidated by analysis of their spectroscopic data and ECD/TDDFT computations. Cleistocalyxolide A (3), presumed to be derived from the known taraxastane-type compound 14, has a rare rearranged triterpenoid backbone. Cleistocalyxic acid B (2) displayed cytotoxicity against HepG2, NCI-N87, and MCF-7 cancer cell lines with IC₅₀ values ranging from 3.2 to 6.5 μM, and cleistocalyxic acid D (5) was active against HepG2 and NCI-N87 cells with values around 5.0 μM. The noncytotoxic cleistocalyxic acid E (7) inhibited production of IL-6 by 68.1% and TNF-α by 53.7% in LPS-induced RAW 264.7 macrophages at a concentration of 2 μM.