An unusual indole-diterpenoid with C-17 norcassane skeleton from Euphorbia fischeriana induces HEL cell cycle arrest and apoptosis

Two new polycyclic diterpenoids, euphkanoids H and I (1 and 2), along with 6 known analogues (2-8) were isolated from the roots of Euphorbia fischeriana, a traditional Chinese medicine. Their structures were identified by spectral methods, and the absolute configurations of 1 and 2 were determined by ECD calculation and single crystal X-ray diffraction, respectively. Compound 1 represents the first example of C-17 norcassane indole-diterpenes. All the isolates were screened for antiproliferative activity against a panel of human cancer cell lines using the MTT assay, and 1 showed significant cytotoxicity against HEL cells (IC50 = 3.2 μM). Simple mechanistic study revealed that 1 could induce cell cycle arrest at G0/G1 phase and apoptosis in HEL cells.