Cytotoxic Terpenes from the Flowers of Inula japonica against Human Hepatocarcinoma Cells

Two new 1,10-seco-eudesmanolides (1 and 2) were isolated from the flowers of Inula japonica together with two eudesmanolide analogs (3 and 4) and two monoterpene derivatives (5 and 6). Their structures were established on the basis of detailed spectroscopic analyses and electronic circular dichroism data. All isolates were evaluated for their antiproliferative activities against human hepatocarcinoma HepG2 and SMMC-7721 cells. Japonipene B (3) exhibited the most potent effect with the IC50 values of 14.60±1.62 and 22.06±1.34 μM against HepG2 and SMMC-7721 cells, respectively. Furthermore, japonipene B (3) showed significant efficacies of arresting the cell cycle at the S/G2-M stages, inducing mitochondria-mediated apoptosis, and inhibiting cell migration in HepG2 cells.