Meroterpenoids isolated from Arnebia euchroma (Royle) Johnst. and their cytotoxic activity in human hepatocellular carcinoma cells.

Six previously undescribed naturally occurring meroterpenoids (2, 5-9) together with seven known meroterpenoids (1, 3, 4, 10-13) were isolated from the root plant of Arnebia euchroma. Their structures and absolute configurations were determined by extensive 1D (1H NMR, 13C NMR) and 2D NMR (1H1H COSY, DEPT, HMQC, HMBC, NOESY) spectroscopic methods, spectroscopy high resolution mass spectrometry, as well as DFT and MM2 force-field calculations. Meroterpenoids 1-13 were evaluated for their cytotoxicities against human liver cancer cell lines SMMC-7721, HepG2, QGY-7703 and HepG2/ADM. Meroterpenoid 5 exhibited the most potent activity with IC50 values of 6.40 ± 0.51, 3.86 ± 0.28, 3.43 ± 0.27 and 11.31 ± 0.67 μM, respectively. Meroterpenoid 4 exhibited significant growth inhibitory effects against HepG2/ADM with IC50 at 18.77 ± 1.23 μM, and meroterpenoid 8 with IC50 at 5.41 ± 0.51 and 6.18 ± 0.47 μM against HepG2 and QGY-7703, respectively. These were more potent than the positive drug, Cisplatin.