Five undescribed aryltetralin lignans with cytotoxic activities from the fruits of Cleistanthus eberhardtii

Five undescribed lignans, cleiseberharnins A–D (1–4), cleiseberharside A (5) were isolated from the fruits of Cleistanthus eberhartii (Phyllanthaceae), together with six known aryltetralin lignans, cleistantoxin (6), picroburseranin (7), neocleistantoxin (8), 7-hydroxypicropolygamain (9), cleisindoside D (10), and cleisindoside A (11). Their structures and relative configurations were established by analysis of HRESIMS and NMR data, and quantum chemical calculations of JH,H coupling constants. The absolute configurations of 1–5 were determined by analysis of their experimental CD spectra and comparison with calculated electronic circular dichroism (ECD) spectra. All compounds (1−11) were evaluated for their cytotoxicity against KB, MCF-7, HepG-2, and Lu-1 human cancer cell lines. Among the tested compounds, compounds 6 and 7 showed strong activity against KB, MCF7, HepG2 and Lu-1 cell lines with IC50 values in the range of 0.02–0.62 μM. Compound 1 showed activity against three cancer cell lines KB, HepG2, and Lu-1 with IC50 values of 6.98, 7.61 and 11.75 μM, respectively. Compound 2 exhibited a selective inhibition with moderate cytotoxicity against Lu-1 with IC50 value of 15.30 μM. Compounds 4, 5 and 9 showed moderate activity against the three cancer cell lines with IC50 values in the range of 8.73–19.70 μM.