Euphorins A-H: bioactive diterpenoids from Euphorbia fischeriana

Phytochemical investigation of the roots of Euphorbia fischeriana resulted in the isolation of 23 diterpenoids (1–23), which were classified into five subtypes, namely, ent-rosane (1–9), ent-abietane (10–16), ent-kaurane (17), ingenane (18–22), and lathyrane (23). The chemical structures of eight new compounds, namely, euphorin A (4), B (5), C (7), D (9), E (13), F (14), G (15), and H (16), were elucidated on the basis of extensive 1D and 2D NMR spectroscopic analyses, as well as single crystal X-ray structure analysis. A number of compounds (2, 6, 7, 10, 11, 13, 16, 19, 20, 22, and 23) showed inhibitory activity on the formation of mammospheres in human breast cancer MCF-7 cells at a final concentration of 10 μM, suggesting the potential of these bioactive diterpenoids for further investigation of the action targeting cancer stem cells.