A new highly oxygenated ent-atisane diterpenoid, namely excagallonoid A (1), together with five known analogues (2 - 6) were isolated from the leaves and twigs of Excoecaria agallocha. Their structures were elucidated on the basis of extensive spectroscopic analyses (HRESIMS, UV, IR, 1 D and 2 D NMR), and the absolute configurations of 1 and 5 were determined by single-crystal X-ray diffraction. Compound 1 represents the first example of an ent-atisane diterpenoid featuring a vicinal 2,3-diol moiety. Compounds 1 and 4 exhibited weak cytotoxicities in vitro against RKO colon cancer cells with IC50 values of 28.7 ± 1.98 and 32.6 ± 2.81 µM, respectively.
Keywords: Excoecaria agallocha; cytotoxicity; ent-atisane diterpenoid; podocarpane diterpenoid.