Ent-Kaurane diterpenes from Annona glabra and their cytotoxic activities

A new ent-kaurane glycoside, annoglabasin H (1), and three known ent-kauranes, annoglabasin E (2), annoglabasin B (3), and 19-nor-ent-kaurent-4-ol-17-oic acid (4) were isolated from the fruits of Annona glabra. Their structures were determined by the combination of spectroscopic and chemical methods, including 1D- and 2D-NMR spectroscopy, as well as by comparison with the NMR data reported in the literature. The cytotoxic activities of these compounds were evaluated on four human cancer cell lines, LU-1, MCF-7, SK-Mel2, and KB. Compound 1 exhibited significant cytotoxic activity on all tested human cancer cell lines with IC50 values ranging from 3.7 to 4.6 μM.