Calosides A-F, Cardenolides from Calotropis gigantea and Their Cytotoxic Activity

Phytochemical analysis of the roots of Calotropis gigantea led to the isolation of six new cardenolide glycosides, calosides A-F (1-6), and five known cardenolides (7-11). The structures of 1-6 were elucidated based on NMR and ECD spectroscopic data interpretation. Caloside D (4) is the first naturally occurring example of a cardenolide containing a C-8/C-19 oxygen bridge. In turn, calosides E (5) and F (6) represent the first naturally occurring 3-epi-cannogenol diglycosides having potent cytotoxicity against the PANG-1 cell line (IC50, 0.081 and 0.070 mu M, respectively) and HeLa (IC50, both 0.17 mu M) cells, under normoglycemic conditions.