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

Abstract

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