Isolation and characterization of cytotoxic withanolides from the calyx of Physalis alkekengi L. var franchetii.

Phytochemical investigation into the calyx of Physalis alkekengi L. var franchetii (Mast) Makino resulted in the isolation of ten cytotoxic withanolides, including five new withanolides, 1-5. Compounds 2-4 were obtained as epimeric withaphysalins. The new structures were elucidated by extensive spectroscopic analyses and electronic circular dichroism (ECD) calculations. The withanolides were evaluated for their cytotoxic activities against the A549 and K562 cell lines. Compounds 1 and 8 exhibited potent cytotoxic activity against both cell lines with IC50 values of 1.9-4.3 µM and induced typical apoptosis as evaluated by flow cytometric analysis. Further studies indicated that 1 and 8 displayed antitumour effects by suppressing the PI3K-Akt-mTOR signalling pathway.