Cytotoxic Steroidal Glycosides from the Whole Plant of Calamus acanthophyllus.

A new steroidal glycoside, callaphylloside (1), together with seven known glycosides (2-8), was isolated from the whole plant of Calamus acanthophyllus. The structure of the new compound was elucidated by spectral data analyses and chemical transformations. Compounds 5 and 8 exhibited strong cytotoxic activity against four cancer cell lines (0.7 <= IC50 <= 3.4 mu M). Evaluation of the structure-activity relationship among steroidal glycosides revealed that the structure of spirostanol with an alpha-L-rhamnopyranosyl linked to C-2 of the inner glucopyranosyl residue both play a critical role in the effects of these compounds on the cancer cell lines.