Structures and biological activities of plant glycosides:: cholestane glycosides from Ornithogalum saundersiae, O-thyrsoides and Galtonia candicans, and their cytotoxic and antitumor activities

Systematic phytochemical screening of higher plants using a cytotoxicity-guided fractionation procedure resulted in the isolation from the bulbs of Ornithogalum saundersiae (Liliaceae) an acylated cholestane diglycoside, 17 alpha-hydroxy-16 beta-[(O(2-O-p-methoxybenzoyl-beta-D-xylopyranosyl)-(1 -> 3)-2-O-acetyl-alpha-L-arabinopyranosyl)oxy]cholest-5-en-22-one, tentatively named OSW-1. In vitro cytotoxic and in vivo antitumor screening of OSW-1 revealed that it is a possible candidate as a novel anticancer agent. Furthermore, more than 20 OSW-1-related Compounds were isolated, not only from the bulbs of O. saundersiae, but also from those of O. thyrsoides and Galtonia candicans, which are taxonomically related to O. saundersiae. In vitro cytotoxic evaluation of all the isolated compounds and their semi-synthetic analogues allowed the structure-activity relationships of the OSW-I derivatives to be established. In addition, these three plants were found to produce a series of novel cholestane glycosides with a new rearranged side-chain moiety, 24(23 -> 22)abeo-cholestane, some of which showed potent cytotoxic activity against HL-60 leukemia cells.