Efficient synthesis of alpha- and beta-chacotriosyl glycosides using appropriate donors, and their cytotoxic activity.

Natural steroidal glycosides containing alpha-L-rhamnopyranosyl-(1-->4)-[alpha-L-rhamnopyranosyl-(1-->2)]-beta-D-glucopyranose (chacotriose) at the oligosaccharide moiety exhibit anti-cancer and anti-herpes activities. To investigate the structure-activity relationships of the aglycone parts of chacotriosides, we developed a synthesis method for chacotriosyl glycosides having various aglycones. In the process, it was revealed that alpha-chacotriosyl glycosides could be obtained mainly by using a trichloroacetimidate donor, while beta-chacotriosyl glycosides were afforded by using phosphite and phosphate donors. In cytotoxicity tests using the A549 and HepG2 cell lines, naturally occurring beta-chacotriosyl diosgenin and cholestanol exhibited higher activities than the corresponding alpha-chacotriosyl glycosides.