Synthesis of pennogenyl saponins via three methods

The pennogenyl saponins(7-12) were synthesized by using three important methods of glycosylation. As donors(1-6), glycosyl halide, trichloroimidate and thioglycoside were chosen to react with the acceptor pennogenin to investigate the results of these reactions. In these reactions the difference of steric hindrance between 3-OH and 17-OH of pennogenin was utilized skillfully and only 3-hydroxyl group of pennogenin could be connected with each kind of donors selectively and there was no reaction at 17-hydroxyl group which had no protection. The characteristic above makes it convenient to synthesize the compounds of pennogenyl saponins.