Synthesis of pennogenyl saponins using three methods

The synthesis of pennogenyl saponins using three important methods of glycosylation is reported in this article. Six correlative compounds (7–12) were first synthesized. As donors (1–6), glycosyl halide, trichloroimidate, and thioglycoside were chosen to study their reaction with the acceptor pennogenin. In these reactions the difference in steric hindrance between 3-OH and 17-OH of pennogenin was utilized skillfully and only the 3-hydroxyl group of pennogenin could be connected with each kind of donors selectively. There was no reaction at the 17-hydroxyl group, which had no protection. The characteristic above makes it convenient to synthesize compounds of pennogenyl saponins.