Biological activities and syntheses of steroidal saponins: the shark-repelling pavoninins

Steroidal saponins are complex compounds that have a steroid attached to a carbohydrate moiety. They are natural surfactants and detergents and exhibit a number of biological effects. Steroidal saponins have shown membrane-permeabilizing, hypocholesterolemic, immunostimulant, and anticancer properties. They have also been found to affect the growth, food intake and reproductive capabilities of animals. Furthermore, they have been shown to act as antiviral and antifungal agents. They have been isolated from many plants and some animals, especially sea cucumbers and starfish. Fish belonging to the species Pardachirus pavoninus excrete a mixture of six steroidal N-acetylglucosaminides, pavoninins 1-6, with shark-repelling properties. We report syntheses of the C-15 alpha pavoninin-4 by both direct synthesis from diosgenin and by remote functionalization. A general solution for the glycosylation of hindered alcohols was developed using glycosyl fluorides as good glycosyl donors. The syntheses of two C-16 beta structural analogs of OSW-1 are described.