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Abstract 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-15α 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-16β structural analogs of OSW-1 are described.
Keywords Biological activities * Steroidal * Saponin * Aglycone * Sterol * Monosaccharide * Glycoside * Synthesis * Pavoninin * OSW-1
Abbreviations
AgF Silver fluoride
AgOTf Silver triflate
Bn^sub 8^Sn^sub 4^Cl^sub 4^O^sub 2^ Bisdibutylchlorotin(IV) oxide
DAST (Diethylamino)sulfur trifluoride
DDQ 2,3-Dichloro-5,6-dicyano-1, 4-benzoquinone
DEAD Diethyl azodicarboxylate
DIAD Diisopropyl azodicarboxylate
DMSO Dimethyl sulfoxide
LAH Lithium aluminum hydride
LiDBB Lithium di-tert-butylbiphenyl
MsCl Methanesulfonyl chloride
Piv Pivaloyl
TBAF Tetrabutylammonium fluoride
TBSO t-Butyldimethylsilyloxy
Introduction
Steroidal saponins constitute a structurally and biologically diverse class of glycoconjugates, which have been isolated from a wide variety of both plant and animal species [1-3]. They consist of a hydrophobic aglycone (sapogenin) to which a sugar moiety is attached, usually containing a glucose, galactose, N-acetylglucosamine, glucuronic acid, xylose, rhamnose or methylpentose. The oligosaccharide is normally attached at the C-3 position but many are now known that have it attached at C-6,7,15,16,24, and 26. In this review we will survey some of the biological properties of saponins and report methods for the synthesis of 15α and 16β steroidal saponins.
Steroidal saponins are natural surfactants, or detergents. They have been isolated from a great number of terrestrial plants, such as alliums, asparagus, aubergine, capsicum peppers, oats, tomato seeds, yams, and ginseng [2]. They are most abundant in the desert plants Yucca and Quillaja. They are common in plants used as herbs or for their health-promoting properties. Steroidal saponins are uncommon animal...