4 - Synthesis and Activation of Carbohydrate Donors: Thioglycosides and Sulfoxides

Abstract

The successful application of a protecting group for temporarily masking the anomeric centre in a carbohydrate building block during oligosaccharide synthesis depends on its stability to various reaction conditions as well as its amenability to straight forward chemoselective transformations when necessary. An alkyl-or arylthio group placed at the anomeric centre satisfies most of these requirements; it is, therefore, of no surprise that thioglycosides are amongst the most popular classes of glycosyl donor compounds employed in oligosaccharide synthesis. Several reviews on the use of thioglycosides have appeared over the past decade, most of them dealing mainly with methods for activating thioglycosides in oligosaccharide assembly. While these reviews summarize methods available for the preparation as well as activation of thioglycosides, practical aspects have not been covered in any detail. This chapter is designed to fill this gap in particular, and provides a perspective of reliable practical methods available from the literature to date. In addition, as thioglycosides form valuable precursors for glycosyl sulfoxides, preparation and activation of the latter are also described.