ABSTRACT
Advances in glycobiology have highlighted the critical role played by complex oligosaccharides and glycoconjugates in various biological processes.1 Despite recent progress, access of this class of substances in large quantities is still problematic. In order to make such complex materials ef¥ciently, ready access to saccharidic precursors is required. Among the wide variety of suitable derivatives, propargyl glycosides provide the much needed synthetic versatility. Indeed, besides easy introduction and derivatization of the propargyl aglycone, this function has been described as a stable and versatile anomeric protecting group.2 Propargyl glycosides have also been described as stable glycosyl donors.3 Consequently, they have been used in the synthesis of glycoconjugates,4 oligosaccharides,5 and glycomimetics.6 More recently, these substances have been used as intermediates toward multivalent
Experimental Methods ........................................................................................... 276 General Methods ............................................................................................... 276
Prop-2-Ynyl 2,3,4,6-Tetra-O-Acetyl-α-d-Mannopyranoside (2) ................. 276 Acknowledgments .................................................................................................. 277 References .............................................................................................................. 278
neoglycoconjugates through the CuI-catalyzed Huisgen azide-alkyne 1,3-dipolar cycloaddition (“click chemistry”),7 palladium(0)-catalyzed Sonogashira couplings,8 or organometallic coupling reactions.9 Many methods for the preparation of propargyl glycosides have been described: (1) from reducing sugars by classical Fischer glycosidation,2 (2) from glycosyl donors such as halides10 and trichloroacetimidates,11 and (3) from per-acetylated precursors and propargyl alcohol by Lewis acidcatalyzed glycosidation.12 Here, we describe an improved synthesis of prop-2-ynyl 2,3,4,6-tetra-O-acetyl-α-d-mannopyranoside from d-mannopyranose pentaacetate and propargyl alcohol in the presence of boron tri—uoride-diethyl etherate.
