Glycosyl donors glycosidic bonds

Carbohydrate derivatives, in which one or more of the oxygen atoms bonded directly to the carbon skeleton have been replaced by sulfur, are termed thiosugars. The placement of the sulfur atom at the anomeric position constitutes a special case, because thioglycosides, alkyl, aryl and heterocyclic, occupy a very important place as versatile glycosyl donors in glycosidation methodology. Anomeric thiocarbonyl compounds, on the contrary, have been less explored, although their potential and scope is likely to be similar. 

As already observed for azidoglucose-derived donors, glycosylations with azidolactose-derived donors (21f-a-21j-a, Table XXIV) also exhibited high reactivity and/ selectivity (92,114,115,154,161,162). With these results in hand, excellent preconditions for successful syntheses of the Le and Ley antigens have been presented (164,165). Representative examples for the decisive glycoside-bond formations are compiled in Table XXV. Comparison of the results of V-phthaloyl protection and of the azido group does not exhibit advantages for the use of TV-phthaloyl derivatives. 

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