Synthesis of the α-Linked Digitoxose Trisaccharide Fragment of Kijanimicin: An Unexpected Application of Glycosyl Sulfonates.

Previously, we demonstrated that glycosyl tosylates are effective for the synthesis of ß-glycosides of gluco-configured 2-deoxy sugars. Here, we show the same sulfonate system can be used for the selective synthesis of α-glycosides containing the allo-configured 2-deoxy sugar digitoxose. As with previous work, optimal selectivity is obtained through matching the donor with the appropriate arylsulfonyl chloride promoter. The utility of this method is demonstrated through the synthesis of the α-linked digitoxose trisaccharide fragment of kijanimicin.

Reagent Controlled Direct Dehydrative Glycosylation with 2-Deoxy Sugars: Construction of the Saquayamycin Z Pentasaccharide.

The first synthesis of the pentasaccharide fragment of the angucycline antibiotic saquayamycin Z is described. By using our sulfonyl chloride mediated reagent controlled dehydrative glycosylation, we are able to assemble the glycosidic linkages with high levels of anomeric selectivity. The total synthesis was completed in 25 total steps, and in 2.5% overall yield with a longest linear sequence of 15 steps.