Ketone Hydrosilylation with Sugar Silanes Followed by Intramolecular Aglycone Delivery: An Orthogonal Glycosylation Strategy

Stereoselective Construction of β-Mannopyranosides by Anomeric O-Alkylation: Synthesis of the Trisaccharide Core of N-linked Glycans

A new and efficient approach for direct and stereoselective synthesis of β-mannopyranosides by anomeric O-alkylation has been developed. This anomeric O-alkylation of mannopyranose-derived lactols is proposed to occur under synergistic control of a kinetic anomeric effect and metal chelation. The presence of a conformationally flexible C6 oxygen atom in the sugar-derived lactol donors is required for this anomeric O-alkylation to be efficient, probably because of its chelation with cesium ion. In contrast, the presence of a C2 oxygen atom plays a minor role. This glycosylation method has been successfully utilized for the synthesis of the trisaccharide core of complex N-linked glycans.

A streamlined strategy for aglycone assembly and glycosylation

Multipurpose sugars: Carbohydrate-derived silane reagents are utilized as the reductant for nickel-catalyzed aldehyde-alkyne reductive coupling reactions and as the glycosyl donor for subsequent intramolecular glycosylation. The approach enables the assembly of the carbon-carbon framework and stereochemical features of an aglycone while simultaneously establishing the site of glycosylation.