Construction of triazolyl bidentate glycoligands (TBGs) by grafting of 3-azidocoumarin to epimeric pyranoglycosides via a fluorogenic dual click reaction.

Glycoligands, which feature a glycoside as the central template incorporating Lewis bases as metal chelation sites and various fluorophores as the chemical reporter, represent a range of interesting scaffolds for development of chemosensors. Here, new types of triazolyl bidentate glycoligands (TBGs) based on the grafting of 3-azidocoumarin to the C2,3- or C4,6-positions of three epimeric pyranoglycosides including a glucoside, a galactoside, and a mannoside were efficiently synthesized via a fluorogenic dual click reaction assisted by microwave irradiation. The desired TBGs were afforded in high conversion rates (>90%) and reasonable yields (∼70%). Moreover, a preliminary optical study of two hydroxyl-free glucoside-based TBGs indicates that these compounds are strongly fluorescent in pure water, implying their potential for ion detections in aqueous media.

Variations on the SnCl4 and CF3CO2Ag-promoted glycosidation of sugar acetates: a direct, versatile and apparently simple method with either alpha or beta stereocontrol.

Glycosidation of sugar peracetates (D-gluco, D-galacto) with SnCl(4) and CF(3)CO(2)Ag led to either 1,2-cis-, or 1,2-trans-glycosides, depending primarily on the alcohols used. In particular, 1,2-trans-glycosides, expected from acyl-protected glycosyl donors, were formed in high yields with alcohols sharing specific features such as bulkiness, presence of electron-withdrawing groups or polyethoxy motifs. In contrast, simple alcohols afforded approximately 1:1 mixtures of 2,3,4,6-tetra-O-acetyl, and 3,4,6-tri-O-acetyl 1,2-cis-glycosides due to anomerization and/or acid-catalyzed fragmentation of 1,2-orthoester intermediates. After reacetylation or deacetylation, acetylated or fully deprotected 1,2-cis-glycosides (alpha-D-gluco, alpha-D-galacto) were obtained in approximately 90% yields by a simple and direct method.