Photosensitive Fluorous Tag-Assisted Convergent Synthesis of β-1,4-Mannuronates.

Rapid synthesis of saccharides by a chemical method is an efficient way to meet the demand for well-defined glycans to probe their biological functions. Herein, a feasible and convenient strategy for saccharide synthesis was established by introducing a photosensitive fluorous tag at the anomeric position of glycosides. The tag was used not only in polytetrafluoroethylene-assisted rapid purification but also as a temporary protecting group at the reducing end of carbohydrates. The tag-protected glycosides could be transformed into new glycosyl donors for convergent synthesis after orthogonal deprotection of the tag by photolysis. Via combination of the β-directing C-5 carboxylate glycosylation strategy, β-1,4-mannuronates were efficiently prepared.