Chemoenzymatic synthesis of a new class of macrocyclic oligosaccharides.

A novel and highly efficient chemoenzymatic method has been developed for the preparation of structurally defined macrocyclic oligosaccharides of varied sizes. This method involves chemical or chemoenzymatic synthesis of oligosaccharides containing a galactose at the nonreducing end and a propargyl group at the reducing end as sialyltransferase acceptors. Introducing an azido-containing sialic acid to the nonreducing end of the galactosides through a sialyltransferase-catalyzed enzymatic reaction followed by copper(I)-catalyzed Huisgen's 1,3-dipolar cycloaddition of alkyne and azide provides size-defined macrocyclic carbohydrates. The produced negatively charged macrocycles have high solubility in water and interact with hydrophobic small molecules in a size-dependent manner.