Precision native polysaccharides from living polymerization of anhydrosugars

The composition, sequence, length, and type of glycosidic linkages of polysaccharides profoundly affect their biological and physical properties. However, investigation of the structure-function relationship of polysaccharides is hampered by accessing well-defined polysaccharides in sufficient quantities. Here, we report a chemical approach to precision polysaccharides with native glycosidic linkages via living cationic ring-opening polymerization of 1,6-anhydrosugars. We synthesized well-defined polysaccharides with tunable molecular weight, low dispersity, and excellent regio- and stereoselectivity using a boron trifluoride etherate catalyst and glycosyl fluoride initiators. Computational studies revealed that the reaction propagated through the monomer alpha-addition to the oxocarbenium and was controlled by the reversible deactivation of the propagating oxocarbenium to form the glycosyl fluoride dormant species. Our method afforded a facile and scalable pathway to multiple biologically relevant precision polysaccharides, including D-glucan, D-mannan, and an unusual L-glucan. We demonstrated that catalytic depolymerization of precision polysaccharides efficiently regenerated monomers, suggesting their utility as a class of chemically recyclable materials with tailored thermal and mechanical properties.