Polysaccharide, an almost inexhaustible biomass on Earth, represents one of the most widely used biodegradable and renewable biomaterials. While enzymatic and stepwise glycan assembly methods have been developed to access synthetic polysaccharides for structure-property studies, chemical polymerization strategies for scalable and well-controlled syntheses of native polysaccharides remain elusive.

Based on a reversible deactivation strategy, we developed a chemical approach to precision native polysaccharides via living cationic ring-opening polymerization of anhydrosugars. Using 1,6-anhydrosugars as the monomers, well-defined 1,6-a-polysaccharides with controlled molecular weight, low dispersity, and excellent regio- and stereoselectivity (i.e. 1,6-a-linkage) were readily prepared in the presence of boron trifluoride etherate as a catalyst and glycosyl fluoride as an initiator. We also synthesized precision cellulose (i.e. 1,4-b-linkage) when employing glucose 1,2,4-orthopivalates as the monomers, triflic acid as a catalyst, and dibutyl phosphate as an initiator. Notably, due to the high w-chain end fidelity, we were able to fabricate several block co-polysaccharides that are otherwise challenging to access. Additionally, our method afforded a facile and scalable pathway to multiple biologically relevant precision polysaccharides, including 1,6-a-D-glucan, 1,6-a-L-glucan, 1,6-a-D-mannan, cellulose, and a rare L-cellulose. Furthermore, we demonstrated that the catalytic depolymerization of precision polysaccharides could efficiently regenerate the pristine monomers, suggesting their utility as a class of chemically recyclable materials with tunable thermal and mechanical properties.

Precision native polysaccharides from living polymerization of anhydrosugars

Zhensheng Zhao

Appearances