Many polysaccharides existing in nature have branched structures, in which the composition, position, and frequency of branches play key roles in determining the physicochemical and biological properties. However, due to the structural complexity of branched polysaccharides and the difficulty in isolation of pure products, it is challenging to decipher the structures and elucidate the structure-function relationships. Therefore, the synthesis of stereoregular branched polymers that structurally and functionally mimic complex natural polysaccharides are of significant interest. As a conventional method to synthesize branched polysaccharides, cationic ring-opening polymerization of anhydrodisaccharides suffers from the low polymerizability of these disccharide monomers, and thus cannot provide branched polysaccharides with high moleuclar weights. Herein, we report a novel polymerization method to prepare branched polysaccharide mimetics by ring-opening polymerization of a disaccharide-based β-lactam monomer. Using this method, stereoregular poly-amido-saccharides (PASs) bearing α-glucopyranose branches (mal-PASs) are synthesized by anionic ring-opening polymerization of a maltose-based β-lactam followed by debenzylation. The polymerization affords high molecular weight branched polymers (up to 31,510 g/mol) with narrow dispersities (PDI &lt;1.1). The debenzylation of these polymers proceeds smoothly without degradation of the polymer backbone. PASs with different branching frequencies are prepared by copolymerization of maltose β-lactam monomer and glucose β-lactam monomer followed by deprotection. The branching frequencies calculated from nuclear magnetic resonance spectroscopy (NMR) are consistent with the feeding ratio of monomers during copolymerization. Mal-PASs and copolymers are highly soluble in water and adopt a left-handed helical conformation in aqeous solutions, according circular dichroism (CD) analysis. Turbidimetric assays show that, despite the rigid polymer backbone, branched PASs are multivalent ligands to plant lectin Concanavalin A.

Synthesis of biologically active branched polysaccharide mimetics by ring-opening polymerization of a maltose-based β-lactam

256th National Meeting (2018)

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