Poly(methyl 6-acryloyl-β-d-glucosaminoside) as a Cationic Glycomimetic of Chitosan

Chitosan, a cationic polysaccharide derived from one of the most abundant natural polymers, chitin, has been investigated extensively for its antimicrobial properties. However, it suffers from the inherent drawbacks of natural products such as batch-to-batch variability, limited supply, contamination, and potential adverse reaction. Additionally, its solubility depends on the degree of deacetylation and pH, as it is only soluble under acidic conditions. As an alternative to chitosan, we synthesized the protected cationic glycomimetic monomer methyl N-Fmoc-6-acryloyl-β-d-glucosaminoside from glucosamine. This monomer retains structural features critical to recapitulating the properties of the chitosan repeat unit, namely, the pK_a of the protonated amine. We optimized the free radical polymerization of methyl N-Fmoc-6-acryloyl-β-d-glucosaminoside and fractionated the resultant poly(methyl N-Fmoc-6-acryloyl-β-d-glucosaminoside) to obtain a range of molecular weights. Following Fmoc deprotection, the cationic glycopolymers retained 95% of their expected amine content by mass and exhibited a pK_a of 6.61. Poly(methyl 6-acryloyl-β-d-glucosaminoside) mimicked the molecular weight-dependent bacterial inhibitory property of chitosan in acidic solutions. Importantly, poly(methyl 6-acryloyl-β-d-glucosaminoside) remained soluble at elevated pH (conditions under which chitosan is insoluble) and maintained its antibacterial activity. Mammalian cell viability in the presence of poly(methyl 6-acryloyl-β-d-glucosaminoside) at acidic pH is good, although somewhat lower than viability in the presence of chitosan. No cytotoxic effect was observed at neutral pH. These results demonstrate that poly(methyl 6-acryloyl-β-d-glucosaminoside) is not only a suitable biomimetic for chitosan, but that it can be utilized as an antibacterial agent in a broader range of biologically relevant pHs.