Semisynthesis and characterization of versatile azide intermediates using sodium alginate and its homopolymeric derivatives as starting material

Abstract

Alginate, a polyuronic biopolymer composed of mannuronic and guluronic acid units, contain hydroxyl and carboxyl groups as targeting modification sites to obtain structures with new and/or improved biological properties. The copper-catalyzed azide-alkyne cycloaddition (CuAAC) is a versatile click reaction for polymer functionalization, but it typically requires a “pre-click” modification to introduce azide or alkyne groups. Here, we described a straightforward chemical path to selectively modify alginate carboxyl groups producing versatile azido derivatives through N-acylation using 3-azydopropylamine. The resulting azide-functionalized polysaccharides underwent click chemistry to yield amino derivatives, confirmed by NMR and FTIR analyses. The 1H NMR spectrum reveals a characteristic triazole group signal at 8.15 ppm. The absence of the azide FTIR band for all amino derivatives, previously observed for the N-acylation products, indicated reaction success. Antibacterial and antioxidant assessments revealed that the initial polysaccharide lacks E. coli inhibition, while the click chemistry-derived amine products exhibit growth inhibition at 5.0 mg/mL. Lower molecular weight derivatives demonstrate superior DPPH scavenging ability, particularly amino-derivatives (24–33 % at 1.2 mg/mL). This innovative chemical pathway offers a promising strategy for developing polysaccharide structures with enhanced properties, demonstrating potential applications in various fields.