Reactive norbornene- and phenyl carbonate-modified dextran derivatives: A new approach to selective functionalization

Abstract

Polysaccharides containing norbornene moieties are gaining importance in biomedical applications. This study presents the effective linkage of the norbornene moiety to the polysaccharide backbone using dextran phenyl and p-nitrophenyl carbonates as activated starting biopolymer derivatives. A novel norbornene-functionalized dextran with a degree of substitution of 1.0 predominantly modified at position 2 could be obtained by aminolysis of the dextran p-nitrophenyl carbonate. A highly norbornene-functionalized dextran derivative is derived from the reaction with dextran phenyl carbonate. The reactivity of these norbornene-functionalized derivatives was investigated, demonstrating a complete conversion of the norbornene moiety in radical thiol-ene reactions while maintaining the stability of the carbamate bond. The synthesis of mixed dextran derivatives containing reactive phenyl carbonate- and norbornene moieties is also described. The selectivity of reactions involving phenyl carbonates with amines and thiols was assessed, revealing a cleavage of phenyl carbonate moieties, which is influenced by the basicity of the amine rather than side reactions with thiols. NMR spectroscopy and elemental analysis were employed to accurately determine the degrees of substitution and confirm the structural integrity of the derivatives.