Synthesis and Characterization of Norbornene-Modified Hyaluronic Acid

Nor-HA was prepared as previously described.^{[26 (link)]} Briefly, HA modified with tetrabutylammonium salt was dissolved in anhydrous dimethyl sulfoxide (DMSO). Dimethyl aminopyridine, norbornene-2-carboxylic acid, and di-tert-butyl dicarbonate were added to the DMSO and allowed to react overnight at 45 °C. The reaction was quenched with an equal volume of cold water, and the Nor-HA product was then dialyzed for 14 days in DI water, frozen, lyophilized until dry, and stored at −20 °C until further use. To determine the degree of modification of the HA backbone with norbornene functional groups, lyophilized polymer were dissolved in deuterium oxide at a concentration of 10 mg mL⁻¹ and analyzed using ¹H NMR (Bruker NEO400).