Synthesis of N-alanyl-hyaluronamide with high degree of substitution for enhanced resistance to hyaluronidase-mediated digestion

In order to increase the resistance of hyaluronic acid towards enzymatic digestion, we prepared N-alanyl-hyaluronamide derivatives using different amidation methods performed either in water, water/acetonitrile mixture or anhydrous dimethylformamide. Our results indicate that amidation of hyaluronic acid in an anhydrous solvent is effective and led to a degree of substitution of the carboxylic groups up to 100%. We also demonstrated the N-alanyl-hyaluronamides present enhanced resistance towards enzymatic digestion while forming solutions with similar viscosities than solutions of hyaluronic acids of similar lengths.