Synthesis and controlled release behaviour of dextran bioactive esters by direct reaction of dextran with the potassium salts of bioactive carboxylic acids

Abstract

AbstractThis work deals with the coupling of model bioactive carboxylic acids (1‐naphthylacetic acid, 2‐(6‐methoxy‐2‐naphthyl)propionic acid (naproxen) and nicotinic acid) to dextran by direct reaction with their potassium salts using pyridine/sulfonyl chloride as activating agent. The structure of the resulting polymeric derivatives was determined by means of 1H and 13C NMR spectroscopy. The influence of the pyridine concentration, the type of sulfonyl chloride and the temperature on the reaction of dextran with potassium 1‐naphthyl acetate was evaluated. The activation energy was found to be 65,7 kJ/mol. 13C NMR spectra at 75,4 MHz of partially modified dextran with 1‐naphthyl acetate groups were studied in order to evaluate the selectivity of the reaction between dextran and potassium 1‐naphthyl acetate. Analysis of the spectra of ring carbons in the anhydroglucose units shows that the reactivity of the individual hydroxyl groups decreases in the order C2 > C4 > C3. The hydrolysis in the heterogeneous phase of some dextran polymers partially modified with 1‐naphthyl acetate groups shows that the release of the bioactive compound is dependent on the hydrophilic character of the polymer as well as the pH value of the medium.