Synthesis of pH-responsive N-acetyl-cysteine modified starch derivatives for oral delivery.

In this study, a novel type of pH-responsive polymer PyHES-NAC (2-hydroxy-3-(2-propynyloxy) propyl hydroxyethyl starch (PyHES)) - (N-acetyl-cysteine (NAC)) was synthesized. First, PyHES was prepared via hydrophobic modification of hydroxyl groups in hydroxyethyl starch (HES) with propynylglycidyl ether (PGE), and then pH-responsive carboxylic acid group was connected to propynyl group via thiol-yne click reaction with NAC. Aqueous PyHES-NAC solutions exhibited a good transference between hydrophobic (or self-assembly) and hydrophilic static along with the change of pH value and protective properties of drugs under acidic conditions. 10.0% DOX was released under artificial gastric fluid after 2 h, whereas an immediate release (above 80%) was observed under artificial intestinal fluid. Drug loading capacity of PyHES-NAC was increased by the increase of degree of substitution (DS) of hydrophobic propynyl groups in PyHES, and 41 wt% DOX Loading capacity was the highest value in our study area.