Synthesis of N,N-dimethyl N-ethyl chitosan as a carrier for oral delivery of peptide drugs

N,N-dimethyl N-ethyl chitosan (DMEC), a quanternized derivative of chitosan was synthesized based on a modified two-step method via a 21 factorial design to optimize the preparative conditions. The degree of deacetylation of the starting chitosan was determined by FTIR and NMR methods and was 95%. In the first step of the synthesis, mono-ethyl chitosan was prepared by introducing an ethyl group onto the amine group of chitosan via a Schiff base and in the next step methyl iodide was added to produce DMEC which was water soluble in a pH range of 4-8. The DMEC polymers with different degrees of quaternization were obtained and fully characterized using FTIR and H-1-NMR spectroscopic methods. Based on H-1-NMR calculations, the degree of quaternization was 52% by optimizing the two-step process.