Influence of methylation process on the degree of quaternization of N-trimethyl chitosan chloride.

N-Trimethyl chitosan chloride (TMC) is a soluble chitosan derivative that shows effective enhancing properties for peptide and protein drug transport across mucosal membranes. TMC was synthesized by reductive methylation of chitosan in an alkaline environment at elevated temperature. The number of methylation process steps and the base used in the process was demonstrated to affect the degree of quaternization of the primary amino group and methylation of 3- and 6-hydroxyl groups. 1H-Nuclear magnetic resonance spectra showed that the degree of quaternization of TMC was higher when using sodium hydroxide as the base compared to using dimethyl amino pyridine. The degrees of quaternization as well as O-methylation of TMC increased with the number of reaction steps. O-Methylation resulted in decreased solubility of TMC. The high degree of quaternization of TMC with a low degree of O-methylation was prepared by employing one reaction step with two subsequent addition steps and a controlled alkaline environment of the mixture reaction.