HATU Coupling for Fast, Efficient, and Selective N-acylation of chitosan: DoE-optimized synthesis of cationic...

Chitosan is a cationic polysaccharide valued in biomedicine for its biodegradability, biocompatibility, non-toxicity, and antimicrobial activity. However, its poor solubility and aggregation tendency limit its applications. These issues can be addressed through chemical modification, which also enhances biological properties. Common acylation and alkylation methods often lack efficiency and control over the degree of substitution (DS). Here, a new N-acylation procedure using hexafluorophosphate azabenzotriazole tetramethyl uronium (HATU) as coupling agent in dimethyl sulfoxide (DMSO) is reported. The study focused on synthesizing a cationic betaine N-acyl chitosan derivative, N-(2-(N,N,N-trimethylammoniumyl)acetyl) chitosan (TAC), optimized through a Design of Experiments (DoE) approach to achieve full DS control. Two 12-experiment full factorial DoE optimizations were conducted, varying equivalent ratios of betaine, HATU, 1-hydroxybenzotriazole (HOBt), and triethylamine (TEA). The DS of the TAC products was determined by NMR. The optimized procedure allowed for the quantitative conjugation of betaine, using a slight excess of HATU, requiring only 3 h to complete the synthesis of the TAC derivative from chitosan starting material. The procedure was successfully used for the synthesis of mixed phenylpropionyl-, cinnamoyl- and feruloyl-TAC chitosan derivatives, but further development may be needed for more general applicability. Antibacterial assay confirmed of TAC antibacterial activity, tested against Staphylococcus aureus.