Protecting group-free introduction of amino acids to polymers through the aza-Michael reaction

The incorporation of natural amino acids onto a silicone framework is efficiently and simply achieved, without protecting groups or solvents, by using aza-Michael addition to acrylate-modified silicones. Amino acids are natural and versatile building blocks that offer inherent biocompatibility, zwitterionic character, and diverse functional groups, making them attractive for a range of applications. Integrating amino acids into materials can enhance biodegradability and biocompatibility – thus enhancing sustainability – due to their natural origin and also allows one to tailor material properties. However, their rich functionality presents challenges during incorporation, often requiring the use of protecting groups and harsher conditions that undermine green chemistry principles. In this study, we present a straightforward strategy for amino acid incorporation using the aza-Michael reaction with cholinium amino acid ionic liquids (ChAAILs). ChAAILs provide a self-solvating and catalyzing environment, eliminating the need for protecting groups and promoting solvent-free synthesis. A kinetic study of aza-Michael reactions between ChAAILs with various small acrylates demonstrated the range of amino acids that can be incorporated and their product stability. ChAAILs exhibit excellent reactivity not only with simple acrylates, but also hydrophilic polyethers and hydrophobic silicones, offering a promising, generic green approach for amino acid-functional polymer modification.