Facile Organocatalyzed Synthesis of Poly(ε-lysine) under Mild Conditions

Functional poly(amino acid)s such as poly(epsilon-lysine) have many potential high-value applications. However, the effective chemosynthetic strategy for these materials remains a big challenge in polymer chemistry; the key issue is how to design and protect amino groups for the effective ring-opening polymerization (ROP). Our lab succeeded in chemosynthesis of poly(epsilon-lysine) via delicate design of a 2,5-dimethylpyrrole protecting group and metal-catalyzed ROP processes, but harsh reaction conditions (e.g., ca. 260 degrees C) were required. Herein, we developed a superbase t-BuP4-catalyzed ROP of epsilon-lactam derivatives, affording high molecular weight poly(e-lysine) bearing pendant protected amino groups with high monomer conversion (up to 95%). The organocatalytic polymerization could proceed at low reaction temperature (e.g., 60 degrees C) compatible with readily removable protecting groups, providing a sustainable and new methodology toward facile preparation of poly(epsilon-lysine).