Primary amine and solvent-induced polymerizations of L- or D,L-phenylalanine N-carboxyanhydride

Abstract

Benzylamine, hexylamine and aniline-initiated polymerizations of D,L-phenylalanine and L-phenylalanine N-carboxyanhydride (D,L-Phe-NCA and L-Phe-NCA) were performed in various solvents. The isolated polypeptides were characterized by MALDI-TOF mass spectroscopy. Exclusively linear polypeptides having one amide and one amino endgroup were found, when the polymerizations were conducted in a closed reaction vessel with dioxane or sulfolane as reaction media. Traces of water competed with aniline as initiator, when the reaction vessel was closed with a drying tube. In N,N-dimethylformamide (DMF) formyl endgroups were formed at polymerization temperatures of 60 °C. In DMF and N-methylpyrrolidone, cyclic oligo- and polypeptides were formed by a solvent-induced polymerization initiated by zwitterions, which may compete with the primary amine-initiated polymerizations.