Primary amine-initiated polymerizations of alanine-NCA and sarcosine-NCA

摘要

Sarcosine-N-carboxyanhydride (Sar-NCA), L-alanine-NCA and D,L-alanine-NCA were polymerized with benzylamine as initiator in three different solvents: dichloromethane (CH2Cl2), 1,4-dioxane and dimethylformamide (DMF). The isolated polyaminoacids were characterized by H-1 NMR spectroscopy and MALDI-TOF mass spectrometry. High conversions and degrees of polymerization (DP) over bars close to the monomer-initiator (M/I) ratios were found for all polypeptides. For polysarcosine which was soluble under the given reaction conditions a narrow monomodal frequency distribution was found. In contrast, a broad frequency distribution was observed, when L-alanine NCA was polymerized in dioxane and DMF. These results were attributed to a partial precipitation of oligopeptides in the beta-sheet structure, which reduces the reactivity of endgroups for steric reasons. The polymerizations of D,L-alanine-NCA showed features in between the extremes of Sar-NCA and L-Ala-NCA.