Investigation of α-amino acid N-carboxyanhydrides by X-ray diffraction for controlled ring-opening polymerization

• Published in: Tetrahedron letters 2019-01, Vol.60 (3), p.272-275
• Main Authors: Schäfer, Olga, Schollmeyer, Dieter, Birke, Alexander, Holm, Regina, Johann, Kerstin, Muhl, Christian, Seidl, Christine, Weber, Benjamin, Barz, Matthias
• Format: Article
• Language: English
• Subjects: Crystal structure; Melting point; Monomer purity; Ring-opening polymerization; α-Amino acid N-carboxyanhydrides
• ISSN: 0040-4039; 1873-3581
• DOI: 10.1016/j.tetlet.2018.12.028

[Display omitted] •Correlating crystal structure and melting point of α-amino acid N-carboxyanhydrides.•Single-crystal properties (e.g. retained stereo-chemistry during synthesis) of NCAs.•Melting points of NCAs should be evaluated as a standard for monomer purity.•Pure NCA monomers can be polymerized under controlled conditions. The need for a scalable synthesis of not sequence defined polypeptides as biomaterials is met by the ring-opening polymerization of α-amino acid N-carboxyanhydrides (NCAs). Even though this polymerization technique appears straight forward, it holds pitfalls in terms of reproducibility and overall control over the polymerization conditions, which depends, beside choice of solvent or initiator, significantly on reagent purity. In addition, the synthesis of monomers can lead to the formation of racemic amino acids. Thus, in this work, we describe the benefits of highly pure monomers in order to control nucleophilic ring-opening polymerization NCAs. Hereby, monomer purity is investigated by relating melting points of NCAs with single-crystal and powder X-ray diffraction crystallography data, which further proves retained stereo-information of NCAs.