Re‐examination of the Reactivity of N‐Carboxy Amino Acid Anhydrides 1. Polymerisation of Amino Acid NCAs in Acetonitrile and in the Solid State in Hexane

Abstract

AbstractRing‐opening polymerisation of N‐carboxy anhydrides of γ‐benzyl‐L‐ glutamate, L‐alanine and L‐leucine by a primary amine initiator in acetonitrile and in hexane was examined, with care taken to avoid contamination by moisture. The polymerisation of amino acid NCAs initiated by butylamine in hexane proceeded in the crystalline state (solid state) because the NCA crystals did not dissolve in hexane. Although amino acid NCAs were believed to polymerise completely in acetonitrile, polymerisation of the amino acid NCAs in acetonitrile was found to stop at around 20% conversion. As resulting polypeptides did not dissolve in acetonitrile, the polymer terminals were considered to be occluded in the polymer precipitate. On the other hand, each amino acid NCA was much more reactive in the solid state in hexane than in acetonitrile. Especially, L‐leucine NCA showed remarkable reactivity in the solid state. The reactivity in the solid state was explained with reference to the crystal structure.