36 - Anionic Ring-opening Polymerization: N-Carboxyanhydrides

Abstract

Since their discovery by Leuchs in the year 1906,1 α-amino acid N-carboxyanhydrides (α-NCAs) have found increasing interest as monomers for the synthesis of oligopeptides and polypeptides. All N-carboxyanhydrides (NCAs) have the basic disadvantage that they are not stable on storage. The mechanisms of the spontaneous polymerization have not yet been elucidated. A detailed discussion of this aspect is presented in a recent monograph.2 Despite their instability, α-NCAs are highly useful for a variety of preparative purposes. Syntheses of various different low molecular weight amino acid derivatives such as N-ω-protected α,ω-diamino acids, amino acid alkyl esters, amino acid amides, amino acid hydroxamic acids, amino acid hydrazides, α-aminoacetophenones, hydantoic acids and α-isocyanatocarboxylic acid chlorides, have been described.2 In addition to pure oligopeptides, and polypeptides, a broad variety of block and graft copolymers have also been synthesized containing peptide chains attached to blocks or backbones derived from numerous different monomers. For instance two- or three- block copolymers have been prepared from poly(ethylene oxide) bearing one or two functionalized end groups.3–6 Three-block copolymers consisting of a central block of polystyrene and two flanks of peptide chains, or of central peptide blocks with flanks of polystyrene, have been reported.7–11 Similar block copolymers have been described based on blocks of anionically initiated poly(butadiene).9, 12–15 These block copolymers have been studied as models of proteins with hydrophobic or hydrophilic domains, and their compatibility with blood has been investigated.