NCarboxyanhydriten

N-Carboxyanhydrides, often abbreviated as NCAs, are cyclic derivatives of amino acids. They are five-membered rings containing an anhydride functional group and an imide nitrogen. The general structure features a carbonyl group adjacent to an oxygen atom within the ring, and another carbonyl group directly attached to the nitrogen atom. This unique structure makes NCAs highly reactive, particularly towards nucleophiles.

The primary utility of N-Carboxyanhydrides lies in their role as monomers for the synthesis of polypeptides and other related polymers through a process known as ring-opening polymerization. This polymerization typically proceeds without the need for activating agents or catalysts, and can occur under mild conditions. The reaction involves the nucleophilic attack on one of the carbonyl carbons of the NCA ring, leading to ring opening and the formation of a peptide bond. The released carbon dioxide is a byproduct of the polymerization.

NCAs can be prepared from amino acids by reacting them with phosgene or its safer alternatives, such as triphosgene. The stability of NCAs can vary depending on the amino acid side chain, with some being more prone to decomposition than others. Despite their reactivity, NCAs are valuable reagents in organic synthesis, particularly for creating well-defined peptide structures and functionalized polymers.