Polymerization mechanism of N-carboxy-α-amino acid anhydride by organometallic compounds. II.. Reaction with organozinc compounds

Reactions of N-carboxy-α-amino acid anhydride (NCA) with dialkylzinc or related organozinc compounds were studied to elucidate the polymerization mechanism of NCA by dialkylzinc as initiator. The first stage of initiation reaction is a hydrogen abstraction reaction of dialkylzinc from NH group of α-amino acid NCA resulting in the formation of an activated NCA. The second stage of initiation is a reaction between two molecules of the activated NCA forming a zinc carbamate group. Propagation reaction is a carbonyl addition of the zinc carbamate group to the activated NCA to form a mixed anhydride which changes into an amide group releasing carbon dioxide. Regeneration of the activated NCA is supposed to be done by the reaction of free α-amino acid NCA with the zinc atom bonded to nitrogen atom at the growing chain end.