Highly efficient and fast pre-activation cyclization of the long peptide: Succinimidyl ester-amine reaction revisited.

A new method for the pre-activation cyclization of a long peptide is described. The approach involves the formation of a pre-activated succinimidyl ester species in advance of amidation, which completely eliminates the potentially troublesome amine end-capping side reaction. The cyclization reactions proceed with high efficiency and fast reaction kinetics for the long peptide with 25 residues. The exploration and large-scale preparation of synthetic cyclic peptides should become more accessible and feasible with this approach. This method has a potential to be further applied for the synthesis of much longer and more complex cyclic peptides.