Native chemical ligation with Nalpha acyl transfer auxiliaries

Native chemical ligation (NCL) is a simple procedure that enables synthetic access to many proteins and is increasingly harnessed to study protein structure and function. However, the generality of this method is limited by the requirement for cysteine residues suitably positioned throughout the target protein. Auxiliary approaches have been developed to overcome this limitation, wherein a removable group is introduced at the amino terminus of a peptide conveying ligation properties comparable to cysteine. Present auxiliary approaches combine the thioester exchange concept applied first in NCL with a number of acyl transfer reactions first systematically explored by Kemp and coworkers. The current methods for auxiliary mediated ligation appear promising for the synthesis of proteins and in particular post-translational modified proteins.