Omniligase-1: A Powerful Tool for Peptide Head-to-Tail Cyclization

Strategies for the efficient synthesis of peptide macrocycles have been a long-standing goal. In this paper, we demonstrate the use of the peptide ligase termed omniligase-1 as a versatile and broadly applicable enzymatic tool for peptide cyclization. Several head-to-tail (multi) cyclic peptides have been synthesized, including the cyclotide MCoTI-II. Cyclization and oxidative folding of the cyclotide MCoTI-II were efficiently performed in a one-pot reaction on a 1-gram scale. The native cyclotide was isolated and the correct disulfide bonding pattern was confirmed by NMR structure determination. Furthermore, compatibility of chemo-enzymatic peptide synthesis (CEPS) using omniligase-1 with methods such as chemical ligation of peptides onto scaffolds (CLIPS) was successfully demonstrated by synthesizing a kinase-inhibitor derived tricyclic peptide. Our studies indicate that the minimal ring size for omniligase-1 mediated cyclization is 11 amino acids, whereas the cyclization of peptides longer than 12 amino acids proceeds with remarkable efficiency. In addition, several macrocycles containing non-peptidicbackbones (e.g., polyethylene glycol), isopeptide bonds (amino acid sidechain attachment) as well as d-amino acids could be efficiently cyclized.