Zn-Catalyzed Nicotinate-Directed Transamidations in Peptide Synthesis

A chemoselective and catalytic transamidation for peptide synthesis is described. Transamidation under Zn catalysis is chemoselectively achieved by amino acid amide/peptidic amide derivatization with a tert-butyl nicotinate (tBu-nic) directing group. The directing group could be easily introduced on protected amino acid amides via Pd-catalyzed amidation with tert-butyl 2-chloronicotinate (tBu-nicCl). Under standard peptide coupling/deprotection conditions, the tBu-nic-equipped amino acid amides proved to be fully inert, allowing them to be easily built-in in complex molecules. The disclosed method was evaluated in the synthesis of diverse dipeptides, in dipeptide segment coupling, in side-chain modification of a solid-supported tetra-/pentapeptide, and in the macrocyclization of a heptapeptide.