Substrate-Directed Lewis-Acid Catalysis for Peptide Synthesis.

A Lewis-acid-catalyzed method for the substrate-directed formation of peptide bonds has been developed, and this powerful approach is utilized for the new "remote" activation of carboxyl groups under solvent-free conditions. The presented method has the following advantages: (1) the high-yielding peptide synthesis uses a tantalum catalyst for any amino acids; (2) the reaction proceeds without any racemization; (3) the new substrate-directed chemical ligation using the titanium catalyst is applicable to convergent peptide synthesis. These advantages overcome some of the unresolved problems in classical peptide synthesis.