Substrate-controlled amide bond formation: Innovation of peptide synthesis

Peptides, which are elongated of peptides chain of amino acids linked by amide bonds, are elementary components in living systems and regulate many biological processes. Since the solid- phase peptide synthesis was introduced by Merrifield in 1964, chemical synthesis of peptides using solid-phase system has emerged as a valuable method due to its ease of operation and rapid synthesis of desired peptides. However, despite of the effectiveness of the solid-phase approach, typical reaction requires excess amounts of coupling reagents, bases, and amino acids to achieve maximum conversion. And the ease of operation led to accumulate undesired segments together with target peptide because solid-phase system is generally carried out by coupling amino acids with N-terminal amino acid residue of peptides in a stepwise approach without any isolation and characterization at each step. To solve these issues, we focused on the development of catalytic liquid-phase synthesis, which has advantage of isolating the growing peptide chain from reaction solution after each coupling step. Although several liquid-phase methods have been developed, there is a still considerable room for the improvement of racemization, generality, and ligation reaction. In this view, we have developed a mild, practical, and efficient methods based on substrate-control by using boronic acid, niobium, and tantalum as catalysts. Our methods can be applied for a broad variety of amino acids to furnish the desired peptides in excellent yields without significant loss of stereochemical integrity. The developed straightforward approach overcome a lot of problem associated with peptide synthesis. This article describes our recent achievement based on catalytic substrate-controlled peptide synthesis. © 2021 Society of Synthetic Organic Chemistry. All rights reserved.