N- to C-Peptide Synthesis, Arguably the Future for Sustainable Production.

A revolution in peptide production arrived from the innovation of carboxylate to amine C- to N-direction solid-phase synthesis. This cornerstone of modern peptide science has enabled multiple academic and industrial applications; however, the process of C- to N-solid phase peptide synthesis (C-N-SPPS) has extreme process mass intensity and poor atom economy. Notably, C-N-SPPS relies upon the use of atom-intensive protecting groups, such as the fluorenylmethyloxycarbonyl (Fmoc) protection and wasteful excess of protected amino acids and coupling agents. On the other hand, peptide synthesis in the amine to carboxylate N- to C-direction offers potential to minimize protection and may arguably enable more efficient means for manufacturing peptides. For example, efficient amide bond formation in the N- to C-direction has been accomplished using methods employing thioesters, vinyl esters, and transamidation to achieve peptide synthesis with minimal epimerization. This review aims to provide an overview of N- to C-peptide synthesis indicating advantages in taking this avenue for sustainable peptide production.