Fig. 1
From: Accelerated microfluidic native chemical ligation at difficult amino acids toward cyclic peptides
Cyclic peptide synthesis using NCL and its implementation under microfluidic conditions. a Principle of NCL reaction applied to cyclic peptide synthesis. The NCL reaction involves the chemoselective reaction of a C-terminal peptide alkylthioester (e.g., MPA peptide thioester 1) or arylthioester (e.g., MPAA peptide thioester 2) with an N-terminal cysteinyl peptide. The intramolecular version of this reaction enables backbone cyclization. The ligation proceeds in the presence of an exogenous thiol catalyst (typically MPAA) and a reductant (typically TCEP). b Implementation of NCL under microfluidic conditions toward backbone peptide cyclization. The system is fed with a stable precursor, which is activated into a highly reactive thioester species before entering the ligation module. c Reactive SEAE peptide thioesters are generated from the stable SEA cyclic disulfide (SEAoff) 3 upon reduction with TCEP or from the reduced SEAon bisthiol 4. SEAE peptide thioesters 5 enable extremely fast NCL even with difficult C-terminal amino acids
