Copper(II)-mediated C-H sulphenylation or selenylation of tryptophan enabling macrocyclization of peptides

Advanced Insulin Synthesis by One-pot/Stepwise Disulfide Bond Formation Enabled by S-Protected Cysteine Sulfoxide

An advanced insulin synthesis is presented that utilizes one-pot/stepwise disulfide bond formation enabled by acid-activated S-protected cysteine sulfoxides in the presence of chloride anion. S-chlorocysteine generated from cysteine sulfoxides reacts with an S-protected cysteine to afford S-sulfenylsulfonium cation, which then furnishes the disulfide or reversely returns to the starting materials depending on the S-protection employed and the reaction conditions. Use of S-acetamidomethyl cysteine (Cys(Acm)) and its sulfoxide (Cys(Acm)(O)) selectively give the disulfide under weak acid conditions in the presence of MgCl2 even if S-p-methoxybenzyl cysteine (Cys(MBzl)) and its sulfoxide (Cys(MBzl)(O)) are also present. In contrast, the S-MBzl pair yields the disulfide under more acidic conditions in the presence of a chloride anion source. These reaction conditions allowed a one-pot insulin synthesis. Additionally, lipidated insulin was prepared by a one-pot disulfide-bonding/lipidation sequence.

Non-symmetric stapling of native peptides

Stapling has emerged as a powerful technique in peptide chemistry. It enables precise control over peptide conformation leading to enhanced properties such as improved stability and enhanced binding affinity. Although symmetric stapling methods have been extensively explored, the field of non-symmetric stapling of native peptides has received less attention, largely as a result of the formidable challenges it poses - in particular the complexities involved in achieving the high chemo-selectivity and site-selectivity required to simultaneously modify distinct proteinogenic residues. Over the past 5 years, there have been significant breakthroughs in addressing these challenges. In this Review, we describe the latest strategies for non-symmetric stapling of native peptides, elucidating the protocols, reaction mechanisms and underlying design principles. We also discuss current challenges and opportunities this field offers for future applications, such as ligand discovery and peptide-based therapeutics.