Efficient synthesis of cysteine-rich cyclic peptides through intramolecular native chemical ligation of N-Hnb-Cys peptide crypto-thioesters.

We herein introduce a straightforward synthetic route to cysteine-containing cyclic peptides based on the intramolecular native chemical ligation of in situ generated thioesters. Key precursors are N-Hnb-Cys crypto-thioesters, easily synthesized by Fmoc-based SPPS. The strategy is applied to a representative range of naturally occurring cyclic disulfide-rich peptide sequences.

Native Chemical Ligation Strategy to Overcome Side Reactions during Fmoc-Based Synthesis of C-Terminal Cysteine-Containing Peptides.

The Fmoc-based solid phase synthesis of C-terminal cysteine-containing peptides is problematic, due to side reactions provoked by the pronounced acidity of the Cα proton of cysteine esters. We herein describe a general strategy consisting of the postsynthetic introduction of the C-terminal Cys through a key chemoselective native chemical ligation reaction with N-Hnb-Cys peptide crypto-thioesters. This method was successfully applied to the demanding peptide sequences of two natural products of biological interest, giving remarkably high overall yields compared to that of a state of the art strategy.

A straightforward method for automated Fmoc-based synthesis of bio-inspired peptide crypto-thioesters.

Despite recent advances, the direct Fmoc-based solid phase synthesis of peptide α-thioesters for the convergent synthesis of proteins native chemical ligation (NCL) remains a challenge in the field. We herein report a simple and general methodology, enabling access to peptide thioester surrogates. A novel C-terminal -(2-hydroxybenzyl)cysteine thioesterification device based on an amide-to-thioester rearrangement was developed, and the resulting peptide crypto-thioesters can be directly used in NCL reactions with fast → shift kinetics at neutral pH.