High- Throughput Synthesis of Peptide a- Thioesters: A Safety Catch Linker Approach Enabling Parallel Hydrogen Fluoride Cleavage

Peptide -thioesters are fundamental building blocks in peptide and protein science, providing powerful tools for peptide medicinal chemistry. The application of peptide -thioesters in native chemical ligation reactions has enabled synthetic access to cysteine-rich peptides and proteins, cyclic peptides as well as labeled and chemically modified biomolecules. An efficient high-throughput synthesis of peptide -thioester building blocks would be beneficial for many medicinal chemical applications that require peptides and proteins. Herein we present a novel synthetic route to cysteine-rich peptide -thioesters using a safety catch linker that enables a parallel synthetic strategy for chemical protein synthesis. ACP(68-75), bradykinin and dynorphin(1-13) were synthesized via Boc chemistry in their thioester form on a safety catch amide linker (SCAL), employing polystyrene- or poly(ethylene glycol)-based resins, compartmentalized in tea bags. This compartmentalized resin/linker strategy facilitated a parallel hydrogen fluoride cleavage in which each peptide thioester was subsequently cyclized by native chemical ligation, demonstrating the utility of this approach. A naturally occurring bioactive cyclic peptide, the sunflower trypsin inhibitor SFTI-1, was synthesized to demonstrate the viability of this method to access important peptide biomolecules.