Methods, setup and safe handling for anhydrous hydrogen fluoride cleavage in Boc solid-phase peptide synthesis

Abstract

Solid-phase peptide synthesis (SPPS) using tert-butyloxycarbonyl (Boc)/benzyl (Bzl) chemistry is an indispensable technique in many laboratories around the globe, and it provides peptides to the pharmaceutical industry and to thousands of scientists working in basic research. The Boc/Bzl strategy has several advantages, including reliability in the synthesis of long and difficult polypeptides, alternative orthogonality regarding protecting groups and ease of producing C-terminal thioesters for native chemical ligation applications. In this process, anhydrous hydrogen fluoride (HF) is used to remove the side chain protecting groups of the assembled peptide and to release the peptide from the resin, a process typically described as 'HF cleavage'. This protocol describes the general methodology, apparatus setup and safe handling of HF, with the aim of providing comprehensive information on the safe use of this valuable, well-studied and validated cleavage technique. We explain the cleavage mechanism, the physicochemical properties and risks of HF, first aid measures and the correct use of the apparatus. In addition, we provide advice on scavenger selection, as well as a troubleshooting section and video material illustrating key steps of the procedure. The protocol comprises precleavage sample preparation (30 min-2.5 h), complete HF cleavage procedure (2 h) and reaction workup (30 min).

Bifluoride-catalysed sulfur(VI) fluoride exchange reaction for the synthesis of polysulfates and polysulfonates

“…Anhydrous HF and many onium halides are bulk chemicals, therefore practical industrial scale syntheses of bifluoride catalysts is expected. Demonstrating this, we carried out a 5-gram scale preparation of 1-ethyl-3-methylimidazolium bifluoride (EMI + [FHF] − ) (modified procedure based on refs 30,31). (Caution!…”

Leveraging the Knorr Pyrazole Synthesis for the Facile Generation of Thioester Surrogates for use in Native Chemical Ligation

“…[2,3] While the Boc-SPPS approach is highly efficient, Fmoc-SPPS has risen in popularity as it alleviates the need for dedicated HF cleavage apparatuses. [4] The alkyl-thioester linkages employed in Boc-SPPS have limited utility in Fmoc-SPPS as they are degraded during the repeated Fmoc deprotection steps. [5,6] Thus, multiple routes have been developed to introduce a C-terminal thioester into Fmoc-SPPS peptides.…”

HF‐Free Boc Synthesis of Peptide Thioesters for Ligation and Cyclization

“…Its synthesis has been described in detail 4a. It features a challenging sequence, rich in Arg and Cys.…”