Use of Anhydrous Hydrogen Fluoride in Peptide Synthesis. II. Procedures for the Syntheses of Simple Peptides

Abstract

Detailed conditions for handling simple peptide-derivatives with anhydrous hydrogen fluoride (HF) were presented.Since HF has a strong affinity for peptides, the removal of excess HF from the reaction products is rather difficult, but is essential to obtain the product as good crystals. Syntheses of the following peptides were carried out successfully as examples of the HF procedure:The possibility of removing the S-benzyl group by acidolysis was the first indication of the usefulness of anhydrous hydrogen fluoride (HF) for peptide synthesis;1) this was confirmed by the formation of oxytocin from the fully-protected nonapeptide. The general properties of HF as a reagent for the removal of various protective groups have been discussed in our preceding papers.2,3) In this study, detailed conditions for the synthesis of simple peptides were investigated to demonstrate how the HF-procedure can be applied in general peptide synthesis. The HF reaction was carried out in the apparatuses described in the preceding papers.2,3)Although completely dry HF is desirable for accelerating the cleaving reaction, a further drying procedure was unnecessary for the synthesis of simple peptides when HF of more than 99% purity was used under mild conditions. Generally, the HF molecule has a strong affinity for peptides through the hydrogen bonds, and it takes a very long time to remove the excess HF from peptides, even in vacuo. The results shown in Fig. 1 demonstrate that 0.19, 1.57, and 1.81 equivalents of HF were still attached to acetyl-Lleucine, L-leucylglycine and L-leucylglycylglycine respectively, even when their HF-solution had been kept under a vacuum (2-3mmHg) for 20hr at room temperature.These results indicate that about 1.4 equivalents of HF are bound to an amino group and that about 0.2 equivalent of HF is attached to one peptide-bond under these conditions. Therefore, the difficulty in removing HF from peptides increases with the number of the peptide-bonds.Nevertheless, the complete removal

Synthesis and structural studies of N‐p‐toluensulfonyl cyclodipeptides

“…Accordingly the Tus-Phe CaH of I is not shielded, but resonates, as expected, at low exhibiting the same chemical shift shown by the corresponding a-proton of 11. The D-Phe C"H of I, on the other hand, is strongly shielded by the Tos-Phe aromatic ring and appears at 2.206, a value analogous to that found for D-RO C"H in 11. The values of the vicinal coupling constants are in accordance with these data, in particular, whereas the Tos-Phe residue exhibits two small and almost equal Jab coupling constants, one of the D-Phe Jab i s very large (10 Hz) and the other small (3.5 Hz).…”

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

“…The most effective and commonly used acid for this purpose is anhydrous HF (Box 2; refs. 11,12,14), although other acids such as hydrogen bromide 28,29 and trifluoromethanesulfonic acid in TFA have also been used successfully 30 .…”

“…Fmoc-SPPS is the technique that is most commonly used, possibly because of its overall safer handling methods, and it is also the strategy of choice for peptides that contain acid-sensitive modifications such as O-glycosidic or phosphate residues. Nevertheless, many laboratories continue to embrace the original side chain protecting strategy used by Merrifield 4 for SPPS, namely Boc/Bzl [11][12][13][14] . This strategy has several advantages, including reliability in the synthesis of long polypeptides, alternative orthogonality regarding protecting groups and ease of producing C-terminal thioesters for native chemical ligation (NCL) applications.…”

Chemical synthesis of proteins in solution

“…13 We therefore decided to adopt the maximum protection approach using the carbodiimide/additive procedure for the segment condensation reactions in solution. One is to assemble the molecule with Bzl-based protecting groups, and after obtaining the entire sequence, removing the protecting groups by acidolysis with a strong acid such as HF [15][16][17] or trifluoro-methane sulfonic acid (TFMSA). One is to assemble the molecule with Bzl-based protecting groups, and after obtaining the entire sequence, removing the protecting groups by acidolysis with a strong acid such as HF [15][16][17] or trifluoro-methane sulfonic acid (TFMSA).…”

“…19 Both chemistries have different features and different problems. [15][16][17] Thus, the strategy was to assemble the entire protein molecule by the condensation of fully protected segments in solution, applying the Boc/Bzlbased chemistry. [15][16][17] Thus, the strategy was to assemble the entire protein molecule by the condensation of fully protected segments in solution, applying the Boc/Bzlbased chemistry.…”