Chemical Synthesis of Proteins with Base‐Labile Posttranslational Modifications Enabled by a Boc‐SPPS Based General Strategy Towards Peptide C‐Terminal Salicylaldehyde Esters

Abstract

Chemical synthesis of proteins bearing base‐labile post‐translational modifications (PTMs) is a challenging task. For instance, O‐acetylation and S‐palmitoylation PTMs cannot survive Fmoc removal conditions during Fmoc‐solid phase peptide synthesis (SPPS). In this work, we developed a new Boc‐SPPS‐based strategy for the synthesis of peptide C‐terminal salicylaldehyde (SAL) esters, which are the key reaction partner in Ser/Thr ligation and Cys/Pen ligation. The strategy utilized the semicarbazone‐modified aminomethyl (AM) resin, which could support the Boc‐SPPS and release the peptide SAL ester upon treatment with TFA/H2O and pyruvic acid. The non‐oxidative aldehyde regeneration was fully compatible with all the canonical amino acids. Armed with this strategy, we finished the syntheses of the O‐acetylated protein histone H3(S10ac, T22ac) and the hydrophobic S‐palmitoylated peptide derived from caveolin‐1.

An adhesive peptide specifically induces microtubule condensation

“…30 The fluorescence intensity at 520 nm significantly increased with the increase of water content in the solvent (up to 90%), which was attributed to the AIE of the BP unit via strong hydrophobic interactions. 31,33 T2 was also assembled into the nanostructure as confirmed by fluorescence and UV-vis absorption spectra (Fig. S2, ESI†).…”

Oxidation and Phenolysis of Peptide/Protein C-Terminal Hydrazides Afford Salicylaldehyde Ester Surrogates for Chemical Protein Synthesis

“…Although unavoidable, the oxidized Met could be facilely reduced if necessary . In recent works, the reversibility of Met oxidation was exploited to assist peptide synthesis for various purposes. ,, It is worth mentioning that a sequence-dependent (vide infra) but noticeable side-product ( 9′ ) with a molecular weight 32 Da larger than that of 8 was also observed (Figure B-b). We speculated that one of the sulfurs of the C-terminal SAL­(−COOH) PDT was oxidized beside the one in Met1 (Figure S17), preventing the generation of aldehyde group.…”

“…However, it is somewhat cumbersome, as the “1” units have to be synthesized for individual ligation sites. For Boc-SPPS, ozonolysis-based strategy on aminomethyl (AM) resin has been developed but is incompatible with oxidation-sensitive amino acid residues such as Trp, Cys, and Met (Scheme d). , Recently, a new Boc-SPPS-based strategy has been developed, in which the semicarbazone-modified AM resin was used and the peptide SAL ester was generated upon treatment with TFA/H 2 O and pyruvic acid (Scheme e) . While these developments significantly advanced the synthetic utility of STL/CPL, more straightforward strategies are urgently needed, especially those viable for obtaining expressed protein SAL esters.…”

“…37,38 Recently, a new Boc-SPPS-based strategy has been developed, in which the semicarbazone-modified AM resin was used and the peptide SAL ester was generated upon treatment with TFA/H 2 O and pyruvic acid (Scheme 1e). 39 While these developments significantly advanced the synthetic utility of STL/CPL, more straightforward strategies are urgently needed, especially those viable for obtaining expressed protein SAL esters.…”

Synthesis of Disulfide Surrogate Peptides through a Serine/Threonine Ligation-Assisted Diaminodiacid Strategy

“…Then we noticed that a variety of non-NCL methods have been developed to perform peptide ligation at non-Cys sites, such as STL ligation and α-keto-acid-hydroxylamine (KAHA) ligation . And recently some important nonribosomal peptides and S-palmitoylated membrane proteins were successfully obtained through improved STL ligation . To this end, we envisage developing a novel approach combining DADA with STL ligation to perform disulfide bond replacement in CNP, with -Gly15-Ser16- selected as the ligation site.…”