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/H 2 O 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.