Combination of Thiol‐Additive‐Free Native Chemical Ligation/Desulfurization and Intentional Replacement of Alanine with Cysteine

We report a novel strategy for native chemical ligation (NCL). Alanines not located at a ligation site are temporarily replaced with cysteines, and this enables efficient thiol‐additive‐free NCL, with subsequent desulfurization to regenerate the target peptide. We synthesized stresscopin‐related peptide and neuroendocrine regulatory peptide‐2 (NERP‐2) by this method. We confirmed that both conventional alkyl thioester and thioester‐equivalent N‐acyl‐N′‐methyl‐benzimidazolinone (MeNbz) can be adopted as thioester components for thiol‐additive‐free NCL of multi‐Cys‐containing peptides.