Epimerization-Free Preparation of C‑Terminal Cys Peptide Acid by Fmoc SPPS Using Pseudoproline-Type Protecting Group

Preparation of C-terminal Cys-containing peptide acid by Fmoc solid-phase peptide synthesis (SPPS) is difficult due to base-mediated epimerization at Cys. In this paper, use of a C-terminal pseudoproline structure and Trt­(2-Cl) resin achieved epimerization-free direct preparation of the C-terminal Cys-containing peptide acid by Fmoc SPPS. Additionally, the C-terminal Cys­(ΨDmp,Hpro)-containing protected peptide segment was applied to an epimerization-free segment condensation reaction.