S-protected derivative for the introduction of a deamino-penicillamine residue. Building block for the preparation of oxytocin and vasopressin antagonists. Peptide thioesters for chemical ligation may be obtained by Fmoc-SPPS using a deaminopenicillamine-derived linker, as premature cleavage during Fmoc removal is inhibited by steric hindrance. Tegge et al. developed a deaminopenicillamine-based disulfide linker for the Fmoc-SPPS of cyclic Cys-containing peptides.