Preparation and Application of an Inexpensive α-Formylglycine Building Block Compatible with Fmoc Solid-Phase Peptide Synthesis

α-Formylglycine (fGly) is a rare residue located in the active site of sulfatases, and serves as a precursor to pharmaceu-tically-relevant motifs. The installation of fGly motifs into peptides is currently challenging due to degradation under the acidic and nucleophile-rich conditions accompanying resin cleavage during solid-phase peptide synthesis. We report the synthesis of acid and nucleophile tolerant α-formylglycine building blocks from vitamin C, and use them to prepare Callyaerin A, a macrocyclic peptide containing an fGly-derived motif.