In summary, Fmoc-protected hThr building block 6 can be readily synthesized from vitamin C using inexpensive reagents and used in SPPS to install hThr residues into peptides. Utilization of hThr as a precursor to fGly can circumvent incompatibility issues associated with the intolerance of fGly towards the conditions/species encountered during SPPS, and the hThr residue can then be cleanly converted to fGly off-resin using NaIO4. We demonstrated that our approach can not only be used to prepare fGly-functionalized peptides but also used to prepare cyclic peptides bearing pharmaceutically important rigidifying motifs, and may therefore have broad applications in the fields of bioconjugation and pharmacology.