Fmoc-O-tert-butyl-D-tyrosine is a protected derivative of the non-natural amino acid D-tyrosine. Its structure features an N-terminal 9-fluorenylmethoxycarbonyl (Fmoc) protecting group and a tert-butyl ether protecting group on the phenolic hydroxyl side chain of tyrosine. This dual protection renders the amino and phenolic hydroxyl groups inert during solid-phase peptide synthesis (SPPS) using the Fmoc strategy, while allowing for selective deprotection under mild acidic conditions. This compound is a crucial, high-purity building block specifically designed for the chemical synthesis of peptides and peptidomimetics. It is extensively used in pharmaceutical research and development to incorporate the D-tyrosine residue into peptide sequences, which can enhance metabolic stability, alter receptor binding affinity, or modulate the overall conformation and biological activity of the target peptide. The D-configuration is particularly valuable for creating peptides resistant to enzymatic degradation. Supplied as a white to off-white crystalline powder, it is a staple reagent in bioconjugation and the production of therapeutic peptides, peptide hormones, and diagnostic agents. Proper handling requires standard laboratory safety precautions for fine chemical powders.