O-(tert-Butyl)-N-[(9H-fluoren-9-ylmethoxy)carbonyl]-D-allo-threonine is a protected derivative of the non-proteinogenic amino acid D-allo-threonine. Its structure features two key protective groups: the amine is protected by the base-labile 9-fluorenylmethoxycarbonyl (Fmoc) group, and the side-chain hydroxyl group is protected by the acid-labile tert-butyl (t-Bu) ether group. This combination makes it a chiral, orthogonally protected building block. This compound is primarily used as a specialized amino acid derivative in solid-phase peptide synthesis (SPPS), particularly employing the Fmoc/t-Bu strategy. The D-allo configuration of threonine is of significant interest in medicinal chemistry and peptide research for constructing peptides with specific secondary structures, enhanced metabolic stability, or altered biological activity profiles compared to their L-amino acid counterparts. It serves as a crucial intermediate for synthesizing peptide-based drug candidates, bioactive probes, and peptidomimetics. The orthogonal protection scheme allows for sequential and selective deprotection during peptide chain assembly and subsequent modifications. Its high purity and defined chirality are essential for producing peptides with precise stereochemistry, which is critical for their intended biological function and interaction with target proteins.