Cis-1-Boc-4-hydroxy-D-proline methyl ester is a chiral, protected amino acid derivative. It features a cis-configuration of the hydroxy group at the 4-position of the proline ring, which is a D-enantiomer. The molecule is protected with a tert-butoxycarbonyl (Boc) group on the nitrogen and a methyl ester on the carboxylic acid, making it a versatile and stable building block for synthetic chemistry. This compound is primarily employed as a key chiral intermediate in the synthesis of complex pharmaceutical agents. Its rigid, functionalized proline scaffold is valuable for constructing peptidomimetics and active pharmaceutical ingredients (APIs), particularly those targeting the central nervous system or metabolic disorders. The presence of both protected amine and hydroxy groups allows for selective deprotection and further functionalization, enabling its incorporation into larger molecular frameworks. As a Boc-protected derivative, it offers advantages in solid-phase peptide synthesis (SPPS) and solution-phase strategies due to its orthogonal protection scheme. The specific cis-4-hydroxy-D-proline motif is a sought-after structural element for modulating the conformational and biological properties of final drug candidates.