Cis-(3,4)-3,4-Diaminopyrrolidine-1-carboxylic acid tert-butyl ester is a chiral, heterocyclic building block featuring a pyrrolidine ring with two cis-configured amino groups at the 3 and 4 positions, protected by a tert-butyloxycarbonyl (Boc) group on the nitrogen. This compound is primarily utilized in medicinal chemistry as a key intermediate for the synthesis of bioactive molecules, including enzyme inhibitors, receptor modulators, and peptidomimetics. Its rigid cis-diamine scaffold is particularly valuable for constructing conformationally constrained analogs in drug discovery, especially in the development of central nervous system (CNS) agents and antiviral compounds. The Boc protection allows for selective deprotection under mild acidic conditions, facilitating further functionalization in multi-step synthetic routes.