(S)-1-(tert-Butoxycarbonyl)-2-(prop-2-yn-1-yl)pyrrolidine-2-carboxylic acid is a chiral pyrrolidine derivative featuring both a Boc-protected amine and a terminal alkyne functional group. This specific structural motif makes it a valuable building block in medicinal chemistry and chemical biology. Its primary application is as a key intermediate in the synthesis of targeted protein degraders, such as Proteolysis Targeting Chimeras (PROTACs) and related molecules. The carboxylic acid allows for amide coupling to a target protein ligand, while the terminal alkyne provides a handle for copper-catalyzed azide-alkyne cycloaddition (CuAAC) to attach an E3 ligase-recruiting moiety via a suitable linker. This dual functionality positions it as a versatile "linker-core" component in the modular assembly of degraders. The compound is commercially available from suppliers specializing in advanced pharmaceutical intermediates and chemical biology tools. Its use is documented in research focused on developing novel therapeutic strategies for diseases like cancer, where targeted protein degradation offers a promising modality beyond traditional inhibition.