Thalidomide-O-amido-C3-COOH is a specialty chemical intermediate primarily used as a building block in proteolysis-targeting chimeras (PROTACs). It acts as a ligand for the Cereblon (CRBN) E3 ubiquitin ligase, with a C3 carboxylic acid linker arm enabling conjugation to target protein binders. This facilitates ubiquitin-mediated degradation of disease-associated proteins, with applications in oncology, immunology, and neurodegenerative disorders. It supports the design of precise therapeutics that enhance efficacy and minimize off-target effects.