Phthalyl-DL-glutamic acid is primarily used in the pharmaceutical industry as an intermediate in the synthesis of various drugs. It plays a crucial role in the production of certain antibiotics and other therapeutic agents, where it acts as a protecting group for amino acids during peptide synthesis. This helps in controlling the reactivity of specific functional groups, ensuring the correct assembly of complex molecules. Additionally, it finds application in research and development for creating novel compounds with potential medicinal properties. Its stability and reactivity make it a valuable component in the design and manufacture of active pharmaceutical ingredients (APIs).