4-Methyl-2-[[3-phenyl-2-(phenylmethoxycarbonylamino)propanoyl]amino]pentanoic acid, commonly known as Cbz-Phe-Leu-OH, is a protected dipeptide derivative. It consists of phenylalanine (Phe) and leucine (Leu) amino acid residues, where the N-terminus is protected by a carboxybenzyl (Cbz) group and the C-terminus is a free carboxylic acid. This compound is a white to off-white crystalline powder with a molecular formula of C23H28N2O5. This dipeptide is a fundamental building block in solid-phase peptide synthesis (SPPS) and solution-phase peptide chemistry. The Cbz protecting group is stable under acidic conditions but can be selectively removed via catalytic hydrogenation or hydrogenolysis, allowing for the sequential elongation of peptide chains. It serves as a key intermediate in the research and development of various bioactive peptides, including enzyme inhibitors, hormone analogs, and potential therapeutic agents. As a standardized and high-purity chemical, it is widely used in academic and industrial laboratories for constructing peptide libraries and studying structure-activity relationships. Proper handling requires standard laboratory precautions due to its potential as a respiratory and skin irritant.