N-(2,4-Dinitrophenyl)-L-leucine is a derivatized amino acid reagent primarily used in protein chemistry and analytical biochemistry. It plays a key role in the Sanger method for identifying N-terminal amino acids in peptides and proteins, where the 2,4-dinitrophenyl (DNP) group forms stable, chromophoric derivatives detectable by chromatography and UV spectroscopy. This compound also serves as a reference standard in amino acid analysis and supports research in enzymology, particularly for studying enzymes that process leucine or related substrates, as well as in the synthesis of labeled peptides for biochemical investigations.