4-Nitro-L-phenylalanine monohydrate is primarily used in biochemical research as a non-natural amino acid. It serves as a substrate or inhibitor in enzymatic studies, particularly for investigating enzyme specificity and mechanisms. Its nitro group makes it a useful probe in spectroscopic studies, allowing researchers to track and analyze protein interactions and structural changes. Additionally, it is employed in the synthesis of modified peptides and proteins to study their function and stability. This compound also finds application in the development of novel pharmaceuticals, where it aids in understanding drug-target interactions and optimizing therapeutic agents.