Phenylthiohydantoin-norleucine is primarily utilized in the field of protein sequencing and peptide analysis. It serves as a derivative in the Edman degradation process, a method used to determine the amino acid sequence of proteins. By forming stable phenylthiohydantoin derivatives, it aids in the step-by-step identification of amino acids from the N-terminus of a peptide or protein. This compound is particularly valuable in biochemical research and proteomics, where understanding protein structure and function is critical. Its application extends to quality control in peptide synthesis and the study of protein modifications, making it an essential tool in advancing molecular biology and biotechnology.