Used in solid-phase peptide synthesis as a protected amino acid building block, particularly for incorporating conformationally constrained leucine derivatives into peptide chains. The Fmoc group allows for mild base-labile protection, compatible with standard Fmoc-strategy protocols. The 4,5-dehydro modification introduces a double bond within the side chain, which can influence peptide backbone folding and side chain orientation, making it useful in studies of peptide structure-activity relationships, enzyme substrate design, and development of bioactive peptides with enhanced stability or selectivity. Commonly applied in research settings for synthesizing modified neuropeptides, enzyme inhibitors, and peptidomimetics.