(S)-N-Fmoc-α-(4-Pentynyl)alanine is a non-natural, Fmoc-protected amino acid derivative. Its structure features a chiral alanine core with a 4-pentynyl side chain at the alpha position and an N-terminal 9-fluorenylmethoxycarbonyl (Fmoc) protecting group. The terminal alkyne moiety is a key functional handle. This compound is primarily used as a specialized building block in solid-phase peptide synthesis (SPPS), particularly for the incorporation of non-canonical amino acids into peptides. The alkyne group enables site-specific bioconjugation via copper-catalyzed azide-alkyne cycloaddition (CuAAC), a cornerstone click chemistry reaction. This makes it valuable for constructing peptide-drug conjugates, fluorescently labeled peptides, and other bioconjugates for research and drug discovery. It is also a key component in the synthesis of linkers for advanced modalities like antibody-drug conjugates (ADCs) and proteolysis-targeting chimeras (PROTACs), where precise attachment of payloads or E3 ligase ligands is required. The Fmoc group is standard for SPPS, allowing for orthogonal deprotection under mild basic conditions. The compound is typically handled as a high-purity solid for research use.