(2S)-2-N-Fmoc-amino-2-methyl-9-decenoic acid is a non-proteinogenic, unnatural amino acid derivative. Its structure features an Fmoc (9-fluorenylmethoxycarbonyl) protecting group on the α-amino group, a methyl substituent at the α-carbon, and a terminal alkene (decenyl) side chain. This specific combination of protecting group and side chain functionality makes it a specialized building block. This compound is primarily used in solid-phase peptide synthesis (SPPS) as a protected amino acid precursor. The Fmoc group is a standard, base-labile protecting group for amine functionalities in Fmoc-based SPPS strategies. The α-methyl group introduces steric hindrance and conformational constraints, which can be utilized to modulate the peptide's secondary structure, stability against enzymatic degradation, and biological activity. The terminal alkene in the side chain provides a versatile chemical handle for further post-synthetic modifications via reactions such as thiol-ene click chemistry, enabling the site-specific attachment of labels, tags, or other functional groups to the peptide. As a research chemical, it is employed in the synthesis of peptidomimetics and structurally modified peptides for drug discovery and biochemical studies. Its use allows medicinal chemists to explore structure-activity relationships (SAR) and develop peptides with enhanced pharmacological properties.