Fmoc-S-3-aminoisobutyric acid is a non-proteinogenic amino acid derivative widely used in solid-phase peptide synthesis (SPPS). Its structure features a 3-aminoisobutyric acid (Aib) backbone, a non-natural amino acid known for inducing helical conformations in peptides, protected at the N-terminus by a fluorenylmethyloxycarbonyl (Fmoc) group. This Fmoc protection is standard for modern SPPS methodologies. The primary application of this compound is as a specialized building block in peptide chemistry and medicinal research. Incorporation of Aib residues into peptide sequences enhances metabolic stability by resisting enzymatic degradation and can promote or stabilize specific secondary structures, such as α-helices or 3₁₀-helices. This makes it valuable for developing peptide-based therapeutics, peptidomimetics, and tools for studying protein-protein interactions. As a commercially available Fmoc-protected amino acid, it is a fundamental reagent for researchers constructing custom peptides with modified properties. It is handled under standard conditions for peptide synthesis reagents, requiring storage in a cool, dry place.