Fmoc-AA-OH, specifically (S)-2-((S)-2-((((9H-Fluoren-9-yl)methoxy)carbonyl)amino)propanamido)propanoic acid, is a protected dipeptide derivative. It consists of two alanine residues linked by an amide bond, with the N-terminal amino group protected by a 9-fluorenylmethoxycarbonyl (Fmoc) group. This structure is a fundamental building block in solid-phase peptide synthesis (SPPS). This compound is a critical reagent in the field of peptide chemistry and life sciences. It serves as a key intermediate for the automated, stepwise synthesis of peptides using the Fmoc strategy. The Fmoc protecting group is base-labile and can be cleanly removed under mild conditions, allowing for the sequential addition of amino acids to construct longer peptide chains. Its primary application is in the research and development of therapeutic peptides, peptide hormones, and biochemical probes. As a high-purity, commercially available Fmoc-protected dipeptide, it is essential for producing peptides with specific sequences for pharmaceutical, diagnostic, and biological studies. Handling requires standard precautions for laboratory chemicals, and it should be stored under inert conditions to maintain stability.