This compound is an Fmoc-protected linker molecule, specifically 3-(2-((((9H-Fluoren-9-yl)methoxy)carbonyl)amino)ethoxy)propanoic acid, used in solid-phase peptide synthesis (SPPS) and bioconjugation applications. It consists of an Fmoc-protected primary amine linked through an ethyleneoxy spacer to a propanoic acid group. The carboxylic acid terminus enables facile coupling to resins, peptides, or other biomolecules, while the Fmoc group safeguards the amine during synthesis and can be selectively removed with piperidine under mild basic conditions. This structure imparts hydrophilicity and flexibility, making it ideal for enhancing peptide solubility, creating PEG-like spacers in peptide-drug conjugates, and modifying proteins or oligonucleotides for improved pharmacokinetics and stability. Its orthogonality with common SPPS reagents ensures high efficiency in multistep assemblies.