This compound, known as Fmoc-4-aminobutylamine hydrochloride, is a selectively protected diamine utilized in advanced peptide and oligonucleotide synthesis. The fluorenylmethyloxycarbonyl (Fmoc) group protects the primary amine at one end, while the other amine is available as a hydrochloride salt for coupling reactions. It functions as a versatile linker or spacer arm, facilitating the attachment of peptide chains to solid supports, surfaces, or other molecules in solid-phase synthesis protocols. Valued for the Fmoc group's stability in basic media and its orthogonal removal under mild acidic conditions (e.g., with piperidine), it enables stepwise assembly of complex bioconjugates, pharmaceuticals, and research probes with high efficiency and low side reactions. Applications include drug development, biochemical assays, and the creation of modified peptides for therapeutic and diagnostic purposes.