This compound, 2-[2-(Fmoc-amino)ethoxy]ethylamine hydrochloride, serves as a key building block in solid-phase peptide synthesis (SPPS) and bioconjugation. It contains a free primary amine (as the hydrochloride salt) and an Fmoc-protected amine linked by an ethylene glycol spacer, providing a hydrophilic PEG-like unit. The Fmoc (fluorenylmethyloxycarbonyl) group acts as an orthogonal protecting group for the amine, allowing selective deprotection with base while the primary amine can be coupled to resins or carboxylic acids. This enables the stepwise incorporation of flexible spacers into peptides, improving solubility and bioactivity. It is essential in pharmaceutical research, drug discovery, and protein engineering for synthesizing modified peptides, conjugates, and targeted therapeutics.