This compound is an Fmoc-protected (S)-aspartic acid derivative, specifically Fmoc-Asp[O-(4-(Dde-amino)benzyl)]-OH, where Dde denotes the 1-(4,4-dimethyl-2,6-dioxocyclohexylidene)-3-methylbutyl protecting group. It is utilized in solid-phase peptide synthesis (SPPS) to introduce an aspartic acid residue with an orthogonally protected aniline handle on the side-chain ester. The Fmoc group protects the α-amino functionality, enabling standard chain elongation. The Dde group on the para-aminobenzyl ester can be selectively cleaved with mild hydrazine (e.g., 2% in DMF), exposing the aniline for conjugation to drugs, fluorophores, sugars, or other moieties. This makes it invaluable for synthesizing peptide conjugates, antibody-drug conjugates (ADCs), glycopeptides, and bioactive molecules in pharmaceutical and biotechnological research, offering high selectivity, purity, and compatibility with Fmoc protocols.