Used in peptide synthesis as a protected amino acid derivative, enabling selective coupling and minimizing side reactions. The Fmoc group allows for mild base deprotection, while the 2-phenylisopropyl ester protects the carboxylic acid side chain of aspartic acid, preventing unwanted cyclization or branching during solid-phase synthesis. This protection scheme is especially valuable in the preparation of complex peptides and proteins where precise control over reactivity is required. The bulky ester group also improves solubility in organic solvents commonly used in peptide coupling steps. After chain assembly, the ester can be removed under mild acidic conditions without affecting the peptide backbone or other protecting groups, making it compatible with Fmoc-based strategies.