Used in solid-phase peptide synthesis, particularly for constructing complex peptides with controlled stereochemistry. The Fmoc group provides temporary N-terminal protection that is easily removed under mild basic conditions, allowing stepwise assembly. The tert-butyl (Otbu) side chain protection prevents unwanted side reactions during coupling, especially important for aspartic acid residues prone to β-carboxyl activation. Being the D-isomer, it is incorporated to enhance peptide stability against enzymatic degradation, commonly used in therapeutic peptides, peptidomimetics, and research tools studying protein folding and enzyme activity. Its use supports the synthesis of peptides with improved pharmacokinetic properties and resistance to proteolysis.