Used in peptide synthesis as a protected amino acid derivative, particularly in the preparation of complex peptides where stereochemical control is critical. The tert-butyl ester (OtBu) group acts as a protecting group for the carboxylic acid, preventing unwanted reactions during coupling steps. The D-phenylglycine (D-Phg) moiety is often incorporated into pharmaceuticals and bioactive peptides due to its metabolic stability and conformational rigidity. Commonly employed in solid-phase and solution-phase synthesis of antibiotics, enzyme inhibitors, and receptor ligands. Its protected form allows for selective deprotection and further functionalization in multi-step synthetic routes.