Cbz-Asp(OtBu)-Phe-Glu(OtBu)-OH is a protected tripeptide used in peptide synthesis. The Cbz (Carbobenzyloxy) group protects the N-terminus of the aspartic acid (Asp) residue, preventing it from reacting during synthesis. Both the aspartic acid and glutamic acid (Glu) residues have their side chain carboxyl groups protected by OtBu (tert-butyl) groups, ensuring these groups remain unreactive until selective deprotection is required. Phe (Phenylalanine) is the central amino acid in the sequence, contributing aromatic character. The -OH at the C-terminus indicates a free carboxyl group, allowing for further peptide coupling. This compound is used to introduce aspartic acid, phenylalanine, and glutamic acid into peptides with specific protections to control the reactivity and maintain the integrity of functional groups during synthesis.