Z-Glu(OtBu)-OSu is a specialty chemical reagent used in solid-phase and solution-phase peptide synthesis. It serves as an activated, protected form of L-glutamic acid, where the α-amino group is protected with a benzyloxycarbonyl (Z) group, the side-chain γ-carboxyl is esterified with tert-butyl (OtBu) to prevent side reactions, and the α-carboxyl is activated as a succinimidyl ester (OSu) for efficient amide bond formation with free amino groups of other amino acids or peptides. This design ensures high selectivity, minimizing unwanted reactions and enabling the precise construction of complex peptide sequences. It is commonly employed in the production of pharmaceutical peptides, bioactive molecules, and research-grade compounds. The orthogonal nature of the protecting groups allows for stability during synthesis and straightforward deprotection under mild conditions, making it essential in organic synthesis and medicinal chemistry.