This compound, (R)-5-((9H-Fluoren-9-yl)methoxy)-4-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)-5-oxopentanoic acid, also known as Fmoc-Glu(Fmoc)-OH, is a doubly protected derivative of L-glutamic acid used in solid-phase peptide synthesis (SPPS). The two fluorenylmethoxycarbonyl (Fmoc) groups protect the α-amino group and the side-chain carboxylic acid, preventing unwanted side reactions during peptide bond formation. Fmoc groups are selectively removed under mild basic conditions (e.g., with piperidine), allowing stepwise peptide assembly. This reagent is crucial for incorporating glutamic acid residues into complex peptides and proteins for research, pharmaceutical, and biotechnology applications, valued for its stability and orthogonal deprotection.