(S)-2-Amino-6-(tert-butoxy)-6-oxohexanoic acid, also known as L-2-Aminohexanedioic acid 6-tert-butyl ester or Boc-L-Glu(OtBu)-OH, is a protected derivative of the natural amino acid L-glutamic acid. It features both the α-amino group protected by a tert-butoxycarbonyl (Boc) group and the γ-carboxylic acid side chain protected by a tert-butyl (OtBu) ester. This white to off-white crystalline powder is a crucial building block in peptide synthesis, particularly in solid-phase peptide synthesis (SPPS) using the Boc strategy. As a key chiral intermediate, it is extensively used in the pharmaceutical industry for the synthesis of complex peptides and peptidomimetics. Its primary role is to incorporate a glutamic acid residue into a peptide chain while preventing unwanted side reactions at the reactive amino and carboxyl groups during the coupling steps. This compound is fundamental in research and development of therapeutic peptides, including hormone analogs, enzyme inhibitors, and other bioactive molecules. The dual protection (Boc and OtBu) makes it orthogonal to other protecting groups like Fmoc, allowing for flexibility in synthetic strategies. It is characterized by high chemical purity and enantiomeric excess, which are critical for producing peptides with defined biological activity. Proper handling requires standard laboratory precautions for fine chemicals.