Fragment 176-191 is a synthetic 16-amino acid peptide with the sequence Phe-Leu-Arg-Ile-Val-Gln-Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly-Phe, corresponding to residues 176–191 of its parent sequence. It has the molecular formula C₇₈H₁₂₃N₂₃O₂₂S₂, a molecular weight of 1,799.1 g/mol, and CAS number 66004-57-7, and carries an intramolecular disulfide bond between the cysteine residues at positions 182 and 189. It is closely related to but distinct from AOD9604, which carries an N-terminal tyrosine in place of phenylalanine; because tyrosine differs from phenylalanine by a single hydroxyl group, the two 16-mers differ by one oxygen atom — 1,799.1 versus 1,815.1 g/mol. Supplied as a white to off-white lyophilized powder; keep refrigerated at 36‑46 °F (2‑8 °C).