Tirzepatide

Tirzepatide is a synthetic 39-residue peptide of molecular formula C₂₂₅H₃₄₈N₄₈O₆₈, with an average molecular mass of 4813.53 Da and a monoisotopic mass of 4810.5249 Da. The sequence opens Tyr-Aib-Glu-Gly-Thr-Phe-Thr-Ser-Asp-Tyr and closes Gly-Ala-Pro-Pro-Pro-Ser as a C-terminal amide. Alpha-aminoisobutyric acid, a non-proteinogenic alpha,alpha-disubstituted residue, occupies positions 2 and 13; every other position is proteinogenic.

The epsilon-amine of Lys20 carries a branched acyl assembly consisting of an eicosanedioic (C20 alpha,omega-dicarboxylic) acyl group linked through a gamma-glutamate spacer and two consecutive 2-[2-(2-aminoethoxy)ethoxy]acetyl (AEEA) units. That assembly contributes C₃₇H₆₅N₃O₁₂ to the intact composition, the unmodified backbone accounting for the remainder. Assembling the formula from the sequence and the four amide bonds of the acyl-spacer chain reproduces the deposited formula atom for atom, which provides an internal check on both the sequence assignment and the substitution site.

The molecule belongs to the incretin-family peptide analogues of the glucagon/secretin peptide superfamily. Two receptor entries are named against it: the gastric inhibitory polypeptide receptor (UniProt P48546) and the glucagon-like peptide 1 receptor (UniProt P43220). It is described in ChEMBL as a dual GIP and GLP-1 receptor agonist peptide.

Structurally the compound is separated from retatrutide by the position and composition of its lipid substituent, Lys20 with two AEEA spacer units against Lys17 with one, and by position 13, which is alpha-aminoisobutyric acid here and alpha-methyl-leucine in retatrutide. It is separated from the native 42-residue gastric inhibitory polypeptide by length, by the two Aib substitutions, by the C-terminal amide and by the presence of the acyl chain, none of which occur in the native sequence. The 82.11 Da average-mass gap to retatrutide and the far larger gap to unmodified incretin sequences make identity assignment by mass spectrometry straightforward.

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