Retatrutide

Retatrutide (Eli Lilly research code LY3437943, CAS 2381089-83-2) is a synthetic 39-residue peptide. The backbone contains α-aminoisobutyric acid (Aib) substitutions that resist DPP-4 cleavage at the N-terminus, and a central lysine carries a γGlu spacer linked to a C20 fatty diacid. The lipid linker binds non-covalently to circulating serum albumin, which is the source of retatrutide's long plasma half-life.

The published molecular formula and exact mass vary slightly across secondary sources; CertikLabs reports the deconvoluted average mass measured by LC-HRMS on each batch rather than relying on a secondary literature value.

Retatrutide is produced by Fmoc solid-phase peptide synthesis followed by selective side-chain conjugation of the C20 fatty-diacid linker to a single internal lysine. Two regions of the molecule generate most of the impurity burden:

• Long backbone (39-mer). Each coupling step has a finite efficiency; over 39 residues, accumulated deletion sequences and truncations are unavoidable and must be removed by preparative purification.
• Selective lipidation step. If the orthogonal protecting strategy fails, the C20-diacid linker can attach to the wrong lysine — these mis-acylated isomers are nearly co-eluting with the main peak and require LC-MS/MS peptide mapping to identify.

Additional analytes seen in real batches: Aib-position diastereomers, free unreacted C20-diacid, oxidized methionine / tryptophan, and high-molecular-weight aggregates. See common peptide impurities for the full taxonomy.

The standard CertikLabs panel for a retatrutide batch:

• RP-HPLC purity with wide-pore C4 column (TFA / MeCN, UV 214 nm)
• LC-HRMS identity (ESI-Q-TOF, deconvoluted average mass)
• Tryptic peptide mapping with LC-MS/MS to confirm full sequence and lipid attachment site
• Quantitative HPLC vs reference standard for content
• SEC-HPLC for aggregates

Each method, including column, mobile phase, gradient, and detection conditions, is reported on the Certificate of Analysis so the result is reproducible. See how to read a peptide COA for what each section should contain.

Co-activates GIP, GLP-1, and glucagon receptors. Discovery and early clinical pharmacology are described in Coskun et al. (2022) and the Jastreboff et al. Phase 2 obesity trial (NEJM 2023). CertikLabs reports only what is needed to verify the chemistry of a supplied sample.

Primary sources:

• Coskun T. et al., LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist.(PMID 35921818)
• Jastreboff A.M. et al., Triple-hormone-receptor agonist retatrutide for obesity — Phase 2 trial.(PMID 37356073)

CertikLabs does not publish dosing, administration routes, or clinical recommendations for retatrutide.

Like other lipidated incretin analogs, retatrutide is prone to surface adsorption, aggregation, and oxidation in solution. Lyophilized material is generally stable refrigerated and protected from light; once reconstituted, container choice, pH, and oxygen exposure all materially affect stability and any working solution should be re-verified analytically.