Retatrutide Research Guide

Retatrutide is a modified peptide studied as an agonist of GLP-1, GIP, and glucagon receptors; evaluating a laboratory lot requires separate evidence of identity, purity, and content.

At a glance

• Its three receptor targets are GLP-1R, GIPR, and GCGR.
• Sequence substitutions and a fatty diacid attachment serve different molecular functions.
• Published receptor experiments characterize the studied molecule; they do not certify another supplier's lot.

What defines the molecule

Also identified as LY3437943, retatrutide has a 39-residue backbone engineered from GIP. The noncanonical residue α-aminoisobutyric acid (Aib) at position 2 provides resistance to DPP-4 cleavage. Aib at position 20 and α-methyl-L-leucine at position 13 contribute to its receptor activity profile. A C20 fatty diacid is attached through a linker at lysine 17, enabling albumin binding. These features are described in Coskun and colleagues' molecular characterization.

Read receptor results in context

Binding affinity

How strongly a ligand interacts with a receptor under defined conditions, typically described using K_d or K_i.

Functional potency

The concentration producing a specified response. An EC₅₀ in a cAMP assay describes half the measured maximal response, rather than binding strength.

Maximum response

The response achievable in that assay. It must be considered alongside potency.

Record the receptor species, cell model, receptor expression, endpoint, incubation time, and albumin conditions when comparing experiments. Albumin can bind acylated peptides and alter the free concentration available to receptors. A lower EC₅₀ from a different assay does not establish universally stronger activity.

Check the material before an experiment

• Match the vial's lot identifier to the report and confirm the specified sequence, modifications, and salt form.
• Check the HPLC method, detection wavelength, chromatogram, and integration basis.
• Review the LC-MS charge assignment and expected mass; an intact mass match supports identity but cannot establish every structural detail.
• Identify any quantitative content measurement, residual-water result, and documented storage or retest conditions.

HPLC area percentage is not the peptide mass fraction of the powder. Counterions and residual water can contribute to its weight, as explained in Bachem's analytical FAQ. Use the COA interpretation guide to assess those measurements and the receptor mechanisms overview to compare assay types.

All laboratory reference guides

Retatrutide molecular reference specifications

Retatrutide is also identified as LY3437943. WHO Proposed INN List 128 provides a structural description of a modified 39-residue peptide, including noncanonical residues, terminal amidation and an acylated lysine. The parent formula and mass exclude counterions, residual water and any formulation excipients. They describe the molecule used for reference comparisons, not a measured result for a supplied lot.

A plain one-letter backbone is incomplete unless its modifications are also specified. Aib at positions 2 and 20, 2-methyl-L-leucine at position 13, the lysine-17 side-chain attachment and the C-terminal amide belong to the molecular definition. Use the complete published structure when assessing identity.

Retatrutide molecular reference specifications specifications

Compound / development code	Retatrutide / LY3437943
Parent CAS registry number	2381089-83-2
Parent molecular formula	C221H342N46O68
Parent molecular weight	Approximately 4731 g/mol; calculated from the parent molecular formula
Backbone and modifications	39 residues; Aib2 and Aib20; 2-methyl-L-Leu13; acylated Lys17; C-terminal Ser-NH2; full structure in WHO INN List 128
Supplied chemical form	Verify the current product specification; not established by the parent formula

Separate receptor evidence from lot evidence

Published receptor characterization provides a framework for interpreting binding and functional experiments. It does not independently establish that a purchased sample has the specified sequence, side-chain attachment or quantitative content. Assess structural identity and sample quality separately before comparing an experimental response with the literature.

An assay comparison should preserve the receptor species, cell system, endpoint, reference agonist and albumin conditions. Binding affinity and functional potency are different measurements; a functional EC50 also depends on how the response was produced and analyzed. Do not rank results from unlike assay systems as though they were one universal potency scale.

Connect each format to its own records

Vials and raw research powder share the molecular reference, but packaging, formulation and lot evidence remain specific to the selected product. A nominal amount is distinct from measured peptide content. Keep the analytical basis clear when a report describes peptide mass, salt mass or total as-received material.

For the current lot, match the product size and formulation to its report identifier. Review identity data, the purity method and quantitative content as separate findings. A high main-peak percentage cannot establish every structural feature or account for all water, counterions and excipients. Use actual CMS publication and modification dates for this guide; the editorial review date is a separate record.

Primary sources and chemical records

• WHO Proposed INN List 128: retatrutide structural description, page 1051
• GSRS retatrutide identity record, UNII NOP2Y096GV
• Coskun et al.: molecular and receptor characterization of LY3437943 (2022)
• USP researchers: reference standards and quality characterization of synthetic peptides (2023)

Prepared by BulkGLP. Editorial review: 2026-11-04.