Retatrutide Molecular Weight, Sequence & CAS Reference

Introduction to Retatrutide Technical Specifications

Retatrutide (frequently designated as LY3437943 in early preclinical literature) represents a novel synthetic peptide engineered as a unimolecular triple agonist targeting three distinct metabolic receptors: the glucagon-like peptide-1 (GLP-1) receptor, the glucose-dependent insulinotropic polypeptide (GIP) receptor, and the glucagon receptor (GCGR). When evaluating this compound in preclinical research settings, establishing exact chemical parameters—including exact molecular weight, sequence fidelity, and salt counterion stoichiometry—is essential for reproducible experimental outcomes.

In analytical chemistry and structural biology assays, precise knowledge of a research compound's physical properties enables accurate stoichiometry during cell-culture exposure, ligand-binding assays, and surface plasmon resonance (SPR) protocols. Laboratories sourcing reagents across our all-peptides catalog require exact structural metrics to distinguish high-purity synthetic sequences from degraded or truncated side-products.

Primary Amino Acid Sequence and Structural Backbone

The primary sequence of retatrutide consists of a 39-amino-acid backbone derived from human GIP and GLP-1 sequences, modified heavily to incorporate non-canonical amino acids and site-specific fatty acid acylation. The published sequence for the free base structure is structured as follows:

H-Tyr-Aib-Glu-Gly-Thr-Phe-Thr-Ser-Asp-Val-Ser-Ser-Tyr-Leu-Glu-Gly-Gln-Ala-Ala-Lys(γGlu-C18 diacid)-Glu-Phe-Ile-Ala-Trp-Leu-Val-Lys-Gly-Arg-Gly-OH

Key structural features include the incorporation of alpha-aminobutyric acid (Aib) at position 2 to protect against cleavage by dipeptidyl peptidase-4 (DPP-4) endopeptidases in in vitro enzymatic assays. Furthermore, the lysine residue at position 20 is functionalized via a gamma-glutamic acid (γGlu) spacer attached to a C18 diacid (octadecanedioic acid) lipophilic side chain. This modification promotes non-covalent albumin binding in serum-containing research media, drastically altering the molecule's hydrodynamic radius and plasma clearance kinetics during rodent and non-human primate research.

Molecular Formula and Molecular Weight Metrics

The exact physical parameters of retatrutide depend on whether the compound is evaluated as an uncharged free base or as a lyophilized salt form containing bound counterions and residual hydration water. When calculating molarity for high-throughput screening or binding affinity studies, investigators must utilize the specific values dictated by the lot-specific analytical documentation.

The published theoretical metrics for retatrutide (free base) are defined as:

• Chemical Formula: C221H342N46O68 • Monoisotopic Mass: ~4728.52 Da • Average Molecular Weight: ~4731.33 g/mol

Because synthetic production requires solid-phase peptide synthesis (SPPS), the actual operational mass of a reconstituted vial reflects the peptide core plus counterions such as trifluoroacetate (TFA) or acetate. Failure to adjust for total salt content can introduce a 15% to 25% error margin when converting mass measurements (milligrams) into precise molar concentrations (micromolar) for microplate assays.

CAS Registry Numbers and Chemical Database Identifiers

Chemical abstracts assign unique numerical identifiers to distinct chemical entities, salts, and isomers. In academic literature and regulatory databases, retatrutide is cataloged under primary reference numbers that allow researchers to verify structural identity across chemical depositories.

• CAS Registry Number (Free Base): 2381089-83-2 • PubChem CID: 168199728 • IUPAC Name: Derived peptide structure with octadecanedioic acid extension at Lys20 • Internal Product Reference: GLP3-R Research Compound

Where specific salt forms (such as multi-trifluoroacetate salts) are generated during purification, distinct CAS numbers or sub-registry identifiers may be applied by chemical databases. Laboratories should always cross-reference CAS registry data with nuclear magnetic resonance (NMR) and liquid chromatography-mass spectrometry (LC-MS) data provided on the manufacturer's batch documentation.

Salt Counterion Impact: TFA vs. Acetate and Net Peptide Content

During modern reversed-phase high-performance liquid chromatography (RP-HPLC) purification, mobile phases frequently utilize trifluoroacetic acid (TFA) as an ion-pairing agent. Consequently, purified research peptides are isolated as TFA salts, where basic amino acid residues (Lys, Arg, N-terminus) form ionic complexes with trifluoroacetate anions.

Net Peptide Content (NPC) represents the actual percentage of peptide molecular weight relative to total lyophilized dry mass (which includes bound counterions and non-stoichiometric water). While total purity (chemical purity measured by HPLC) might exceed 98.0%, the Net Peptide Content typically ranges between 75% and 85%. For example, in a 10 mg vial of retatrutide TFA salt with an NPC of 80%, exactly 8.0 mg consists of the actual target peptide sequence, while 2.0 mg consists of counterions and trace residual moisture.

For quantitative in vitro pharmacology where precise receptor occupancy (EC50 / Ki) is evaluated, scientists must divide the weighed mass by the NPC fraction or consult our interactive reconstitution calculator to derive exact molar solution titers.

Comparative Specification Analysis: Multi-Agonist Class Profiles

To contextualize the physical parameters of retatrutide, it is useful to compare its molecular specifications against other synthetic incretin analogs utilized in metabolic research protocols. Distinct structural alterations dictate variable molecular weights, lipophilic side-chain profiles, and solubility behaviors across the class.

In multi-receptor binding studies, retatrutide is frequently bench-marked against dual and single agonist benchmarks. For example, tirzepatide features a 39-amino-acid backbone with a C20 fatty diacid acyl chain targeting GIP/GLP-1 receptors, exhibiting a molecular weight of ~4813.5 g/mol. Conversely, semaglutide consists of a shorter 31-amino-acid chain with a C18 diacid spacer, possessing a smaller molecular mass of ~4113.6 g/mol. In specialized metabolic co-formulation assays, investigators also compare these incretins alongside amylin analogs like cagrilintide to evaluate synergistic signal transduction pathways in cultured cell models.

Solubility, Lyophilization, and Reconstitution in Laboratory Environments

Retatrutide is supplied by PX1 Research as a sterile-filtered, lyophilized cake designed to maintain peptide stability during transportation and long-term storage. Due to the hydrophobic nature of the C18 diacid chain attached at Lys20, reconstitution behavior differs significantly from short, highly polar peptides.

Preclinical protocols suggest initial solubilization in sterile bacteriostatic water, phosphate-buffered saline (PBS, pH 7.4), or dilute aqueous buffer systems. Agitation should be restricted to gentle swirly inversion; vortexing must be strictly avoided as shear forces can induce peptide aggregation or denaturation of secondary hydrophobic alpha-helices. For deep structural assays requiring sub-nanomolar concentration gradients, serial dilutions should be conducted in polypropylene containers pre-treated or supplemented with low-binding surfactants (such as 0.01% BSA or Tween-20) to eliminate non-specific adsorption to vessel walls.

Quality Control: HPLC, Mass Spectrometry, and Endotoxin Standards

To ensure high experimental fidelity, PX1 Research subjects every lot of research peptides to rigorous analytical verification. Laboratory managers can independently inspect these metrics by reviewing our public Certificate of Analysis library.

Analytical standards enforced at our ISO 17025-accredited test facilities include:

1. High-Performance Liquid Chromatography (RP-HPLC): Confirms chemical purity ≥98.0%, identifying and quantifying potential deletion sequences or oxidation products. 2. Electrospray Ionization Mass Spectrometry (ESI-MS): Verifies exact mass matching the theoretical molecular weight (~4731.33 g/mol). 3. Bacterial Endotoxin Testing (LAL Assay): Guarantees endotoxin levels remain strictly below <0.01 EU/mg, preventing unwanted immune activation or cytokine interference in delicate cellular and tissue culture models.

For institutional procurement requiring specialized bulk parameters or customized salt exchange protocols (e.g., conversion from TFA to acetate salt), research facilities can establish dedicated accounts via our wholesale portal.

Handling and Storage Guidelines for In Vitro Assay Consistency

Lyophilized retatrutide standard cakes should be stored at -20°C or -80°C in a manual defrost freezer protected from light exposure. Under these conditions, the desiccated peptide core remains stable for up to 24 months without significant peptide bond hydrolysis or side-chain oxidation.

Following reconstitution into aqueous buffers, working aliquots should be used immediately or frozen in single-use portions at -80°C to eliminate repeated freeze-thaw cycles. Repeated thermal cycling accelerates side-chain degradation at sensitive glutamic acid and tyrosine residues. All manipulation of research compounds must be conducted within biological safety cabinets using aseptic techniques under strictly monitored research protocols.