Semaglutide is a long-acting glucagon-like peptide-1 receptor agonist supplied as a lyophilised research peptide for laboratory investigation of incretin receptor pharmacology. This guide covers the semaglutide research peptide in depth: its 31-residue structure and three engineered modifications, the receptor mechanism described in the literature, verified physicochemical data, concentration references for solution preparation, and what a meaningful certificate of analysis must show.
Key takeaways
- Semaglutide is a 31-residue analogue of GLP-1(7-37) with roughly 94% sequence homology to the native hormone.
- Three modifications define it: α-aminoisobutyric acid (Aib) at position 8, arginine in place of lysine at position 34, and a C18 fatty diacid attached to Lys26 through a γ-glutamic acid and two AEEA spacers.
- Verified identity data: CAS 910463-68-2, molecular formula C187H291N45O59, molecular weight 4113.6 Da.
- Aib8 blocks dipeptidyl peptidase-4 cleavage; the fatty diacid provides reversible albumin binding. Together they extend the reported half-life of the licensed pharmaceutical form to approximately 165 hours.
- Mechanistically, GLP-1R is a class B GPCR that couples to Gs, raising intracellular cyclic AMP; receptor populations are found in pancreatic islets, hindbrain and hypothalamic nuclei, and gastric smooth muscle.
- Semaglutide is surface-active. Foaming, vortexing and repeated freeze–thaw are the leading causes of unexplained potency loss in the laboratory.
- A useful certificate of analysis reports reversed-phase HPLC purity with a chromatogram and a mass-spectrometric identity check against the 4113.6 Da theoretical mass.
What is the semaglutide research peptide?
The semaglutide research peptide is a synthetic 31-residue analogue of human glucagon-like peptide-1, chemically engineered for enzymatic stability and albumin binding, and supplied as lyophilised powder in a sealed vial for laboratory use. It is a selective agonist of the GLP-1 receptor, with no meaningful activity at the GIP or glucagon receptors.
Its design was reported by Lau and colleagues in the Journal of Medicinal Chemistry in 2015, a paper that remains the definitive account of the structure–activity work behind the molecule.2 Semaglutide occupies a particular place in incretin research: it is the best-characterised long-acting GLP-1 mono-agonist, which makes it the natural reference compound whenever a single-receptor signal is required.
It is also the peptide against which the dual and triple agonists are usually benchmarked. Because it engages one receptor and one receptor only, any difference observed between semaglutide and tirzepatide or retatrutide under matched conditions can be attributed to the additional receptor arms — a design logic that only works if the mono-agonist reference is properly characterised.
Structure: sequence, Aib8, Arg34 and the C18 diacid
Semaglutide differs from native GLP-1(7-37) at three points. Two are single-residue substitutions and one is a side-chain acylation. Each solves a specific problem, and understanding which problem each solves explains most of the molecule’s laboratory behaviour.
Aib at position 8
Dipeptidyl peptidase-4 cleaves native GLP-1 between the residues at positions 8 and 9, removing the N-terminal dipeptide and destroying receptor potency. α-Aminoisobutyric acid is alanine with a second methyl group on the α-carbon. That extra bulk makes the peptide a poor DPP-4 substrate without disturbing the receptor-binding conformation.
Arginine at position 34
Native GLP-1 carries lysine at both position 26 and position 34. Since acylation chemistry targets the ε-amine of lysine, having two lysines would produce a mixture of mono-acylated regioisomers. Substituting arginine at 34 leaves a single reactive site, so the fatty acid attaches only at Lys26.
The C18 diacid and its linker
The acyl group is an eighteen-carbon dicarboxylic acid. One carboxyl forms the amide bond to the linker; the other remains free, which improves solubility and modulates albumin affinity. Between the fatty tail and the lysine sit a γ-glutamic acid unit and two AEEA (8-amino-3,6-dioxaoctanoic acid) spacers. The spacers hold the hydrophobic tail away from the receptor-binding face of the peptide.
Semaglutide specification data
The table below lists the verified physicochemical identifiers for semaglutide. These are properties of the molecule and should be confirmed against the mass reported on each batch certificate of analysis.
| Property | Value |
|---|---|
| INN | Semaglutide |
| Development code | NN9535 |
| CAS number | 910463-68-2 |
| Molecular formula | C187H291N45O59 |
| Molecular weight | 4113.6 Da |
| Residue count | 31 (GLP-1(7-37) backbone) |
| Substitutions | Aib8, Arg34 |
| Acylation | C18 fatty diacid at Lys26 |
| Linker | γ-glutamic acid + 2 × AEEA |
| C-terminus | Free acid (Gly37) |
| Receptor target | GLP-1 receptor (class B GPCR) |
| Reported half-life (licensed form) | ≈165 h |
| Physical form | White to off-white lyophilised powder |
| Appearance reconstituted | Clear, colourless solution |
| Typical vial masses | Lyophilised vials, mass stated on label and COA |
Mechanism of action at the GLP-1 receptor
The GLP-1 receptor is a class B G-protein-coupled receptor in the secretin family. Agonist binding stabilises an active conformation that couples predominantly to Gs, activating adenylyl cyclase and raising intracellular cyclic AMP, which in turn engages protein kinase A and the exchange protein Epac2.
Drucker’s review describes the receptor’s tissue distribution and the physiological consequences at each site.1 In pancreatic beta cells, cAMP signalling potentiates glucose-stimulated insulin secretion — the effect is glucose-dependent, because the pathway amplifies rather than initiates secretion. In hindbrain and hypothalamic nuclei, receptor activation is implicated in the regulation of food intake in animal models. In gastric smooth muscle, GLP-1R engagement slows the rate of gastric emptying.
Class B receptor activation follows a two-domain mechanism: the peptide’s C-terminal helix binds the large extracellular domain, and the N-terminus then inserts into the transmembrane bundle to trigger the conformational change. This is why N-terminal integrity matters so much, and why DPP-4 cleavage of just two residues abolishes activity.
Albumin binding and extended persistence
The fatty diacid is a pharmacokinetic device, not a pharmacodynamic one. It does not improve receptor binding; it creates a circulating reservoir. Albumin-bound semaglutide is protected from renal filtration and from enzymatic attack, and it is released slowly as free peptide is cleared.
This has a direct consequence in the laboratory: any assay containing albumin — most notably anything using serum or bovine serum albumin as a carrier — will sequester a fraction of the peptide. Apparent potency can therefore shift substantially with albumin concentration in the buffer. Reporting the albumin content of the assay medium alongside the result is good practice for acylated analogues.
The same amphipathic character explains adsorption losses. In a low-protein buffer, an acylated peptide will bind avidly to polypropylene and glass surfaces, which can silently reduce the effective concentration of a dilute working solution. Low-binding tubes and a small carrier-protein addition are the usual mitigations.
What published research reports
Semaglutide is among the most extensively studied peptides in this class. The literature falls into two useful groups: the medicinal-chemistry and receptor work that explains how the molecule behaves, and the clinical programme of the licensed pharmaceutical form, which is relevant here only as research context.
On the chemistry side, Lau and colleagues reported the design rationale, the effect of each substitution on DPP-4 susceptibility and albumin affinity, and the resulting pharmacokinetic profile.2 On the receptor side, Drucker’s review remains the best synthesis of GLP-1R biology.1
On the clinical side, the STEP 1 trial reported by Wilding and colleagues examined once-weekly semaglutide in 1,961 adults over 68 weeks and reported a mean change in body weight of −14.9% compared with −2.4% in the placebo group.3 A direct randomised comparison against tirzepatide in type 2 diabetes was published by Frías and colleagues, reporting greater HbA1c reduction with tirzepatide across all administered levels.4
These trials describe the licensed pharmaceutical form under controlled clinical conditions. They are cited here to explain why the molecule is of research interest, not as any indication that a research-grade compound behaves equivalently.
Reconstitution and concentration reference
Reconstitution converts a mass into a concentration, and concentration is the only quantity a laboratory record should carry. The procedure below is the standard approach for an acylated peptide.
- Equilibrate. Bring the sealed vial to ambient temperature before removing the flip cap so moisture does not condense onto the lyophilised cake.
- Sanitise the septum. Wipe the rubber stopper with an alcohol swab and allow it to dry before the first puncture.
- Add diluent to the wall. Introduce the measured volume slowly against the inside of the glass, never directly onto the cake.
- Dissolve by inversion. Rotate the vial gently until the solution is clear. Do not shake or vortex — foam indicates surface denaturation.
- Inspect. Confirm the solution is clear and colourless with no particulates or opalescence.
- Aliquot and label. Divide into single-use volumes and record compound, batch, concentration in mg/mL, diluent and date on each.
| Mass in vial | Diluent added | Concentration | Amount per 0.1 mL | Amount per 0.05 mL | Approx. molar concentration |
|---|---|---|---|---|---|
| 2 mg | 1.0 mL | 2.0 mg/mL | 200 mcg | 100 mcg | ≈486 µM |
| 2 mg | 2.0 mL | 1.0 mg/mL | 100 mcg | 50 mcg | ≈243 µM |
| 5 mg | 1.0 mL | 5.0 mg/mL | 500 mcg | 250 mcg | ≈1.22 mM |
| 5 mg | 2.0 mL | 2.5 mg/mL | 250 mcg | 125 mcg | ≈608 µM |
| 5 mg | 2.5 mL | 2.0 mg/mL | 200 mcg | 100 mcg | ≈486 µM |
| 10 mg | 2.0 mL | 5.0 mg/mL | 500 mcg | 250 mcg | ≈1.22 mM |
| 10 mg | 4.0 mL | 2.5 mg/mL | 250 mcg | 125 mcg | ≈608 µM |
| 15 mg | 3.0 mL | 5.0 mg/mL | 500 mcg | 250 mcg | ≈1.22 mM |
Storage, stability and degradation
Lyophilised semaglutide is far more stable than semaglutide in solution. The freeze-dried cake has minimal water activity, which suppresses every hydrolytic degradation route. Once dissolved, all of those routes reopen.
The chemical liabilities in this sequence are the ones common to peptides generally: methionine is absent, but the molecule contains asparagine-free but glutamine-containing regions susceptible to deamidation at elevated pH, and aspartate residues that can undergo isomerisation. Physical degradation — aggregation driven by the hydrophobic acyl chain — is usually the more immediate laboratory concern.
| Form | Condition | Typical handling window | Principal risk |
|---|---|---|---|
| Sealed lyophilised vial | −20 °C, dark | Long term | Moisture ingress if seal compromised |
| Sealed lyophilised vial | 2–8 °C, dark | Medium term | Condensation on repeated warming |
| Sealed lyophilised vial | Ambient, in transit | Short periods only | Cumulative thermal exposure |
| Reconstituted stock | 2–8 °C, dark | Short term | Aggregation, adsorption, microbial ingress |
| Reconstituted aliquot | −20 °C, single use | Per internal stability data | Freeze–thaw aggregation |
| Working dilution in buffer | Ambient during assay | Use immediately | Surface adsorption at low concentration |
Reading a semaglutide certificate of analysis
Two analyses matter most: reversed-phase HPLC for purity and mass spectrometry for identity. For an acylated peptide neither is sufficient alone, because the commonest synthesis defects are invisible to one method and obvious to the other.
On the HPLC trace, look for a single dominant peak with a clean baseline and a reported area percentage. Ask whether the gradient and column are stated — a shallow gradient resolves closely related impurities that a steep one hides. Deletion sequences and incompletely acylated species elute close to the target.
On the mass spectrum, the deconvolved mass should match 4113.6 Da within the stated instrument tolerance. A peptide missing the entire C18-diacid–linker assembly is several hundred daltons lighter; one missing a single AEEA spacer is lighter by roughly 145 Da. Both are readily detected by mass and easily missed by HPLC alone.
Finally, check whether net peptide content is reported. HPLC purity describes the proportion of peptide-related material that is the target; net peptide content describes how much of the vial’s total mass is peptide rather than counter-ion or water. GenoPept publishes per-batch third-party certificates at the COA certificates page, and our guide to reading a COA walks through each field.
Semaglutide in the GenoPept store
Frequently asked questions
What is the molecular weight of semaglutide?
Semaglutide has a molecular weight of 4113.6 Da and the molecular formula C187H291N45O59, with CAS number 910463-68-2. That mass includes the C18 fatty diacid and its γGlu–AEEA–AEEA linker, which together account for several hundred daltons. Confirming the deconvolved mass against 4113.6 Da is the single most useful identity check on a certificate of analysis.
What is Aib8 in semaglutide and why does it matter?
Aib is α-aminoisobutyric acid, a non-natural amino acid equivalent to alanine with an extra methyl group on the α-carbon. Placed at position 8 — the site where dipeptidyl peptidase-4 cleaves native GLP-1 — it makes the peptide a poor enzyme substrate while leaving receptor binding essentially intact. Without it, the molecule would survive only a few minutes.
Why is semaglutide’s half-life so long?
Two features combine. Aib8 prevents enzymatic cleavage, and the C18 fatty diacid on Lys26 binds serum albumin reversibly, creating a slowly released circulating reservoir that is also shielded from renal filtration. The reported half-life of the licensed pharmaceutical form is approximately 165 hours, roughly one week, compared with about two minutes for native GLP-1.
How is semaglutide reconstituted for laboratory use?
Bring the sealed vial to ambient temperature, sanitise the stopper, then add the measured diluent slowly down the inside wall of the vial rather than onto the cake. Dissolve by gentle inversion — never shaking or vortexing, which causes foaming and surface denaturation. Inspect for clarity, then aliquot into single-use volumes and label each with concentration, diluent and date.
Does semaglutide need to be refrigerated?
Sealed lyophilised vials are normally held at 2–8 °C for medium-term storage and at −20 °C for long-term storage, in both cases protected from light. They tolerate short ambient periods during transit. Reconstituted solution is considerably less stable and should be refrigerated, protected from light and used within the window supported by your own stability data.
Why does semaglutide solution foam when shaken?
Because the C18 fatty diacid makes the molecule amphipathic — it has both hydrophobic and hydrophilic regions, so it accumulates at the air–liquid interface. Shaking creates enormous interfacial area, and peptide adsorbed there partially unfolds and aggregates. The resulting foam represents real loss of monomeric peptide, which is why gentle inversion is the only acceptable mixing method.
What should a semaglutide certificate of analysis show?
Reversed-phase HPLC purity with the chromatogram and stated method conditions, plus mass-spectrometric identity confirming a deconvolved mass of 4113.6 Da within instrument tolerance. Appearance, batch number and analysis date should also appear. Net peptide content is a valuable addition, since it separates true peptide mass from counter-ion and residual water.
Is semaglutide from GenoPept suitable for human use?
No. Semaglutide supplied by GenoPept is a research chemical for in-vitro laboratory and analytical work only. It is not a medicine, is not manufactured to pharmaceutical standards, and must not be used for human or veterinary purposes or for the diagnosis, treatment or prevention of any condition. Purchasers must be qualified researchers or institutions.
References
- Drucker DJ. Mechanisms of Action and Therapeutic Application of Glucagon-like Peptide-1. Cell Metabolism. 2018;27(4):740–756. PubMed
- Lau J, Bloch P, Schäffer L, et al. Discovery of the Once-Weekly Glucagon-Like Peptide-1 (GLP-1) Analogue Semaglutide. Journal of Medicinal Chemistry. 2015;58(18):7370–7380. Publisher
- Wilding JPH, Batterham RL, Calanna S, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity. New England Journal of Medicine. 2021;384:989–1002. PubMed
- Frías JP, Davies MJ, Rosenstock J, et al. Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes. New England Journal of Medicine. 2021;385:503–515. PubMed
- Coskun T, Sloop KW, Loghin C, et al. LY3298176, a novel dual GIP and GLP-1 receptor agonist for the treatment of type 2 diabetes mellitus: from discovery to clinical proof of concept. Molecular Metabolism. 2018;18:3–14. PubMed
- Willard FS, Douros JD, Gabe MB, et al. Tirzepatide is an imbalanced and biased dual GIP and GLP-1 receptor agonist. JCI Insight. 2020;5:e140532. PubMed
Research-grade semaglutide, batch-verified
GenoPept supplies semaglutide as lyophilised vials with a per-batch third-party certificate of analysis covering HPLC purity and mass-spectrometric identity, dispatched from the UK strictly for laboratory research.