Semaglutide

Overview

Semaglutide is a synthetic analogue of glucagon-like peptide-1, engineered for a duration of action measured in days rather than minutes. It is among the most thoroughly characterised compounds in this catalogue, with a published record spanning discovery chemistry, pharmacokinetics and large randomised trials.

It also occupies a different position from almost everything else here, and that difference should be stated at the outset rather than buried: semaglutide is an approved medicine. That has implications covered in the regulatory section below.

Chemical identity

• CAS number: 910463-68-2
• Molecular formula: C₁₈₇H₂₉₁N₄₅O₅₉
• Molecular weight: 4113.58 g/mol
• Classification: GLP-1 receptor agonist, acylated peptide analogue
• Length: 31 residues plus the acylation chain
• Appearance: White lyophilised powder

At 4,114 g/mol the molecule is far past the point where a two-dimensional depiction is legible at reading size, so its architecture is described rather than drawn. Note the absence of sulfur in the formula: there is no cysteine and no methionine, which has consequences for stability discussed under handling.

Where it comes from

Glucagon-like peptide-1 is an incretin — a hormone released by intestinal cells in response to food, which signals to the pancreas that nutrients are arriving. Its actions include stimulating insulin secretion in a glucose-dependent manner, suppressing glucagon, slowing gastric emptying and promoting satiety through receptors in the brain.

Native GLP-1 has an obvious limitation as a research or therapeutic tool: it is destroyed almost immediately. Dipeptidyl peptidase-4 cleaves it near the N-terminus within about two minutes of release. The hormone is designed to be a brief postprandial signal, not a sustained one.

Every GLP-1 analogue exists to solve that problem, and they differ mainly in how thoroughly they solve it.

The three modifications

Semaglutide differs from native GLP-1 in three deliberate ways, each addressing a specific route of loss:

• Position 8: alanine replaced by Aib. 2-aminoisobutyric acid is a non-standard amino acid with an extra methyl group on its central carbon. That bulk blocks DPP-4 from cleaving the peptide — the single most important change, addressing the two-minute problem directly.
• Position 34: lysine replaced by arginine. Not a stability change but a chemical one. The acylation in the next point attaches to a lysine side chain, and removing the second lysine ensures it attaches at one defined position rather than either of two.
• Position 26: acylation with a C18 diacid. A fatty diacid chain attached through a spacer, giving reversible binding to albumin in circulation. Bound peptide is shielded from renal filtration and from enzymatic degradation, and releases gradually.

Together these take the half-life from roughly two minutes to roughly a week — a change of about three orders of magnitude, achieved by three substitutions.

Two ways to bind albumin

Albumin binding appears twice in this catalogue, achieved by chemistries that are worth contrasting because the difference is instructive.

CJC-1295 with DAC uses a maleimide group that forms a covalent bond with a specific cysteine on albumin. The attachment is permanent: peptide and protein become one molecule.

Semaglutide’s fatty diacid binds non-covalently and reversibly. The chain inserts into a hydrophobic pocket on albumin and is held there by the same forces that bind fatty acids generally, in a continuous equilibrium of binding and release.

The practical consequences differ. A covalent conjugate lasts as long as the albumin molecule it is attached to. A reversible association maintains a small free fraction available to reach receptors, with the bound majority acting as a reservoir. Both extend duration dramatically; one creates a permanent conjugate, the other a buffered supply.

The same reversible strategy appears in cagrilintide, which is part of why the two compounds share a dosing cadence and are studied together.

Mechanism of action

Semaglutide agonises the GLP-1 receptor, a G-protein coupled receptor expressed in pancreatic beta cells, in the gastrointestinal tract and in regions of the brain involved in appetite regulation. Signalling proceeds through cyclic AMP.

A feature of the underlying biology worth noting is that GLP-1’s effect on insulin secretion is glucose-dependent: the receptor amplifies insulin release when glucose is elevated, and does comparatively little when it is not. That dependence is intrinsic to the pathway rather than engineered into the analogue.

Research record

The published record here is the most extensive of any compound in this catalogue, and unusually it includes the discovery chemistry as well as the outcomes.

• Design and discovery. Lau and colleagues published the medicinal chemistry behind the molecule, describing the reasoning that produced the three modifications above.
• Cardiovascular outcomes. Large randomised trials examined outcomes in populations with type 2 diabetes over multi-year follow-up.
• Body weight. A separate randomised programme examined effects on body weight in populations with overweight and obesity.

For a research setting, the relevant point is that pharmacokinetics, dose–response relationships and adverse event profiles are documented in peer-reviewed literature at a level of detail that no other compound here approaches.

Reported observations

The effects most consistently reported across trials are gastrointestinal — nausea, vomiting, diarrhoea and constipation — generally described as dose-related and most pronounced during escalation. The trial literature also documents less common findings including gallbladder-related events and pancreatitis, and carries warnings derived from rodent studies regarding thyroid C-cell tumours.

Unlike most compounds in this catalogue, these are not inferences from small preclinical studies. They come from large controlled trials with systematic adverse event collection, which makes them considerably more reliable than the equivalent statements elsewhere on this site.

Regulatory status

Semaglutide is an approved prescription medicine in the United States, the European Union and many other jurisdictions, marketed under brand names for type 2 diabetes and for weight management. This distinguishes it from every other compound in this catalogue except in degree.

Two consequences follow, and both matter.

First, material supplied for laboratory research is not a pharmaceutical product. It has not been manufactured, tested, or released under the controls that apply to an approved medicine, and it is not a substitute for one. Anyone whose interest in semaglutide is medical should be speaking to a clinician, not reading a research catalogue.

Second, the existence of an approved product means the compound’s clinical properties are established through proper trials. Nothing on this page should be read as suggesting that research material offers those properties.

Handling, reconstitution and storage

• Lyophilised storage: sealed, refrigerated, protected from light. Freeze for long-term storage.
• No oxidation-prone residues. The formula contains no sulfur — no methionine, no cysteine — so the most common chemical degradation route for peptides does not apply.
• The acylation is surface-active. The fatty acid chain that binds albumin also makes the molecule prone to adsorbing onto container surfaces and to foaming. Do not shake; foaming denatures acylated peptides particularly readily.
• Reconstitution: add diluent slowly down the vial wall and allow the powder to dissolve undisturbed.
• After reconstitution: refrigerate, protect from light, minimise freeze–thaw cycles.
• Concentration: our peptide reconstitution calculator converts vial quantity, diluent volume and syringe size into concentration per unit.

Purity and analytical verification

This is a demanding synthesis: a 31-residue backbone, a non-standard amino acid at position 8, a site-specific acylation with a spacer, and a substitution at position 34 whose entire purpose is to make that acylation unambiguous. Each of those is a point at which a batch can be wrong in a way that is not visually obvious.

Two checks matter most.

Mass confirmation for the acylation. A batch in which acylation failed or ran incompletely is missing a substantial, well-defined mass. That is straightforward to detect — but only if someone compares the measured mass against the expected 4,114 g/mol rather than merely noting that a peptide is present. An unacylated backbone would be a fundamentally different molecule pharmacologically, with a half-life of minutes rather than days.

HPLC purity. Thirty-one coupling steps generate deletion sequences, and the acylation chemistry adds further related impurities. Purity figures for a molecule of this complexity represent significantly more purification work than for a short peptide.

We publish third-party certificates of analysis by batch.

References

• 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. PMID 26308095
• Marso SP, Bain SC, Consoli A, et al. Semaglutide and cardiovascular outcomes in patients with type 2 diabetes. New England Journal of Medicine, 2016. PMID 27633186
• Wilding JPH, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity. New England Journal of Medicine, 2021. PMID 33567185

Summary

Semaglutide is an acylated GLP-1 receptor agonist, CAS 910463-68-2, molecular formula C₁₈₇H₂₉₁N₄₅O₅₉, molecular weight 4,113.58 g/mol. Three modifications to native GLP-1 — a non-standard amino acid at position 8 blocking DPP-4 cleavage, a substitution at 34 directing acylation to a single site, and a fatty diacid at 26 giving reversible albumin binding — extend the half-life from about two minutes to about a week. It is an approved prescription medicine in many jurisdictions, with a clinical trial record far exceeding anything else in this catalogue, and research-grade material is not a substitute for that product.

For laboratory research use only. Not for human consumption. This material is not a drug, food, or cosmetic and may not be sold or used for any purpose other than in vitro or non-human laboratory research. References to clinical studies describe the published scientific literature and are not guidance for use.