What semaglutide is
Semaglutide is a long-acting, acylated analogue of human glucagon-like peptide-1 (GLP-1). It was developed by Novo Nordisk under the developer codes NN9535 and NNC 0113-0217 for the injectable form, and NN9924 / OG217SC for the oral form. Its Anatomical Therapeutic Chemical (ATC) classification code is A10BJ06.
Mechanistically, semaglutide is a selective GLP-1 receptor (GLP-1R) agonist — a single-receptor agonist that acts on one target. It is not a dual or triple agonist. For a broader primer on this peptide class and how GLP-1 receptor signalling works, see GLP-1 explained.
Semaglutide is approved as a medicine under several brand names: Ozempic (type 2 diabetes, subcutaneous), Wegovy (obesity, subcutaneous) and Rybelsus (an oral once-daily tablet co-formulated with the SNAC absorption enhancer). RetaLABS supplies only the research-grade compound, which is a distinct category from the approved therapeutic products. This page is a molecular and scientific reference intended for researchers. It is for research use only and is not medical advice or a treatment recommendation. For an orientation to the compound in a research context, see the semaglutide research guide.
Molecular structure and amino acid sequence
Semaglutide is a 31-amino-acid peptide built on a modified GLP-1[7-37] backbone. Its one-letter amino acid sequence is:
HXEGTFTSDVSSYLEGQAAKEFIAWLVRGRG — where X = Aib (2-aminoisobutyric acid) at position 2.
Three deliberate structural modifications distinguish semaglutide from native human GLP-1(7-37):
- Ala8 → Aib: alanine at position 8 is replaced by 2-aminoisobutyric acid (Aib), conferring resistance to dipeptidyl peptidase-4 (DPP-4) cleavage.
- Lys34 → Arg34: the lysine at position 34 is replaced by arginine, leaving a single lysine and thereby forcing a single, defined acylation site.
- Acylation at Lys26: the side chain of the remaining lysine (Lys26 in GLP-1 numbering) is acylated with a C18 fatty diacid (octadecanedioic acid) via a gamma-glutamate linker plus two AEEA (2-(2-aminoethoxy)ethoxy)acetyl) spacers, enabling albumin binding.
The fatty acid moiety is C18 (octadecanedioic acid). The C-terminus of the peptide is a free carboxylic acid (free acid) and is not amidated. These features together define the molecule's pharmacokinetic behaviour, discussed below.
Physicochemical properties
The table below summarises the confirmed physicochemical and identifier data for semaglutide. The headline molecular weight is the average molecular weight; the monoisotopic mass is listed separately and explicitly labelled so the two are never confused.
| Property | Value |
|---|---|
| Compound name | Semaglutide |
| Developer codes | NN9535 / NNC 0113-0217 (injectable); NN9924 / OG217SC (oral) |
| ATC code | A10BJ06 |
| CAS Registry Number | 910463-68-2 (parent / free-acid form) |
| Molecular formula | C187H291N45O59 (free acid) |
| Average molecular weight | 4113.58 g/mol |
| Monoisotopic mass | ~4111.12 Da (monoisotopic mass, per label) |
| Peptide length | 31 amino acids (modified GLP-1[7-37] backbone) |
| C-terminus | Free carboxylic acid (not amidated) |
| Acylation | C18 fatty diacid via gamma-Glu linker + 2 AEEA spacers at Lys26 |
| Class | Long-acting acylated GLP-1 analogue; selective GLP-1R agonist |
| PubChem CID | 56843331 |
| ChEMBL ID | CHEMBL2108724 |
| UNII | 53AXN4NNHX |
| ChEBI ID | CHEBI:167574 |
This reference does not assert solubility or storage specifications. For laboratory handling, reconstitution and storage of research-grade peptides, see the peptide reconstitution and storage guide.
Pharmacokinetics and half-life extension
Semaglutide has a plasma half-life of approximately one week (roughly 7 days, about 165 hours). This extended half-life is a direct consequence of the structural modifications described above and underpins the once-weekly subcutaneous dosing of the approved injectable brands (Ozempic, Wegovy); the approved oral brand (Rybelsus) is taken as a once-daily tablet.
Two design features drive the prolonged half-life. First, the Aib substitution at position 8 protects the peptide from rapid DPP-4 degradation that limits the action of native GLP-1. Second, the C18 fatty-diacid acylation at Lys26 — attached through a gamma-glutamate linker and two AEEA spacers — promotes strong, reversible binding to serum albumin. Albumin binding reduces renal clearance and acts as a circulating reservoir, slowing the molecule's elimination and extending systemic exposure.
The arginine substitution at position 34 ensures the fatty-acid chain attaches at a single, defined lysine, giving a homogeneous, well-characterised acylation profile. Together these modifications convert a short-lived native peptide into a long-acting analogue. For research-context dosing frameworks, see the semaglutide dosing protocol. This information is provided for research reference only and is not a human dosing recommendation.
Structure to mechanism
The molecular architecture of semaglutide maps directly onto its mechanism. The GLP-1[7-37] backbone preserves the recognition elements needed to engage and activate the GLP-1 receptor, while the engineered modifications (Aib8, Arg34 and the Lys26 acylation) tune stability and circulating duration without changing the single-receptor selectivity of the molecule. Semaglutide remains a selective, single-receptor GLP-1R agonist.
Because it acts on only one receptor, semaglutide is mechanistically distinct from newer multi-receptor agonists. For a structural and pharmacological comparison against a multi-target peptide, see retatrutide vs semaglutide.
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