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Molecular Weight
Purity
Storage
Appearance
Solubility
01
Semaglutide is a 31-residue synthetic analogue of glucagon-like peptide-1, GLP-1(7–37). It differs from the native hormone in three ways: α-aminoisobutyric acid (Aib) at position 2, arginine in place of lysine at position 28, and a C18 fatty diacid attached to the remaining lysine (Lys20) through a γ-glutamate and two AEEA (OEG) spacers.
The Aib residue protects against DPP-IV, and the lipid enables strong binding to serum albumin. Semaglutide is a selective GLP-1 receptor agonist, which makes it the single-receptor reference against which dual agonists such as tirzepatide and triple agonists such as retatrutide are compared. It is supplied as a lyophilized reference material for in vitro GLP-1 receptor studies and for developing analytical methods for lipidated peptides.
02
Semaglutide keeps the GLP-1 backbone and adds targeted modifications.
Aib2
α-Aminoisobutyric acid replaces alanine at position 2. Its two methyl groups block DPP-IV cleavage after residue 2 and favour the helical N-terminal structure needed for receptor activation.
Arg28
Lysine is replaced by arginine at position 28 (Lys34 in GLP-1 numbering), leaving Lys20 as the only lysine so the lipid can be attached at a single, defined site.
Lipidated Lys20
The side-chain amine of Lys20 carries octadecanedioic acid (C18 diacid) via γ-glutamic acid and two 8-amino-3,6-dioxaoctanoic acid (AEEA/OEG) units. The free carboxylate at the end of the diacid adds a negative charge and is important for albumin binding.
Free-acid C-terminus
The chain ends in Gly31-OH, mirroring native GLP-1(7–37), rather than the amidated ends of tirzepatide and retatrutide.
Aromatic residues
Phe6, Tyr13, Phe22 and Trp25 allow UV detection at 280 nm as well as 214 nm.
03
In vitro, semaglutide is characterised as a potent and selective GLP-1 receptor agonist.
GLP-1 receptor activity
Competition binding with labelled GLP-1 or exendin-4 and cAMP accumulation assays in GLP-1R-expressing cells measure its affinity and potency relative to native GLP-1 and earlier analogues such as liraglutide.
Albumin binding
Surface plasmon resonance and calorimetry studies characterise how the C18 diacid binds the fatty-acid sites of human serum albumin. As with other lipidated peptides, measured potency shifts with the albumin content of the assay.
Selectivity
Unlike tirzepatide and retatrutide, semaglutide shows no meaningful activity at the GIP or glucagon receptors, making it the GLP-1R-selective comparator in multi-receptor panels.
All observations described here come from cell-free and cell-based in vitro systems.
04
Lipidated peptide HPLC
A widely used benchmark for developing and checking reversed-phase methods for acylated peptides, including column performance and recovery.
Incretin receptor panels
The selective GLP-1R reference alongside dual (tirzepatide) and triple (retatrutide) agonists when calculating selectivity ratios.
Acylation-site mapping
Enzymatic digestion followed by LC-MS/MS locates the lipid on Lys20 and measures the non-acylated impurity.
Stability-indicating methods
Its known degradation products, including Trp25 oxidation, deamidation, aspartate isomerisation and the des-lipid form, serve as markers when validating methods for acylated GLP-1 analogues.
05
Storage
Store the lyophilized powder at −20 °C, sealed, desiccated and protected from light. Let the vial reach room temperature before opening to avoid condensation.
Solubility and pH
Semaglutide is least soluble near its isoelectric point (roughly pH 4–6). A neutral to slightly basic aqueous buffer, or DMSO for stock solutions, dissolves it more reliably. For direct-infusion MS, an acetonitrile/water mixture with formic acid is commonly used.
Light sensitivity
Trp25 can photo-oxidise. Use amber or foil-wrapped containers and handle under subdued light.
Deamidation
Gln17 can deamidate slowly in solution. Freeze reconstituted aliquots and limit how long solutions are kept.
Surface adsorption
The lipid chain promotes binding to glass and untreated plastics. Use low-binding polypropylene tubes and tips.
06
Analytical methods must account for both the peptide and its lipid modification.
HPLC
Wide-pore (300 Å) C4 or C8 columns at elevated temperature usually give the best peak shape; C18 can be used but needs stronger organic conditions. Exact conditions are set during method development.
Mass spectrometry
ESI-MS in positive mode shows charge states around +3 to +6; deconvolution should give 4113.58 Da. Formic acid is preferred over TFA for LC-MS.
Acylation site
Digestion followed by LC-MS/MS of the fragment containing Lys20 confirms the attachment site and the full C18 diacid–γGlu–2×AEEA linker. The des-lipid peptide is the main synthesis-related impurity.
Impurity profile
Typical checks include the des-lipid form, Trp25 oxidation (+16, +32 Da), Gln17 deamidation (+1 Da), Asp9 isomerisation (isoAsp, same mass but different retention) and the C-terminally amidated variant (about −1 Da).
07
Semaglutide carries a C18 fatty diacid; tirzepatide and retatrutide carry C20 diacids. All three use a γ-glutamate-based linker to a lysine side chain, but the chain length, linker details and attachment position differ, which changes their chromatographic retention and albumin binding.
It is modelled on native GLP-1(7–37), which ends in glycine with a free carboxylic acid. The free acid is about 1 Da heavier than an amidated version, which helps distinguish the two by mass spectrometry.
It is selective for the GLP-1 receptor, with no meaningful activity at the GIP or glucagon receptors. Tirzepatide adds GIP receptor activity, and retatrutide adds both GIP and glucagon receptor activity.
By reversed-phase HPLC, ideally on a wide-pore C4 or C8 column at elevated temperature. The lipid makes intact semaglutide much more hydrophobic than the des-lipid peptide, so the two separate well.
Deamidation adds about 1 Da, so it is quantified by high-resolution LC-MS, often after enzymatic digestion, using the fragment containing position 17. Optimised HPLC can also separate the deamidated forms from the main peak.
Avoid the range around its isoelectric point, roughly pH 4–6, where solubility is lowest. Neutral to slightly basic buffers, or DMSO for stock solutions, work better.
This material is not. Although semaglutide is the active ingredient of approved medicines, the material listed here is supplied strictly as a reference compound for laboratory and analytical research and is not for human or animal use.
Semaglutide Research Reference. (2026). Pure Peptides Labs Research Catalogue. Retrieved from https://purepeptideslabs.net/research-catalogue/metabolic-research-peptides/semaglutide/
Materials listed on this platform are supported by independent testing and published documentation for laboratory research contexts.
