Semax in Canada: Structure, Oxidation and Testing for Research Labs

Most enquiries about Semax in Canada come from labs that already know the compound’s reputation as a short ACTH-derived peptide and want to know what they are actually receiving. The answer is a seven-residue chain with one feature that dominates its quality control: a methionine at the N-terminus. That single residue explains the impurity most likely to appear on a certificate, why a lot can change after it has been tested, and how a multi-vial order should be stored. This guide covers the structure first and the practical consequences after.

Semax in Canada: what research labs are ordering

Semax is the heptapeptide Met-Glu-His-Phe-Pro-Gly-Pro, written MEHFPGP in one-letter code. It came out of Russian peptide research and is studied in the literature mainly as a fragment of adrenocorticotropic hormone (ACTH) that no longer carries ACTH’s hormonal activity at the adrenal receptor. For a buyer, the headline figures are:

The single sulfur atom in the formula belongs to the methionine, and it is the atom to keep in mind for everything that follows.

From ACTH to seven residues

Catalogue copy often calls Semax an ACTH(4-10) analog. That is only partly right. Laying the two sequences next to each other shows which residues were kept and which were swapped out.

The first four residues match ACTH positions 4 to 7 exactly. The arginine, tryptophan and glycine that follow in the hormone are gone, replaced by a synthetic Pro-Gly-Pro tail. The most precise shorthand is therefore ACTH(4-7)-PGP. When you see ACTH(4-10) on a label, read it as a description of the region Semax was designed from rather than its composition.

Why the Pro-Gly-Pro tail was added

Very short linear peptides are cleared quickly by exopeptidases, enzymes that trim residues from either end of a chain. Proline is awkward for most of them. Its side chain loops back and bonds to its own backbone nitrogen, forming a ring that restricts the chain’s shape and resists cleavage at the adjacent bonds. Capping a fragment with Pro-Gly-Pro is a known way of making it last long enough to study in enzyme-containing systems.

The same tail appears on Selank, where it is attached to tuftsin, a completely unrelated tetrapeptide. The shared tail is a design choice, not evidence that the two compounds are related. Our companion article on Selank and tuftsin covers the other side of that pairing.

Methionine oxidation and the +16 Da peak

The sulfur in methionine’s side chain reacts readily with oxygen, light-generated radicals and peroxides, forming methionine sulfoxide. The change adds one oxygen atom, so the oxidised peptide weighs 16 Da more than the parent. Further oxidation to the sulfone (+32 Da) is possible but much less common under ordinary handling.

For Semax, this is the impurity most worth watching. Three points follow for a QC reviewer:

• It is a different molecule. A peak near 829.9 on the mass spectrum is not the labelled compound, even though it differs by a single atom.
• It can form after testing. A certificate that shows no oxidised species describes the material on the test date. Storage and handling decide what happens next.
• It usually elutes slightly earlier. The sulfoxide is more polar, so on reversed-phase HPLC it tends to show as a leading shoulder or a small peak just before the main one. A shallow gradient separates it more clearly than a fast one.

Losing ACTH’s tryptophan did remove one oxidation route, since tryptophan is also easily oxidised. That leaves the methionine as the main site to protect. Our article on how peptides degrade explains the wider chemistry.

Choosing a detection wavelength

Semax has only one aromatic residue, the phenylalanine, and phenylalanine absorbs weakly at 280 nm. That makes 280 nm a poor choice for purity work on this compound, because the peptide and many possible impurities give very little signal there. The informative wavelength is in the 210 to 220 nm range, where the peptide bond itself absorbs and every peptide-containing species is visible. A Semax certificate should state the wavelength, and a figure measured near 214 nm carries far more weight than one measured at 280 nm.

Name variants and identity checks

Semax is sold under its own name, as the sequence MEHFPGP, and in modified forms. The modified forms matter, because they are different molecules with different masses. A version sold as N-acetyl Semax amidate, for example, carries an acetyl group on the N-terminus (adding about 42 Da) and a C-terminal amide (removing about 1 Da), so its mass sits well above 813.9. If a certificate shows a mass that does not match the table above, check whether a modified variant was supplied before assuming a synthesis problem.

Receiving and storing a Semax order

For a lab drawing on one lot over several months, controlling air exposure is most of the job. A practical routine for a multi-vial shipment:

1. Confirm the certificate mass is 813.9 and note whether an oxidised species is reported at 829.9.
2. Match each vial’s cap and crimp colour to its certificate and log the pairing with the lot.
3. Store unopened vials cold, dry and dark, and let each vial reach room temperature before opening to avoid condensation.
4. Open only the vials a given analysis needs, so the rest of the lot stays sealed.
5. Prepare analytical solutions in fresh, peroxide-free solvents and do not leave them standing open.
6. If the lot is re-tested later, compare the +16 Da signal with the original certificate.

We stock Semax 10mg vials, shipped from within Canada, and volume pricing is mix-and-match, so Semax and Selank vials count toward the same break. Products are third-party tested for purity by HPLC, and certificates are published for some products on our certificates of analysis page. The net peptide content guide explains why the peptide mass in a vial is lower than its gross weight.

Semax is supplied by Bulk Peptides for in-vitro laboratory research only. It is not a drug or health product, and it is not sold for use in humans or animals.