Semax vs Selank: The Chemistry, Compared
Two heptapeptides that share a C-terminal Pro-Gly-Pro sequence and a Moscow research origin, but come from entirely different parent molecules — set side by side on identity alone.
This article compares Semax and Selank on chemical identity only — sequence, structure, and verified identifiers. It does not describe, and should not be read as describing, any biological effect, use, or application of either compound in a person or animal. All products supplied by Velyx Research Ltd are for laboratory research purposes only and are not intended for human or animal use.
Semax and Selank get grouped together constantly — both heptapeptides, both developed at Russia's Institute of Molecular Genetics, both sold in the same "nootropic peptide" breath online. Grouped that closely, it's easy to miss that they're built from two completely unrelated parent sequences. This article sets out the chemistry: what each molecule actually is, how their structures differ, and what those structural differences mean at the molecular level — nothing about biological activity in either case.
What Is Semax?
Semax is a synthetic heptapeptide: Met-Glu-His-Phe-Pro-Gly-Pro. Structurally, it's built from the fourth-to-seventh residues of adrenocorticotropic hormone (ACTH(4-7): Met-Glu-His-Phe) with a Pro-Gly-Pro tripeptide appended to the C-terminus. It is catalogued under PubChem as "ACTH (4-7), Pro-Gly-Pro-."
What Is Selank?
Selank is also a synthetic heptapeptide: Thr-Lys-Pro-Arg-Pro-Gly-Pro. It's built from the full four-residue sequence of tuftsin (Thr-Lys-Pro-Arg), a fragment of the immunoglobulin G heavy chain, with the same Pro-Gly-Pro tripeptide appended to the C-terminus. It carries the development code TP-7 in the original research literature.
Identifiers, Side by Side
| Property | Semax | Selank |
|---|---|---|
| Sequence | Met-Glu-His-Phe-Pro-Gly-Pro | Thr-Lys-Pro-Arg-Pro-Gly-Pro |
| Parent fragment | ACTH(4-7) | Tuftsin (Thr-Lys-Pro-Arg) |
| Parent molecule class | Melanocortin/corticotropin family | Immunoglobulin-derived peptide |
| Molecular formula | C₃₄H₅₁N₉O₁₀S | C₃₃H₅₄N₁₁O₉ |
| Molecular weight | ≈813.9 g/mol | ≈751.9 g/mol |
| CAS number | 80714-61-0 | 129954-34-3 |
| PubChem CID | 9811102 | 11765600 |
| Development origin | Institute of Molecular Genetics, Russian Academy of Sciences | Institute of Molecular Genetics, Russian Academy of Sciences |
What the Two Structures Have in Common
Both sequences terminate in the same tripeptide: Pro-Gly-Pro. That shared C-terminal motif is a genuine structural link between the two molecules, distinct from their unrelated N-terminal fragments (ACTH-derived for Semax, tuftsin-derived for Selank). Pro-Gly-Pro is a naturally occurring collagen-breakdown tripeptide in its own right, and its inclusion at the C-terminus of both molecules is a shared design choice in the underlying chemistry rather than a coincidence of sequence.
Where the Structures Diverge
Past that shared tail, the two molecules have little in common structurally:
- Sulphur content. Semax's N-terminal methionine residue is the only sulphur-containing residue in either molecule. Selank's sequence contains no methionine and no sulphur at all — its N-terminal threonine and internal lysine and arginine residues are all sulphur-free.
- Nitrogen content. Selank's formula carries eleven nitrogen atoms against Semax's nine, a direct consequence of the guanidino group on arginine and the additional amine on lysine — neither of which appears anywhere in Semax.
- Oxygen content. Semax carries ten oxygens to Selank's nine, reflecting the extra carbonyl contributed by proline substitution patterns and the phenylalanine/histidine side chains in place of arginine/lysine.
- Molecular weight. Semax is the heavier molecule by roughly 62 g/mol, driven by histidine and phenylalanine's larger ring-containing side chains compared with lysine and arginine's chain-based ones.
The practical takeaway for anyone comparing the two on a spec sheet: "Russian peptide" is not a chemistry classification. Semax and Selank belong to two different parent-peptide families entirely, and any similarity in how they're marketed shouldn't be read as similarity in structure.
Manufacturing & Verification
Both are produced via solid-phase peptide synthesis, assembled one residue at a time against a defined sequence — standard practice for short synthetic peptides rather than an extraction process from any natural source. Identity for both is confirmed via mass spectrometry (matching the expected molecular weight) and purity via reversed-phase HPLC, the same two methods used across the research-peptide field generally and not specific to either compound.
UK Regulatory Considerations
The regulatory position of research peptides in the UK can depend on the specific substance, its intended purpose, how it is presented or marketed, and the legislation that applies.
Semax and Selank are supplied by Velyx Research Ltd exclusively for laboratory research purposes. They are not supplied as medicines or for human or veterinary use, and Velyx does not make therapeutic or clinical claims about either compound.
Research-use-only wording communicates the intended purpose of the products, but does not by itself determine their legal or regulatory status. Researchers are responsible for ensuring that their activities comply with any requirements applicable to their research programme.
Where a specific regulatory determination is required, appropriate professional advice should be obtained.
In Summary
Semax and Selank share a research origin and a C-terminal Pro-Gly-Pro motif, and that's where the resemblance ends. One is built from an ACTH fragment and carries sulphur; the other is built from tuftsin and doesn't. Treating them as interchangeable because they're often sold side by side skips over the fact that, structurally, they're built from two unrelated starting sequences.
All products referenced are supplied strictly for laboratory and research purposes only. They are not intended for human or veterinary use, diagnosis, treatment, or prevention of any disease. Velyx Research Ltd — Registered in England & Wales, Company No. 03697395.
Frequently Asked Questions
Common research questions about Semax and Selank.
They're built from two unrelated parent fragments — Semax from ACTH(4-7), Selank from tuftsin — and differ in sulphur content, nitrogen content, and molecular weight. The only structural feature they share is a C-terminal Pro-Gly-Pro tripeptide.
No. Semax derives from the melanocortin/corticotropin family (ACTH). Selank derives from an immunoglobulin-derived peptide (tuftsin). Being grouped together as "Russian peptides" online reflects their shared research origin, not a shared chemical class.
Semax, at roughly 813.9 g/mol versus Selank's roughly 751.9 g/mol — a difference of about 62 g/mol, mainly attributable to phenylalanine and histidine's larger side chains in Semax versus lysine and arginine in Selank.
Semax's sequence includes methionine, the only sulphur-containing amino acid in either molecule's sequence. Selank's sequence has no methionine and no other sulphur-containing residue, so its formula contains no sulphur at all.
Neither Semax nor Selank has UK Marketing Authorisation from the MHRA. Both are supplied strictly for laboratory research purposes and are not licensed medicines.
All products sold by Velyx Research Ltd are for research purposes only and are not intended for human consumption. Velyx Research Ltd — Registered in England & Wales · Company No. 03697395
References
- PubChem records and chemical identifiers referenced in the article.
- Original research literature relating to Semax and Selank chemical identity and development.