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Research use only
· 7 min read
Two heptapeptides, one originating laboratory, and a habit of being filed together as "the Russian peptides" - which flattens the one thing that actually separates them. Semax and Selank are both seven residues long and both came out of the Institute of Molecular Genetics in Moscow, but they descend from completely different parent molecules: Semax from the ACTH / melanocortin family, Selank from the immunopeptide tuftsin. Same length, same birthplace, unrelated ancestry. Everything below describes what published studies have investigated, grouped strictly by molecular lineage and receptor pharmacology, not any human use. Kovalabs supplies Semax and Selank strictly as research reagents for laboratory and in-vitro research only.
Semax is the heptapeptide Met-Glu-His-Phe-Pro-Gly-Pro - the ACTH(4-7) core extended at the C-terminus by a Pro-Gly-Pro tail, which is the documented design move that buys resistance to the peptidases that otherwise clip short ACTH fragments in minutes. By sequence homology it sits in the melanocortin peptide family as an analogue of the ACTH(4-10) fragment. Its molecular formula is C37H51N9O10S, average molecular weight 813.9 g/mol, CAS 80714-61-0, PubChem CID 9811102, InChIKey AFEHBIGDWIGTEH-AQRCPPRCSA-N. The single sulphur atom in that formula belongs to the N-terminal methionine and is the reason Semax is oxidation-prone - a handling detail, not a biological one. The full identity record and study designs live in the Semax research monograph; this page is about how it contrasts with Selank.
Selank is the heptapeptide Thr-Lys-Pro-Arg-Pro-Gly-Pro (TKPRPGP), development code TP-7. Its design rationale is almost comically literal: tuftsin is the four-residue immunopeptide Thr-Lys-Pro-Arg, it degrades in serum within minutes, so Selank bolts a Pro-Gly-Pro tail onto its C-terminus to extend the parent fragment into a more stable heptapeptide. It is therefore a synthetic analogue of tuftsin, a fragment of the immunoglobulin G heavy chain. Its molecular formula is C33H57N11O9, average molecular weight approximately 751.9 g/mol, CAS 129954-34-3, PubChem CID 11765600. Note the formula has no sulphur: Selank carries no methionine and none of Semax's oxidation liability. The identity record and study designs are in the Selank research monograph.
| Property | Semax | Selank |
|---|---|---|
| Amino-acid sequence | Met-Glu-His-Phe-Pro-Gly-Pro | Thr-Lys-Pro-Arg-Pro-Gly-Pro (TKPRPGP) |
| Parent peptide | ACTH(4-10) fragment (melanocortin family) | Tuftsin (Thr-Lys-Pro-Arg), an immunopeptide |
| Development code | None in common use (synonym MEHFPGP) | TP-7 |
| Molecular formula | C37H51N9O10S | C33H57N11O9 |
| Molecular weight | 813.9 g/mol | Approximately 751.9 g/mol |
| CAS number | 80714-61-0 | 129954-34-3 |
| PubChem CID | 9811102 | 11765600 |
The shared C-terminal Pro-Gly-Pro is the only structural echo between them, and it is a stability motif rather than a family marker - the same trick appears across unrelated regulatory peptides. Read past that tail and the molecules diverge completely: a methionine-led melanocortin fragment on one side, a lysine-and-arginine-rich tuftsin fragment on the other. The formulae make the point cleanly. Semax carries sulphur and ten oxygens; Selank carries eleven nitrogens and no sulphur at all. These are not variants of one scaffold. They are two different molecules that happen to be the same length.
This is the whole comparison, so it is worth being precise about the two ancestries. Semax descends from adrenocorticotropic hormone (ACTH). The ACTH(4-10) region it models is the melanocortin core - the same stretch of sequence shared across the melanocortin peptides - which is why Semax is classified, by homology, within melanocortin-peptide pharmacology rather than by any downstream readout. Selank descends from tuftsin, which is not a melanocortin at all: tuftsin is a tetrapeptide released from the Fc region of immunoglobulin G and historically described in the immunopeptide literature. So the two compounds enter the catalogue through different doors - one through the melanocortin / ACTH lineage, one through the tuftsin / immunopeptide lineage - and any grouping of them together rests on shared geography and shared peptide length, not shared receptor biology. This is sequence-homology classification only: no melanocortin-receptor or tuftsin-receptor activity, and no associated effect, is asserted for either compound.
That distinction is why filing the two together as "the Russian peptides" is a convenience of origin and era, not a pharmacological category. The shorthand common in online marketing bundles two molecules by where and when they were made, then implies a shared class their lineages do not support. The honest grouping is by parent peptide: Semax with the melanocortin fragments, Selank with the tuftsin analogues. The most-cited side-by-side study captures exactly this framing - Slominsky et al. (Doklady Biological Sciences, 2017; PMID 28702721) examined both Semax and Selank in the same 6-hydroxydopamine rat model and, in its own methods, identifies Semax as an ACTH(4-10) analogue and Selank as an analogue of immunomodulatory tuftsin. The study is referenced here for its design and the lineage labels it used, not for any result; no effect of either compound is asserted.
The two literatures barely overlap, which is itself informative. Each entry below is described strictly by what the study set out to measure; no result, effect size or benefit is asserted or implied. Endpoint selection reflects what the lineage literature happens to have measured, not a claimed area of action for either compound.
The two peptides sit at the same three levels, and the levels are not equal. Well-established: the chemistry. The sequences, the molecular formulae, the masses and the PubChem records are settled and independently checkable - Semax is C37H51N9O10S at 813.9 g/mol (CID 9811102), Selank is C33H57N11O9 at roughly 751.9 g/mol (CID 11765600), and their parent peptides (ACTH(4-10) and tuftsin) are documented lineage facts. None of that is in dispute.
The middle ground: the mechanism and animal literature, which is where most of the published work sits. These are in-vitro assays and rodent models measuring named endpoints - gene-expression patterns, neurotrophic content, behavioural readouts. A cultured cell and a model rat are not a person, and an endpoint that was measured is not an outcome that was shown. A good deal of the Selank and Semax literature is also Soviet-era and Russian-language, which makes independent replication harder to weigh from the outside.
The weakest part: human evidence. It is thin for both compounds and effectively absent at the standard a regulator would require. Neither Semax nor Selank is a licensed medicine, and neither has been shown to produce defined outcomes in humans.
Both ship as lyophilised (freeze-dried) powder for laboratory reconstitution in an appropriate laboratory solvent. This is bench handling of a reagent, not a preparation method for any use in humans or animals. The one place the two diverge as chemistry is oxidation: Semax carries an N-terminal methionine and that sulphur is oxidation-prone, whereas Selank has no methionine and no equivalent liability. Both are held desiccated and cold - longer-term at -20 C or colder for the freeze-dried solid, short-term at 2 to 8 C, with reconstituted solutions refrigerated and protected from light.
Peptide identity and purity should be verifiable rather than assumed: a vial that says one thing is not the same as a vial that is one thing. That gap is what a certificate of analysis closes - every Kovalabs batch ships with one, so the mass of the material in hand can be checked against the documented formula (C37H51N9O10S for Semax, C33H57N11O9 for Selank) rather than taken on trust.
Semax and Selank are supplied by Kovalabs for laboratory and in-vitro research only. They are not medicines, not supplements, and not for human or veterinary use, and nothing on this page describes a dose, a route, a schedule or an outcome. Both are research compounds that have not been evaluated by the MHRA or any comparable regulator for safety or efficacy in humans or animals. Every batch is third-party tested with a certificate of analysis. See the full research disclaimer for terms.
Their parent molecules. Semax (Met-Glu-His-Phe-Pro-Gly-Pro) is an analogue of the ACTH(4-10) fragment and sits in the melanocortin peptide family; Selank (Thr-Lys-Pro-Arg-Pro-Gly-Pro) is an analogue of tuftsin, an immunopeptide. They share a stabilising C-terminal Pro-Gly-Pro tail and a common originating laboratory, but their backbones, formulae (C37H51N9O10S versus C33H57N11O9) and lineages are distinct.
No. Grouping them as "the Russian peptides" reflects shared origin and shared length, not shared pharmacology. By parent peptide, Semax belongs with the melanocortin / ACTH fragments and Selank belongs with the tuftsin analogues. The honest classification is by lineage, not by an implied shared category.
Semax, marginally. Semax has an average molecular weight of 813.9 g/mol (C37H51N9O10S, PubChem CID 9811102); Selank is approximately 751.9 g/mol (C33H57N11O9, PubChem CID 11765600). A certificate of analysis lets the mass of the material in hand be checked against these identifiers.
Because of the first residue. Semax begins with methionine, a sulphur-bearing amino acid, which is why its formula carries an S and why a Semax solution is oxidation-prone. Selank's sequence (threonine, lysine, arginine, then prolines and glycine) contains no methionine and no cysteine, so its formula has no sulphur and no equivalent oxidation handling concern.
No. Neither Semax nor Selank has been approved as a medicine by the MHRA or any comparable regulator. Kovalabs supplies both strictly as research reagents, not for human or veterinary use.