What Selank is
Selank is a synthetic peptide of seven amino acids: Thr-Lys-Pro-Arg-Pro-Gly-Pro. The first four residues are tuftsin, a tetrapeptide fragment of the Fc region of immunoglobulin G that was identified in the 1970s as a stimulator of phagocytosis. The C-terminal Pro-Gly-Pro was added, as in Semax, to protect the fragment from peptidases and extend its action [1]. The design came from the same Russian institutes that produced Semax, and the two are usually discussed together, but they derive from different parent peptides and have been studied for different effects: Semax for cognition and neuroprotection, Selank for anxiety-related behaviour.
The sequence is strongly basic, with a lysine and an arginine, and contains three prolines, which make it rigid and resistant to most proteases. It has no aromatic residues, no methionine and no cysteine. The research material is a white lyophilised powder.
| Identifier | Value |
|---|---|
| CAS number | 129954-34-3 |
| Sequence | Thr-Lys-Pro-Arg-Pro-Gly-Pro |
| Parent | Tuftsin (Thr-Lys-Pro-Arg) with C-terminal Pro-Gly-Pro |
| Molecular formula | C33H57N11O9 |
| Molecular weight | 751.9 g/mol (average) |
| Residues | 7 |
| Non-natural residues | None |
| Termini | Free amine, free acid |
| Appearance | White lyophilised powder |
| Catalogue sizes | 10 mg |
How the literature describes its mechanism
Selank has no identified receptor, and the published mechanism is a set of effects observed in animals and cell systems. Three lines of evidence recur.
The first concerns GABAergic transmission. Volkova and colleagues reported that Selank altered the expression of genes involved in GABAergic neurotransmission in the rat brain, with a pattern that overlapped that of the benzodiazepine-class reference compound used in the study, and proposed that this overlap explains the anxiolytic-like behavioural effects [2]. Binding studies from the same tradition reported that Selank modulates the affinity of GABA-A receptors for their ligands, though the data are indirect.
The second concerns enkephalins. Selank has been reported to inhibit enkephalin-degrading enzymes in serum, which would raise the levels of endogenous opioid peptides, and this was proposed as part of its mechanism in early work [1, 3].
The third concerns the immune system, which is the heritage of the tuftsin parent. Selank has been reported to alter the expression of cytokine and interferon genes and to affect the balance of T-helper cell subsets in animal and cell studies [3]. Whether this has any relation to its behavioural effects is unknown; it is more likely an inherited property of the tuftsin sequence.
For an in-vitro programme the realistic readouts are gene-expression changes in neuronal cultures, effects on enkephalin-degrading enzyme activity, and immune-cell assays of the tuftsin kind. A laboratory looking for a defined receptor assay will not find one for this compound.
The research record
The animal literature reports anxiolytic-like effects of Selank in standard rodent tests (elevated plus maze, open field, conditioned avoidance), together with effects on learning and on stress responses, from the early 2000s onward [4]. The gene-expression and enzyme papers cited above are the mechanistic core of that work.
The human literature consists of Russian clinical trials in generalised anxiety disorder and related conditions, reported by Zozulya and colleagues among others, which supported the registration of Selank as a medicine in Russia as a nasal solution [5]. As with Semax, these trials have not been replicated outside Russia and have not been assessed by the MHRA, the EMA or the FDA. A reader should treat the compound as having a preclinical record of moderate size and an unreviewed clinical one.
Regulatory status in the United Kingdom
Selank has no marketing authorisation in the UK or any country outside Russia and some neighbouring states, and is not a medicine here. It is not controlled under the Misuse of Drugs Act. Whether a peptide of this kind falls within the Psychoactive Substances Act 2016 has not been tested; the material is in any case supplied as a chemical for in-vitro laboratory use under the Terms of Sale, not for human or veterinary administration. Purchasers must be 18 or over and are responsible for compliance with the laws and institutional rules that apply to them. Our guide to the UK rules on research compounds sets this out in more detail.
Selank is not on the WADA Prohibited List by name.
Handling, storage and stability
Selank is supplied lyophilised, sealed under nitrogen in a glass vial with a rubber stopper and an aluminium crimp.
Sealed vial. Store at 2–8 °C for routine use and at −20 °C for longer storage. Protect from light and moisture; a small basic peptide is hygroscopic. Allow the vial to reach room temperature before opening.
Reconstitution. Selank dissolves immediately in water, bacteriostatic water and buffers. Add the solvent and swirl. The reconstitution calculator gives the volume for a target concentration.
Reconstituted solution. Selank is one of the more stable short peptides in the catalogue. The three prolines protect against proteases, there is no methionine to oxidise and no aromatic residue to photo-degrade, and the only slow degradation route is deamidation-type chemistry at the Gly-Pro bond, which is minor. Solutions keep at 2–8 °C for several weeks; aliquot and freeze at −20 °C for longer storage. Use bacteriostatic water for solutions that will be kept, since the peptide itself has no preservative action.
Surfaces. A strongly basic peptide adsorbs to glass and to anionic surfaces at low concentration; use low-binding plastic for nanomolar dilutions. The storage and stability guide covers short basic peptides.
What a sound certificate for Selank looks like
Every batch we release carries an independent certificate of analysis, transcribed on the product page and in the certificate register.
Purity by RP-HPLC. Reversed-phase HPLC on a C18 column with UV detection at 214 or 220 nm, reporting the main peak as a percentage of all integrated peaks. The peptide has no aromatic residues, so detection at 280 nm is uninformative and a certificate quoting purity at that wavelength should prompt questions. A very hydrophilic, basic peptide elutes early on C18, and a certificate for a good batch shows a single peak at 98% or above with the common impurities being deletion sequences missing a proline.
Identity by LC-MS. The average molecular weight is 751.9 Da and the monoisotopic mass is 751.4 Da. With two basic side chains and a free amine, the peptide readily takes two or three protons and usually appears as [M+2H]²⁺ at m/z 376.7 or [M+3H]³⁺ at m/z 251.5; the certificate should say which it reports.
Net peptide content. A peptide with three basic sites carries a large weight of trifluoroacetate, often 15–20% of the powder mass, so net peptide content matters more for Selank than for most compounds and should be reported where available.
Endotoxin. Where tested, a LAL result in endotoxin units per milligram.
Our guide to reading a certificate of analysis goes through a complete report line by line.
Related compounds
Semax is the sister compound, an ACTH fragment with the same Pro-Gly-Pro extension, studied for cognitive and neuroprotective rather than anxiolytic effects. Epithalon is another short synthetic peptide from the same research tradition. Thymosin alpha-1 shares Selank's immunological heritage, being an immunomodulatory peptide of thymic origin.
Frequently asked questions
What is tuftsin? A tetrapeptide, Thr-Lys-Pro-Arg, from the Fc region of IgG, which stimulates phagocytosis by neutrophils and macrophages. Selank is tuftsin with a three-residue tail.
How does Selank differ from Semax? Different parent peptides (tuftsin versus ACTH), different sequences, and different reported effects. They share the Pro-Gly-Pro design principle and a Russian origin.
Is Selank a licensed medicine? In Russia, yes, as a nasal solution. In the UK, no, and the research material supplied here is not a medicine.
Why does the certificate quote a doubly charged ion? The peptide has three basic sites and readily carries two or three charges in electrospray; m/z 376.7 corresponds to the intact peptide with two protons.
References
- Kolomin T, Shadrina M, Slominsky P, Limborska S, Myasoedov N. A new generation of drugs: synthetic peptides based on natural regulatory peptides. Neuroscience & Medicine. 2013;4(4):223–252. doi:10.4236/nm.2013.44035.
- Volkova A, Shadrina M, Kolomin T, et al. Selank administration affects the expression of some genes involved in GABAergic neurotransmission. Frontiers in Pharmacology. 2016;7:31. doi:10.3389/fphar.2016.00031.
- Vyunova TV, Andreeva L, Shevchenko K, Myasoedov N. Peptide-based anxiolytics: the molecular aspects of heptapeptide Selank biological activity. Protein & Peptide Letters. 2018;25(10):924–929. doi:10.2174/0929866525666180925144642.
- Kozlovskii II, Danchev ND. The optimizing action of the synthetic peptide Selank on a conditioned active avoidance reflex in rats. Neuroscience and Behavioral Physiology. 2003;33(7):639–643. doi:10.1023/A:1024444321191.
- Zozulya AA, Neznamov GG, Syunyakov TS, et al. Efficacy and possible mechanisms of action of a new peptide anxiolytic selank in the treatment of generalized anxiety disorders and neurasthenia. Zhurnal Nevrologii i Psikhiatrii imeni S.S. Korsakova. 2008;108(4):38–48. PMID 18454096.
This monograph summarises the published literature for laboratory researchers. It is not medical advice, and nothing on this site is for human or veterinary use.