Selank’s identity, and two database numbers that point at other molecules

Published August 28, 2026 · Artemis Labs

Selank is a seven-residue peptide: Thr-Lys-Pro-Arg-Pro-Gly-Pro, molecular formula C33H57N11O9, molecular weight 751.9, CAS number 129954-34-3, PubChem CID 11765600. Those fields are verified and consistent across sources. Two other identifiers commonly published alongside them are not. The PubChem CID 11129257 that appears on many Selank listings — including, until this page was written, our own — resolves to 3-(4-methoxyphenyl)-2-phenylthiophene, a small molecule with no peptide bonds at all. The ChEMBL identifier CHEMBL2104794 resolves to a compound called salfluverine. Neither is Selank. This page exists because the correction is more useful published than performed quietly.

Key findings

• Correct, verified fields (PubChem, retrieved August 28, 2026): CID 11765600, sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro, C33H57N11O9, MW 751.9, monoisotopic mass 751.43407244, InChIKey JTDTXGMXNXBGBZ-YVHUGQOKSA-N, CAS 129954-34-3, UNII TS9JR8EP1G.
• CID 11129257 is not Selank. It is 3-(4-methoxyphenyl)-2-phenylthiophene: formula C17H14OS, molecular weight 266.4, InChIKey HPUARIHJLXYGLH-UHFFFAOYSA-N.
• CHEMBL2104794 is not Selank. It resolves to salfluverine, molecular weight 281.23 — a different class of molecule entirely.
• We publish no ChEMBL identifier for Selank, because no correct one could be verified on the day this page was written.

The molecule itself

Read left to right, Selank is threonine, lysine, proline, arginine, proline, glycine, proline.

The first four — Thr-Lys-Pro-Arg — are tuftsin, a natural peptide released from an antibody molecule that acts on immune cells. The last three — Pro-Gly-Pro — are an added tail. Prolines have an unusual ring structure that makes the chain rigid and awkward for the enzymes that trim peptides from their ends, which is why this particular tail appears on several Russian research peptides.

An independent Polish group states the construction plainly while describing a related analog: the heptapeptide “has a structure of tuftsin, to which three natural L-amino-acids Pro-Gly-Pro are attached.”

Tuftsin’s own record is worth checking against, because the two are frequently conflated: PubChem CID 156080, formula C21H40N8O6, molecular weight 500.6. Different formula, different weight, different molecule.

How the wrong identifiers behave when you check them

The check takes about a minute and anyone can run it. Query PubChem by name for “Selank” and it returns CID 11765600, with the peptide’s formula and weight. Query CID 11129257 directly and it returns a thiophene — a sulfur-containing ring compound with a molecular weight of 266.4, roughly a third of Selank’s.

The mismatch is not subtle once you look. It is invisible if you never look, which is the actual lesson. A wrong identifier is not like a wrong sentence; it does not read as wrong. It sits in a specification table looking exactly as authoritative as the correct fields beside it, and it propagates every time someone copies the table.

The same applies to the ChEMBL entry. CHEMBL2104794 returns salfluverine, with a molecular weight of 281.23 and a structure containing a trifluoromethyl group — again, not a peptide.

Our own product record carried both of these. The chemistry fields on that record — sequence, formula, molecular weight, CAS — were correct throughout. That pattern is the signature of a copy-paste error in a reference table rather than a misunderstanding of the compound, and it is a common failure mode in this industry precisely because those fields are rarely re-derived once written.

How to verify a peptide’s identity fields yourself

Three checks catch nearly everything.

Resolve the identifier, do not read it. Open the PubChem CID and confirm the formula and molecular weight match what the document claims. A CID is a link, and a link either resolves to your compound or it does not.

Check that the formula and the sequence agree. For a peptide, the molecular formula should be consistent with the residues listed. A seven-residue peptide with a formula containing sulfur, when none of its residues contains sulfur, is a document to distrust.

Prefer identifiers with an authority behind them. The CAS number and the UNII — the identifier the FDA uses for ingredients — are maintained registries. For Selank those are 129954-34-3 and TS9JR8EP1G respectively, both retrievable from PubChem’s synonym list.

What the research does not show

Correct identity fields say what a molecule is. They say nothing about what it does, and nothing on this page is evidence of any effect. What Selank has and has not been shown to do in humans is on our human trials page.

Nor does a correct database record tell you what is in any particular vial. That is an analytical question, answered by testing material rather than by reading a table, and no claim about our own material appears on this page.

Finally, one commonly published number about Selank is absent here deliberately. Descriptions of the compound often state that the Pro-Gly-Pro tail extends its half-life ten to a hundred times relative to tuftsin. We could not trace that figure to any source in the retrieved literature, so we do not repeat it. What the literature supports is the qualitative point: the tail was added for stability against enzymatic breakdown.

Frequently asked questions

What is the correct PubChem CID for Selank?

11765600. Querying PubChem by the name “Selank” returns that record, whose formula and weight match the peptide.

What is Selank’s molecular weight?

751.9, for formula C33H57N11O9. Its exact monoisotopic mass is 751.43407244.

Does Selank have a ChEMBL ID?

We do not publish one. The identifier commonly cited resolves to a different compound, and no correct alternative could be verified.

Why publish your own error instead of just fixing it?

Because the wrong identifier is not unique to us — it circulates across the category — and a page that shows the check is more useful to a researcher than a silent edit. The underlying record is being corrected as well.

References

1. PubChem Compound Summary, CID 11765600 (Selank). National Library of Medicine. Retrieved August 28, 2026. pubchem.ncbi.nlm.nih.gov/compound/11765600.
2. PubChem Compound Summary, CID 11129257. Retrieved August 28, 2026. pubchem.ncbi.nlm.nih.gov/compound/11129257.
3. PubChem Compound Summary, CID 156080 (Tuftsin). Retrieved August 28, 2026. pubchem.ncbi.nlm.nih.gov/compound/156080.
4. Czabak-Garbacz R, Cygan B, Wolański L, Kozlovsky I. Pharmacol Rep. 2006. PMID 16963804.
5. Rogozinskaya EY, Lyapina MG. Bull Exp Biol Med. 2017. PMID 29181670.

Methodology: every identifier on this page was resolved directly against PubChem’s programmatic interface on August 28, 2026, and the two incorrect identifiers were confirmed by retrieving the records they return.

All compounds sold by Artemis Labs are for laboratory research use only. Nothing on this page is medical advice, and no statement has been evaluated by the FDA.