What is the CAS number for Semax?

80714-61-0. PubChem CID 9811102 and UNII I5FAL2585H identify the same compound.

Why are there two PubChem entries?

One indexes the free peptide at 813.9 Da, the other the acetate salt at 874.0 Da. Synthetic material is commonly supplied as a salt.

Should purity be high for a peptide this short?

Generally yes. Seven residues is a short synthesis with fewer opportunities for truncation, so a low figure warrants scrutiny.

Semax (ACTH Fragment Peptide)

Semax CAS Number and Chemical Identity

JMWritten & reviewed by Jack Muncaster · Founder, UK PeptidesLast reviewed 2026-08-232 cited sources

Semax carries CAS Registry Number 80714-61-0, PubChem CID 9811102 and UNII I5FAL2585H, with molecular formula C37H51N9O10S and molecular weight 813.9 Da. The acetate salt is indexed separately as CID 155977617 at 874.0 Da, which is the form most synthetic material is supplied in.

Key facts

CAS Registry Number: 80714-61-0
PubChem CID (free peptide): 9811102
PubChem CID (acetate): 155977617
UNII: I5FAL2585H
Molecular formula: C37H51N9O10S
Molecular weight: 813.9 Da
Acetate salt weight: 874.0 Da

Why identifiers beat names

Semax appears in the literature and in supplier catalogues under several descriptions: Semax, ACTH(4-7)-PGP, ACTH(4-10) analogue, MEHFPGP, and the full systematic name. A CAS number, PubChem CID and UNII are unambiguous where those descriptions are not. When checking whether a certificate of analysis describes the compound a paper studied, compare identifiers rather than labels.

The salt form and the mass difference

PubChem indexes the free peptide at 813.9 Da and the acetate salt separately at 874.0 Da — a difference of roughly 60 Da, consistent with one acetate. This matters practically: a certificate reporting gross vial weight is not reporting net peptide content, and the two differ by the counter-ion. A certificate that states peptide content separately from gross weight is describing this correctly.

Research material referenced

Semax 10mg — third-party HPLC tested

View — £24.99

Confirming identity

Mass spectrometry against the theoretical mass for MEHFPGP is the identity check. Because there is a single methionine, an oxidised species appears at +16 Da; unlike peptides with two methionines, +32 is not expected and its presence would warrant explanation.

Confirming purity

Reverse-phase HPLC quantifies how much of the sample is the target peptide against truncated sequences, deletion sequences and oxidation products. For a seven-residue peptide, synthesis is short and comparatively clean, so purity figures are typically high — which makes an unexpectedly low figure, or a missing chromatogram, more informative than it would be for a longer sequence.

Extended research context

The Semax (ACTH Fragment Peptide) deep dive

Deep dive: what the Pro-Gly-Pro extension actually accomplishes

Semax is built from a four-residue fragment of ACTH with Pro-Gly-Pro appended, and that appendix does two separate jobs at once. Proline is the only proteinogenic amino acid whose side chain bonds back to its own backbone nitrogen, forming a ring that removes the amide hydrogen and locks rotation. Proteolytic enzymes generally need an extended, rotatable backbone at their active site, so bonds near proline are poor substrates for most of them — which is why proline-rich motifs recur throughout stabilised peptide design. The second job is subtractive: Pro-Gly-Pro occupies the positions where ACTH carries Arg-Trp-Gly, and those are the residues contributing to the parent hormone's adrenal-stimulating activity. One substitution therefore buys protease resistance and removes an unwanted pharmacology, which is unusually economical design.

Deep dive: the naming point worth getting right

Semax is near-universally described as an ACTH(4-10) analogue, and peer-reviewed paper titles use that phrase. Structurally it is not quite that. ACTH residues 4 to 10 are Met-Glu-His-Phe-Arg-Trp-Gly; Semax is Met-Glu-His-Phe-Pro-Gly-Pro. The first four residues match and the last three are wholly different — replacement rather than modification. PubChem, indexing by structure rather than design lineage, records it as ACTH(4-7) plus Pro-Gly-Pro. Neither name is wrong, but the loose one obscures the fact that the substituted segment is precisely the functionally consequential part.

Deep dive: reading an unevenly distributed evidence base

Semax's roughly 231 indexed records split along an unusual line. Mechanistic work — BDNF and trkB expression in rat hippocampus, transcriptomics in focal cerebral ischaemia, neurotrophin dynamics across brain regions — appears in international journals in English and can be assessed directly. Clinical work is concentrated in Russian-language publications, principally the Korsakov Journal of Neurology and Psychiatry, indexed by translated title and often without accessible English full text, much of it predating current standards for pre-registration and reporting. The honest position is that this is evidence which is difficult to verify independently, which is a different thing from evidence that is absent, and a different thing again from evidence that is established.

Research applications

▸Neurotrophin expression research (BDNF, NGF, TrkB, TrkA)
▸Neuroprotection and cerebral ischaemia models
▸Study of proline-stabilised peptide design
▸Comparative work on ACTH fragments without steroidogenic activity
▸Transcriptomic profiling in rodent brain models

Handling checklist

✓Store lyophilised material cold, dry and protected from light
✓Expect methionine oxidation as the degradation route (+16 Da; only one Met, so not +32)
✓No reducing agent needed — the sequence contains no cysteine
✓Introduce diluent gently against the vial wall; swirl rather than shake
✓Aliquot to avoid repeated freeze-thaw cycles
✓Check whether a certificate reports net peptide content or gross salt weight

Common research-handling mistakes

Learnt from thousands of researcher orders across our UK labs.

✗ Describing Semax as ACTH(4-10) without qualification

Fix: It shares only residues 4-7; Pro-Gly-Pro replaces Arg-Trp-Gly, and that replacement is the design's whole point.

✗ Treating Russian registration as equivalent to MHRA approval

Fix: Authorisations are jurisdictional and do not transfer. Semax has never been assessed by the MHRA, EMA or FDA.

✗ Reading a BDNF expression change as a demonstrated outcome

Fix: The studies measured gene and protein expression in rats. Expression is upstream of function and upstream again of any clinical claim.

✗ Assuming a named receptor exists

Fix: No primary receptor has been definitively established; the literature characterises downstream effects more confidently than the initiating event.

✗ Expecting ACTH-like adrenal effects

Fix: Semax does not stimulate adrenal steroidogenesis — the responsible residues were substituted out.

Continue researching

Peer-reviewed guides, comparators and matched reference materials.

Frequently asked questions

What is the CAS number for Semax?: 80714-61-0. PubChem CID 9811102 and UNII I5FAL2585H identify the same compound.
Why are there two PubChem entries?: One indexes the free peptide at 813.9 Da, the other the acetate salt at 874.0 Da. Synthetic material is commonly supplied as a salt.
Should purity be high for a peptide this short?: Generally yes. Seven residues is a short synthesis with fewer opportunities for truncation, so a low figure warrants scrutiny.

Primary sources & clinical trials

Peer-reviewed research and registered trials from PubMed, ClinicalTrials.gov, PubChem, FDA and NIH. All links open in a new tab and point to the primary source, so every claim can be verified at origin.

Written and reviewed by

Jack Muncaster · Founder, UK Peptides

Jack founded UK Peptides in Manchester after repeatedly receiving research compounds with missing or recycled paperwork. He is responsible for supplier selection, batch release decisions and the content published in this research library. Every article here is sourced to primary literature and every product page to a signed third-party certificate.

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