N-Acetyl Semax Research, Specifications & Scientific Information

Introduction

N-Acetyl Semax is the heptapeptide Semax with an acetyl group capping its N-terminal amine. That is the whole of the chemical difference, and it is a small one to draw on paper. It is not a small one in the laboratory: the free N-terminal amine is the donor atom that anchors copper(II) to the parent peptide, and capping it changes the coordination chemistry, the redox behaviour of the resulting complex, and — in the one cell experiment where the two peptides were compared side by side — whether the peptide protects neuronal cells from copper toxicity at all ^[1].

This page exists because the acetylated molecule is sold and discussed under its own name, and because the literature usually attached to that name is not its own. Semax has a substantial Russian clinical and preclinical record spanning three decades. The acetylated analogue has two indexed papers. This page reports the two, states plainly that the rest belongs to a different molecule, and stops there.

What Is N-Acetyl Semax?

Semax is a synthetic heptapeptide, Met-Glu-His-Phe-Pro-Gly-Pro, built from the 4–7 fragment of adrenocorticotropic hormone and extended at the C-terminus with the tripeptide Pro-Gly-Pro ^[1]. N-Acetyl Semax is that sequence with an acetyl group on the methionine alpha-amino nitrogen.

A complication sits directly on top of that definition. Two different molecules travel under the name. The peer-reviewed chemistry describes Ac-Semax: acetylation at the N-terminus, nothing else. PubChem, asked for "N-acetyl semax", returns compound identifier 172638603 — a record that carries the acetyl group and a C-terminal carboxamide in place of the free proline carboxylate, and which is also listed there as N-acetyl semax amidate under CAS registry number 2920938-90-3. The formula and mass in the specification table below are PubChem's, so they describe the doubly modified peptide.

Neither molecule is an approved medicine. Semax itself holds a pharmaceutical registration in the Russian Federation; that registration is for the unmodified heptapeptide and does not extend to an acetylated analogue. Neither form has been approved by the U.S. Food and Drug Administration for any indication, and no study of an acetylated Semax is registered on ClinicalTrials.gov.

N-Acetyl Semax Specifications

Two names circulate for two different molecules, and the difference is not cosmetic. PubChem resolves the name N-acetyl semax to compound identifier 172638603, whose recorded structure carries BOTH an acetyl group on the N-terminal methionine amine AND a C-terminal carboxamide in place of the free proline carboxylate — the doubly modified peptide also listed there as N-acetyl semax amidate, CAS registry number 2920938-90-3. The only peer-reviewed chemistry on an acetylated Semax, by contrast, describes Ac-Semax: the N-terminally acetylated heptapeptide, with the C-terminus discussed as a carboxylate. The formula and mass above are PubChem's, and therefore describe the doubly modified molecule. Any figure on this page is a reference value; which of the two molecules a given lot actually contains is a question the certificate of analysis for that lot answers and the product name does not.

Values that a public register does not carry are shown as not publicly characterised rather than estimated. Identifiers are reference values; the certificate of analysis supplied with a laboratory order is the record for a given lot.

How Does N-Acetyl Semax Work?

No mechanism of action is established for this molecule.

That is not an evasion, and it is worth stating precisely what it means. The parent peptide's own mechanism is itself poorly resolved — no single receptor has been identified for Semax, and its reported activity is described through downstream neurotrophin signalling rather than through a characterised binding site. Whatever uncertainty attaches to the parent therefore attaches to the acetylated analogue as well, with an additional uncertainty on top: nothing has been published showing that the acetylated peptide engages the same pathways at all.

What has been characterised is one specific consequence of the modification, and it is chemical rather than pharmacological. It is set out in the section below.

N-Acetyl Semax Mechanism of Action

In vitro research

Copper(II) coordination. In the parent peptide, the free N-terminal amine is the anchoring donor for copper(II), and the principal complex formed at physiological pH has a four-nitrogen coordination sphere. Acetylation removes that donor. The principal acetylated complex at physiological pH is instead a distorted three-nitrogen-one-oxygen chromophore with a weak apical interaction from the methionine sulphur ^[1].

Redox consequences. The weaker ligand field shifts the formal redox potential of the acetylated complex to a more positive value than the corresponding complex of the unmodified peptide. The practical consequence reported is a reversal of behaviour: the complex of the amino-free parent is redox-stable and unreactive toward ascorbate, whereas the acetylated complex is not ^[1].

Cell-level consequence. In the SH-SY5Y neuroblastoma line, acetylation did not protect against copper(II)-induced toxicity. The authors read this as demonstrating the crucial role of the free N-terminal amine in that protection ^[1]. This is the single most consequential result on this page, because it is a direct comparison of the two peptides in the same system, and the modified one lost the property.

Zinc(II), by contrast, is largely indifferent to the modification. Both peptides formed zinc(II) complexes of comparable strength, and confocal imaging showed that acetylation did not affect zinc influx into the cells. The zinc that entered showed a punctate subcellular distribution in both cases ^[1].

Proteolytic stability. A 2013 report in Doklady Biological Sciences examined the stability of acetylated Semax toward proteolysis in various biological media ^[2]. The indexed record for that paper carries no abstract, so this page states that the study exists and what it set out to measure, and quotes no result from it.

Findings in this section were obtained in solution chemistry and in a cultured cell line. Nothing in them establishes anything about intact animals or about humans.

What Is N-Acetyl Semax Being Researched For?

The honest answer is that it is not the subject of a research programme of its own. The two indexed papers on the molecule were not asking what it does; they were asking what acetylation changes.

• Metal-ion coordination chemistry — copper(II) and zinc(II) speciation, redox potentials, and the cellular consequences of both, with the acetylated peptide included as the comparison against the parent rather than as the compound of interest ^[1].
• Proteolytic stability of a modified regulatory peptide — the question that motivates most N-terminal acetylation in peptide chemistry, since a capped amine is not a substrate for aminopeptidases ^[2].

Everything else commonly listed under this name — the stroke and cognitive work, the neurotrophin expression studies, the optic-nerve literature — was performed with the unmodified heptapeptide. That material is summarised on the Semax entry, where it belongs, and is not repeated here.

Current Research Status

Status as of September 22, 2026. This block is rendered from maintained fields, not from prose, so it cannot go stale in one place and stay current in another.

N-Acetyl Semax vs Related Compounds

The parent peptide

Semax is the unmodified heptapeptide Met-Glu-His-Phe-Pro-Gly-Pro. It carries a Russian Federation pharmaceutical registration and a literature of clinical and preclinical reports going back to the 1990s. None of that literature was generated with the acetylated molecule, and the one head-to-head comparison that exists found the two peptides behaving differently ^[1].

The amidated variant

Material sold as N-Acetyl Semax frequently corresponds to the doubly modified peptide, acetylated at the N-terminus and amidated at the C-terminus, which is the structure PubChem carries under compound identifier 172638603. A page that treats the two as interchangeable is describing one molecule and citing another.

The other acetylated bioregulator

N-Acetyl Selank stands in the same relation to Selank — a marketed acetylated variant of a Russian-registered peptide, with far less literature of its own than the parent. The evidentiary situation is the same in both cases and so is the correct reading of it.

Why acetylation is done at all

Capping an N-terminal amine removes the substrate feature that aminopeptidases recognise, which is the standard route to extending a short peptide's survival in plasma. It is a rational modification. A rational modification is a hypothesis about improvement, not a demonstration of it, and for this molecule the demonstration has not been published.

No comparison of effect between these compounds is made on this page.

Chemical & Molecular Characteristics

The peptide backbone is seven residues with two prolines in the C-terminal tripeptide, one methionine, one histidine, one phenylalanine and one glutamate. The modification chemistry is what distinguishes the molecule, and it has three practical consequences.

The capped amine is the whole point, and the whole problem. N-terminal acetylation is done to block aminopeptidase attack. In this particular sequence, that same amine is also the primary metal-anchoring donor, so a modification chosen for stability necessarily alters the molecule's metal-binding chemistry as a side effect ^[1]. The two properties cannot be separated by this route.

The methionine is an oxidation liability in either form. A methionine thioether oxidises readily to the sulphoxide, adding sixteen daltons and producing a species that is chromatographically distinct from the parent and often incompletely resolved from it. In the acetylated complex the same sulphur makes a weak apical contact with bound copper ^[1], so its oxidation state is not incidental to the molecule's coordination behaviour.

Mass alone does not distinguish the two circulating structures well. Acetylation adds 42 daltons; C-terminal amidation subtracts one. The acetyl-only peptide and the acetylated-and-amidated peptide therefore differ by a single dalton, which is resolvable by modern instrumentation but is not the kind of difference a headline "mass spectrometry confirmed" line on a certificate demonstrates on its own. Establishing which structure a lot contains is a question for the method, not for the name on the vial.

Recorded identifiers under the PubChem entry for the name are compound identifier 172638603, CAS registry number 2920938-90-3, molecular formula C39H54N10O10S and average mass 855.0 g/mol. No UNII code resolves for either acetylated form in the FDA/NCATS Global Substance Registration System, so that field is published as unknown rather than filled with the parent peptide's code.

Frequently Asked Questions

Scientific References

1. Magrì A, Tabbì G, Giuffrida A, et al.. Influence of the N-terminus acetylation of Semax, a synthetic analog of ACTH(4-10), on copper(II) and zinc(II) coordination and biological properties Journal of inorganic biochemistry; 2016. PMID 27586814 doi:10.1016/j.jinorgbio.2016.08.013
2. Shevchenko KV, Nagaev IY, Andreeva LA, et al.. Stability of Semax acetyl to proteolysis in various biological media Doklady biological sciences : proceedings of the Academy of Sciences of the USSR, Biological sciences sections; 2013. PMID 23652441 doi:10.1134/S0012496613020166

Every identifier above is resolved against PubMed, Crossref or ClinicalTrials.gov at build time, and the title returned by the register is compared with the title stored here. A page does not publish if a reference fails to resolve.

Research-Use Information

For in vitro research use only. This material is a laboratory reagent. It is not a drug, food, dietary supplement, or cosmetic and is not for human or veterinary use, including ingestion, injection, or any other administration. No information on this page describes or implies any effect in humans or animals. Sold only to researchers under our Terms of Sale.