N-Acetyl semax amidate
N-acetyl semax, NA-Semax-amidate, NASA, Ac-MEHFPGP-NH2, acetyl semax amidate
N-Acetyl semax amidate is Semax with two chemical caps added: an acetyl group on the N-terminus and an amide on the C-terminus. Both modifications are standard medicinal-chemistry tactics for blocking exopeptidase attack. The critical fact about this compound is that, unlike Semax itself, it has essentially no peer-reviewed literature of its own, not even animal studies. Everything claimed for it is borrowed from Semax and asserted by sellers.
Mechanism
The chemistry is unambiguous and the rationale is sound in principle. Semax is destroyed in blood primarily by aminopeptidase cleavage of its N-terminal methionine, with carboxypeptidase attack at the other end. Acetylating the free alpha-amino group removes the positively charged N-terminus that aminopeptidases require, and converting the C-terminal carboxylate to a primary amide removes the free acid that carboxypeptidases recognise. Both caps should therefore extend the survival of the intact heptapeptide substantially. This is the same strategy used in numerous approved peptide drugs, and there is no reason to doubt it works chemically.
What does not follow is that the capped molecule retains Semax's pharmacology. Semax's direct receptor target has never been identified, so there is no binding assay against which to check whether acetylation and amidation preserve, reduce or abolish activity. Worse, a plausible reading of the Semax literature is that much of its in vivo effect is carried by its metabolite Pro-Gly-Pro, which is generated precisely by the degradation that these caps are designed to prevent. If that is right, blocking the metabolism could reduce rather than increase activity. Sellers present the acetylated amidated form as a straightforwardly "stronger, longer-lasting Semax". That claim has not been tested in any published experiment.
What the research shows
There is no meaningful published research on this molecule. The compound is a real, registered chemical entity. It carries a PubChem record and a CAS number, both of which were checked for this monograph and both of which match the formula C39H54N10O10S and a molar mass of 855.0 Da. What it does not have is a literature. PubMed searches carried out on 7 August 2026 for "N-acetyl semax", "acetyl semax amidate" and related terms returned no primary study of the molecule in any species; the handful of records that surface on loose keyword matching are about unrelated subjects. There are no pharmacokinetic data confirming that the caps actually extend half-life in vivo, no receptor-binding or functional comparison against Semax, no animal efficacy study, no toxicology, and no human data of any description.
This matters because the compound is marketed specifically on a potency claim, commonly presented as being several times stronger than Semax, or as having a dramatically longer duration. No experiment supporting any such ratio has been published. The honest position is that N-Acetyl semax amidate is a rationally designed analogue whose design logic is sound, whose actual properties are unmeasured, and whose entire evidence base consists of the assumption that it behaves like a parent compound that is itself only weakly evidenced. Two layers of extrapolation stacked on each other is not an evidence base. The three studies cited below all concern the parent peptide, Semax; none of them tested the acetylated amidated analogue, and they are listed only to make the design rationale traceable.
Evidence assessment
Preclinical only
Assigned the lowest tier as a formality. In truth even preclinical evidence is absent, since no published study of this specific molecule exists in any species, and all claims made for it are extrapolated from Semax.
Tiers are applied consistently across the library and re-checked when new trials read out. Read the grading method.
Key studies
N-terminal degradation of ACTH(4-10) and its synthetic analog semax by the rat blood enzymes Preclinical only
Establishes that Semax is degraded by N-terminal aminopeptidase attack, the basis for the design rationale behind acetylation, though the acetylated analogue itself was not studied.
Degradation of the ACTH(4-10) analog Semax in the presence of rat basal forebrain cell cultures and plasma membranes Preclinical only
Characterises the enzymatic breakdown pathway of Semax and the generation of shorter fragments, providing the mechanistic context for terminal-capping strategies.
Kinetics of Semax penetration into the brain and blood of rats after its intranasal administration Preclinical only
Shows rapid brain uptake and rapid blood clearance of the parent peptide, with Pro-Gly-Pro predominating among detectable species, relevant because the capped analogue is designed to suppress exactly this metabolism.
Safety
Unknown, in the fullest sense. No toxicology study, no adverse-event series, no human exposure data. It cannot be assumed to inherit Semax's benign-looking Russian clinical safety record: a longer-lived molecule with the same or altered receptor activity has a different exposure profile by definition, and blocked metabolism means blocked clearance of whatever activity it possesses. The material is produced by peptide synthesis houses for chemical supply, not under pharmaceutical GMP, and there is no independent verification of identity or purity in the products sold to consumers.
Regulatory status
| Jurisdiction | Status |
|---|---|
| United Kingdom | No UK marketing authorisation. Not a controlled drug, but as an unlicensed medicinal product it may not lawfully be sold, supplied or advertised for human use under the Human Medicines Regulations 2012. |
| United States | Not FDA-approved and not separately recognised in any FDA compounding determination. Regulatory attention to "Semax-related bulk drug substances" has concerned Semax free base and Semax acetate; the acetylated amidated analogue is a distinct chemical entity that has not been individually assessed. It is sold in the US only as an unapproved substance under a "research use only" label. |
| WADA (sport) | Not named on the WADA Prohibited List. As a non-approved pharmacological substance it would fall within the scope of WADA category S0, which prohibits substances lacking current regulatory approval for human therapeutic use. |
Questions
Nobody knows. That claim is a marketing inference from the chemistry, not a measured result. No published experiment has compared the two compounds on any endpoint: not binding, not brain exposure, not behaviour. Potency ratios quoted by sellers have no published source.
Chemically it should slow exopeptidase degradation, and that reasoning is sound. But no pharmacokinetic study of this molecule exists in any species, so the actual half-life is unmeasured. There is also a real possibility that blocking metabolism reduces activity, if Semax's effects depend partly on its Pro-Gly-Pro fragment.
None that test this molecule. It has a chemical identity (a PubChem entry and a CAS number, both of which check out), but a database registration is a catalogue fact, not a research finding. Searches of PubMed return no pharmacokinetic, pharmacodynamic, animal efficacy, toxicology or human study of the compound.
No such inference is available. A longer-lived molecule has a different exposure profile, and there is no toxicology, no human exposure data and no adverse-event record for this compound. Semax's Russian clinical safety record does not transfer to a chemically distinct analogue.
Because it is sold under a "research use only" label, which is largely a legal device rather than a description of intended use. That framing allows an unapproved compound to be supplied to consumers without meeting the evidentiary requirements that apply to medicines. It signals nothing about whether the compound has been studied.