What Semax is
Semax is a heptapeptide — seven residues — constructed as a fragment analogue. Its first four residues reproduce a short stretch of adrenocorticotropic hormone, positions four through seven of that molecule, and the remaining three are an appended tail that does not occur in the parent sequence at all.
Written in single-letter notation the sequence is MEHFPGP: methionine, glutamic acid, histidine, phenylalanine, then the added proline-glycine-proline tail. That tail is the whole design idea, and it is also the reason the molecule's analytical behaviour is what it is.
| Property | Value | Where it is confirmed |
|---|---|---|
| Residue count | 7 | Synthesis record |
| Sequence | MEHFPGP | Synthesis record; identity result |
| Parent fragment | ACTH positions 4-7 | Published literature |
| Appended tail | Pro-Gly-Pro | Synthesis record |
| Approximate mass | near 813 g/mol | Certificate of analysis |
| Physical form supplied | Lyophilized solid | Label and batch record |
Why the Pro-Gly-Pro tail is the point
Short peptides are cleaved quickly by exopeptidases — enzymes that trim residues from the ends of a chain. A four-residue fragment on its own is an easy target. The Pro-Gly-Pro tail is an established way of blunting that: proline's side chain loops back and bonds to its own backbone nitrogen, producing a rigid kink that many peptidases handle poorly. Appending it gives the enzymes a difficult end to work on.
That design choice has direct consequences for what a report shows:
- Proline couples less efficiently during synthesis. Two prolines in a seven-residue chain means deletion sequences are the most likely synthesis-related impurity, and because a chain missing one residue is chemically similar to the complete one, those peaks sit close to the main peak rather than far from it.
- The sequence begins with methionine. Methionine oxidises readily, and the oxidised species is 16 mass units heavier and more polar, so it elutes earlier. For this compound both failure modes are live: deletions adjacent to the main peak, oxidation on the early side of it.
- Seven residues is a short synthesis. Purity figures are typically high, which means a low one is informative rather than routine.
See how to read an HPLC chromatogram for where each of those appears on the plot.
Identity and purity on the report
The two results answer different questions and a report giving only one is incomplete. Purity comes from reversed-phase HPLC: everything reaching the detector is integrated, and the figure is the main peak's area as a percentage of the total. Identity comes either from mass agreement against the value calculated from the stated formula, or from retention-time matching against a reference standard run under the same method — reported as HPLC-RTM on a certificate.
For a fragment analogue, one check is worth making explicitly: the identity result should correspond to the seven-residue molecule, not the four-residue parent fragment. Those differ by the mass of the appended tail, a difference far beyond any method's tolerance. A compound defined by an addition should have documentation confirming the addition is present.
Storage of the lyophilized solid
Supplied as a freeze-dried solid, the material is governed by temperature, moisture, and — because of the N-terminal methionine — air. Cold storage slows the chemistry. The solid is hygroscopic, so a vial opened before it has equilibrated to room temperature will condense atmospheric water into it, and adsorbed water is what lets reactions proceed in what appears to be a dry powder. An intact seal is doing real work for an oxidation-susceptible sequence rather than being generic advice.
Stability is documented rather than assumed: a laboratory establishes it by holding material under defined conditions and re-analysing at intervals. Where a retest date is stated, the question worth asking is what data supports it. Storing lyophilized research materials covers the general case.
What the published literature covers
The published record is preclinical and, unusually for this category, substantially non-English — a large share of the early work appeared in Russian-language journals, where the compound was first described and most extensively studied. Reported areas of investigation include neuropeptide signalling, models of cerebral ischaemia, and behavioural studies in rodents.
Two characteristics of that literature are worth stating plainly. Concentration within a single research tradition means independent replication outside it is thinner than the total volume of publications would suggest. And regulatory status differs by jurisdiction: this compound is supplied for laboratory research only and has not completed the process that would establish safety or efficacy for any medical indication in the United States. Findings in rodent and cell-culture models do not transfer automatically to other species.
Arctic Lab Supply does not publish research conclusions, recommend applications, or provide guidance on experimental design.