Semax is a synthetic heptapeptide built from a fragment of a larger natural sequence plus a short C-terminal extension. This article is an identity and analytical reference: sequence, mass, chromatographic behaviour and verification. It makes no claim about what the compound does and contains no preparation, handling or dosing guidance.
The sequence
Semax is Met-Glu-His-Phe-Pro-Gly-Pro (MEHFPGP), average free-base mass approximately 814 g/mol.
The first four residues, Met-Glu-His-Phe, correspond to the ACTH(4–7) fragment. The final three, Pro-Gly-Pro, are a synthetic extension — the same extension carried by Selank, which is built on the tuftsin tetrapeptide instead. The two compounds are frequently discussed together for that reason, but they are different sequences with different masses.
The methionine is the analytical story
Methionine is, with tryptophan, the most oxidation-prone residue in the standard set. Methionine sulfoxide is +16 Da and typically elutes earlier than the parent peptide because the oxidised side chain is more polar. On an 814 Da peptide that shift is easily resolvable by a competent mass method, and a well-run chromatogram will separate the oxidised form rather than integrate it into the main peak.
This is the specific thing to look for on a Semax certificate. If a supplier publishes a single integrated peak with no comment on oxidation state, they have not told you whether the +16 species is present, absent or hiding under the integration window. Ask.
Detection: this one has a chromophore
Semax contains phenylalanine and histidine. Phenylalanine is a weak ultraviolet chromophore — considerably weaker than tryptophan or tyrosine, but not nothing — so a trace at 254 nm or 257 nm can carry some information alongside the primary read at approximately 214 nm on the peptide bond. Most of the analytical weight still sits at 214.
Prolines and peak shape
Two of the seven residues are proline. As with any proline-containing peptide, the bond preceding each proline can adopt cis or trans conformations that interconvert slowly on the chromatographic timescale, which can broaden the peak or produce a shoulder. That is a conformational property of the compound rather than a contaminant, and it is distinguished from a genuine impurity by mass, not by peak shape.
Charge and counter-ion
Semax carries a histidine and a free glutamate, so its net charge is pH-dependent rather than fixed. Counter-ion binding is more modest than on a strongly basic peptide, but net peptide content and chromatographic purity are still two separate numbers and a certificate should report both, along with the counter-ion form.
What an analysis should show
Column chemistry and dimensions, mobile phase and gradient, detection wavelength or wavelengths, retention time, integrated peak area with a visible integration window, and a mass confirmation near 814 g/mol — ideally with a note on whether a +16 Da species was detected. Separately: net peptide content and the declared counter-ion form.
Confirming identity independently
Search public chemical databases on Met-Glu-His-Phe-Pro-Gly-Pro rather than on the trade name. Our product pages carry compound identity links that run those queries directly.
How Semax is supplied here
Semax 5mg is supplied as a lyophilised powder in a sealed vial, with an independent reverse-phase HPLC analysis published on the product page alongside net peptide content, counter-ion form and vial size. Vials carry no batch or lot numbers and are matched to their published test by crimp and cap colour.
Frequently asked questions
What is the amino acid sequence of Semax?
Met-Glu-His-Phe-Pro-Gly-Pro (MEHFPGP), a heptapeptide.
What molecular weight should the mass spectrum show?
Approximately 814 g/mol for the free base; higher as a salt.
What is the relationship between Semax and ACTH?
The first four residues correspond to the ACTH(4–7) fragment. Semax is a short synthetic peptide, not ACTH, and a certificate for one is not evidence about the other.
Is Semax the same as Selank?
No. Selank is Thr-Lys-Pro-Arg-Pro-Gly-Pro. Both carry the Pro-Gly-Pro extension, but the parent fragments and the masses differ.
What impurity should I look for on a Semax chromatogram?
The methionine sulfoxide form, at +16 Da, usually eluting earlier than the parent peak.
Research use only. All products supplied by Battle Born Peptides are laboratory reference materials for in-vitro research and analytical use by qualified professionals. They are not drugs, foods, dietary supplements, cosmetics or medical devices; they are not approved by the FDA or any other regulator for use in humans or animals; and they are not intended to diagnose, treat, cure, mitigate or prevent any disease, or to affect the structure or any function of the body of humans or animals. Nothing in this article is preparation, handling or dosing guidance. See our full research-use terms.