Semax: structure and analysis

What is Semax?

Semax is a synthetic heptapeptide based on the 4-7 fragment of adrenocorticotropic hormone, extended with a proline-glycine-proline tail. Seven residues in total: a four-residue active fragment plus a three-residue stabilising extension.

It shares its design logic with Selank — a short active sequence joined to a tail that slows enzymatic degradation — while deriving from an entirely different parent hormone.

The N-terminal residue of the ACTH(4-7) fragment is methionine, and that single fact drives most of what is analytically distinctive about this compound.

How is Semax produced?

Assembled by solid-phase peptide synthesis: the chain is built one residue at a time on an insoluble resin support, then cleaved from the resin, deprotected and purified — most commonly by reversed-phase high-performance liquid chromatography. The purified material is lyophilized to a dry solid.

The impurity profile that appears on a certificate is a record of where that process was imperfect: deletion sequences from an incomplete coupling, truncated chains, and species retaining a protecting group.

What are the molecular figures for Semax?

Calculated from the formula C37H51N9O10S, not measured. The average molecular weight counts the natural abundance of each element's isotopes; the monoisotopic mass is the mass of the single most abundant isotopic composition, which is the figure a mass spectrometer is usually compared against.

The expected ions follow from the monoisotopic mass by adding one proton per charge. They are a starting point for recognising a spectrum, not a substitute for one: adducts, salts, modifications and multiply charged species all move the observed m/z, and the certificate reports what was actually measured for a batch.

Adducts, salts, modifications and multiply charged species all move an observed m/z away from any figure calculated here, and a certificate reports what was measured for a batch rather than what was expected of it.

What is the sequence of Semax?

Semax is 7 residues long. Written in the one-letter amino-acid code, as the cited record states it:

The sequence is what an identity test resolves. The mass a spectrometer is compared against is the mass this chain implies, which is why a single missing or substituted residue changes the result by an amount that cannot be mistaken for instrument variation — the deletion is detectable rather than invisible.

Sequence information describes the molecule, not the material in a vial. What establishes a specific batch is the identity method and result on its certificate.

How does Semax compare with related compounds?

Related compounds are not interchangeable. Published figures differ between them, and in this catalogue three compounds share a GHRH backbone while several share the same structural class — which is exactly why identity is confirmed analytically rather than inferred from the label.

How is the identity of Semax confirmed?

Mass spectrometry confirms the seven-residue chain including the proline-glycine-proline extension. A truncated species lacking the tail is well separated in mass and readily identified.

Methionine oxidation is the modification an identity method will most often encounter here. The sulfoxide is sixteen mass units heavier than the parent, which is unambiguous at high resolution.

Which impurities can appear in Semax?

Methionine sulfoxide is the characteristic impurity for this compound, and its position at the N-terminus leaves it relatively exposed. A purity method for Semax needs to resolve the sulfoxide from the parent peptide, and a method that does not will report a purity figure that quietly includes it.

This is the clearest example in the catalogue of why a purity number needs its method attached. Two laboratories can analyse the same batch and report different figures depending on whether their gradient separates an oxidation product that differs from the target by a single oxygen atom.

The compound is otherwise chromatographically well behaved: seven residues is long enough for solid reversed-phase retention and short enough that deletion products remain resolvable.

What does a certificate of analysis for Semax report?

A certificate for a batch of this material names the batch, names the issuing laboratory, and states for each parameter both the method used and the specification the result was measured against. Identity and purity are the two core results; net peptide content states how much of the fill weight is actually peptide.

A certificate belongs to a batch, not to a product line. When a new batch is released it is tested again, and the certificate published against it is that batch's certificate — a previous batch's result is never carried forward.

Is Semax for human use?

No. This page describes structure and analysis. It makes no claim about what this compound does, and none should be inferred from it. Material is supplied for laboratory research use only: it is not a drug, food, dietary supplement, cosmetic or medical device, it is not for human or veterinary consumption, and no dosing, administration or reconstitution guidance is provided for any such use.

References

• ACTH (4-7), Pro-Gly-Pro (Semax) — PubChem, National Library of Medicine
• Pro-opiomelanocortin — human — UniProt Knowledgebase
• Stability of Semax acetyl to proteolysis in various biological media — Dokl Biol Sci, 2013