Semax: Molecular Characterization and Peptide Chemistry — A Research Reference

The sequence is methionine-glutamate-histidine-phenylalanine-proline-glycine-proline, written MEHFPGP, a heptapeptide of approximately 814 daltons.

The first four residues correspond to positions 4 through 7 of adrenocorticotropic hormone, the fragment conventionally written ACTH(4-7). The remaining three are the tripeptide proline-glycine-proline, which does not occur at that position in the parent and was appended.

The core-motif truncation

This is the structurally decisive point. The melanocortin peptides — alpha-MSH, ACTH and their relatives — share a four-residue core motif, histidine-phenylalanine-arginine-tryptophan, and it is that motif the melanocortin receptors engage. Structure-activity work on the corresponding tetrapeptide established which of the four positions tolerate substitution and which are required for receptor engagement, with the arginine and tryptophan positions proving substantially less tolerant of substitution [3]. Earlier work on synthetic analogues of the longer ACTH(4-10) core region had already established the sequence's activity profile [4].

Semax contains only the first two residues of that motif — the histidine and the phenylalanine — and stops there. The arginine and tryptophan are absent entirely. A molecule carrying half a recognition motif is not a ligand for the receptor that motif serves, and Semax is accordingly not characterized as a melanocortin agonist. Its ACTH lineage is a matter of sequence provenance rather than of shared pharmacology, and listings that group it with melanocortin analogues on the strength of the name are mistaken.

The appended cap

Proline is the one amino acid whose side chain closes back onto its own backbone nitrogen, and a proline on the amino side of a peptide bond makes that bond a poor substrate for most peptidases — enzymes that cleave ordinary chains stall at proline. Flanking a glycine with prolines caps the carboxyl terminus against exopeptidase attack while leaving the ACTH-derived fragment chemically untouched. The same construction appears in Selank, where a different natural tetrapeptide carries the identical cap.

The composition worth noting for handling is the methionine at position 1 — a sulphur-containing residue and the most oxidation-prone in the standard amino acid set.

No cell-surface receptor has been established for this peptide. Reported in-vitro and preparation-level work has examined effects on monoamine systems in isolated preparations [1] and on neurochemical measures in model systems [2], but a defined molecular target has not been identified, and the mechanistic picture remains correspondingly open.

Two limitations are worth stating plainly, because they affect what a reader can independently verify. Much of the primary work on this compound was published in Russian-language journals with limited international indexing, so the accessible record is thinner than for compounds of comparable age developed elsewhere. And the older literature predates routine screening for the synthesis-related impurities described below, so a preparation's actual composition in those studies was less certain than a modern certificate makes it.

The structural chemistry set out above is well established. The mechanism is not.

Mass spectrometry confirms the intact molecular mass near 814 daltons. For this sequence the measurement also reports on oxidation state: an oxidized methionine adds a defined sixteen-dalton increment, so a batch carrying the sulfoxide shows a satellite mass above the target. Its absence is part of what a clean identity result asserts. An N-acetylated variant also circulates and differs by a defined 42 daltons, so the stated theoretical mass identifies which construct a batch is.

Reversed-phase HPLC resolves the main peak from related substances and yields the purity figure. A seven-residue synthesis produces few deletion sequences, so the profile is usually simple; the compound-specific related substance is the methionine sulfoxide, which separates from the unoxidized peptide and typically elutes close to the main peak. Proline-containing chains can additionally present as slowly interconverting conformers, appearing as broadened or split peaks rather than as genuine impurities — a distinction the chromatogram answers and a headline percentage does not.

One detail follows from composition: the single phenylalanine gives only weak absorbance at 280 nanometres, so quantitation generally relies on backbone absorbance near 214 nanometres instead.

Net peptide content accounts for counter-ions and residual water, determining how much peptide a nominal milligram figure represents.

Sealed lyophilized material is stable at ambient temperature for the duration of transit and requires no cold chain in shipping. On receipt, vials are refrigerated and kept out of direct light.

Reconstituted material is held refrigerated and used within the window the receiving facility's protocols specify, and repeated freeze-thaw cycling is avoided.

The methionine governs storage discipline. Oxidation to the sulfoxide proceeds in solution in the presence of dissolved oxygen and is accelerated by trace metals, so keeping the material dry until needed, limiting how often the vial is opened, and making solutions up fresh all matter more here than for a sequence without a sulphur-containing residue. The proline capping that resists enzymatic cleavage in biological media confers no advantage at all against this route.

A seven-residue chain with two prolines is otherwise conformationally stiff, presents very little surface for aggregation, and dissolves readily without mechanical assistance.

Semax is an investigational compound. It has not been approved by the FDA or any other regulatory authority, and no manufacturing, labeling, or quality standards for an approved product apply to it. Research material is sold strictly for laboratory research use; it must not be administered to humans or animals. Researchers are responsible for compliance with all institutional and jurisdictional requirements governing research chemicals.

Each batch of research-grade Semax is accompanied by an independent certificate of analysis specific to that lot.

Semax is a heptapeptide of approximately 814 daltons: the ACTH(4-7) fragment methionine-glutamate-histidine-phenylalanine followed by an appended proline-glycine-proline cap that resists exopeptidase attack. It carries only the first two residues of the four-residue melanocortin core motif, and is accordingly not a melanocortin receptor ligand despite its ACTH ancestry. No molecular target has been established for it, and much of its primary literature sits outside international indexing. Analytical verification rests on mass confirmation without a methionine sulfoxide satellite, careful reading of a proline-containing chromatogram, detection at 214 rather than 280 nanometres, and batch-specific net peptide content.