Semax

Semax is a synthetic heptapeptide, Met-Glu-His-Phe-Pro-Gly-Pro, described in the literature as an analog of the adrenocorticotropic hormone fragment ACTH(4-10). It retains the N-terminal Met-Glu-His-Phe of that native fragment and substitutes its C-terminal Arg-Trp-Gly with Pro-Gly-Pro, a proline-glycine-proline motif drawn from the naturally occurring glyproline family.

That substitution is the design feature of interest. The native ACTH(4-10) fragment is cleaved rapidly by amino- and carboxypeptidases, whereas the proline-flanked C-terminus of Semax is a poor substrate for those enzymes, and the originating literature attributes its markedly longer persistence to that change rather than to any alteration in receptor affinity.

Neither the native fragment nor the analog carries the corticotropic activity of full-length ACTH, because the residues required for melanocortin receptor 2 activation and downstream steroidogenesis lie outside this region of the sequence. The peptide was developed and characterised largely within Russian research institutions, and a substantial portion of the primary literature is published in Russian.

Rodent studies form the core of the mechanistic literature. Reported endpoints include brain-derived neurotrophic factor and nerve growth factor messenger RNA levels in hippocampal tissue, along with changes in the expression of their receptors, following administration in animal models.

Additional reported lines of investigation include modulation of dopaminergic and serotonergic signalling and effects in rodent cerebral ischaemia models. The literature base is geographically concentrated and much of it predates modern reporting standards, which is a material consideration when weighing the strength of evidence for this compound relative to more widely replicated peptides.

Purity is established by reversed-phase HPLC and identity confirmed by mass spectrometry, reported per lot on the Certificate of Analysis. The N-terminal methionine is the principal analytical liability for this sequence: oxidation to methionine sulfoxide is the most commonly observed degradation product, adding 16 daltons and typically resolving as a distinct, earlier-eluting peak.

That peak is the one to look for on incoming lot documentation. Its presence at elevated levels indicates oxidative exposure during synthesis, purification or storage rather than a synthesis error, which means it can develop in correctly made material that has been handled poorly. It is also the reason headspace air and prolonged storage in solution matter more for this compound than for most heptapeptides.