Semax: Structure, Naming and Identification

Semax is a synthetic heptapeptide. Most of what is written about it concerns its reported activity; this article concerns the molecule itself: the sequence, the figures that identify it, and the variants that circulate under related names.

The molecule

Semax has the sequence Met-Glu-His-Phe-Pro-Gly-Pro, seven residues with both ends unmodified. Its molecular formula is C37H51N9O10S, its molecular weight is 813.92 and its CAS number is 80714-61-0.

Where the sequence comes from

The first four residues, Met-Glu-His-Phe, correspond to positions 4 to 7 of adrenocorticotropic hormone. The last three, Pro-Gly-Pro, are not part of the hormone; they were added in the design of the molecule. The material sold for research is chemically synthesized.

Variants under related names

Two modified forms are sold alongside the parent molecule: an N-acetylated form, usually listed as N-Acetyl Semax, and an N-acetylated, C-terminally amidated form, usually listed as N-Acetyl Semax Amidate. Acetylation adds about 42 Da and amidation lowers the mass by about 1 Da, so the three have different molecular weights: 813.92, about 856, and about 855. They are different substances, and a record for one does not describe the others.

A residue that oxidizes

Semax contains methionine, which oxidizes on exposure to air. The oxidized product is 16 Da heavier and elutes as a separate peak on HPLC. A small oxidation peak is a normal finding for a methionine-containing peptide; its size at the time of testing is part of what the purity figure reports, and storage sealed, cold and away from light is what limits its growth afterwards.

Confirming what is in a vial

A mass spectrometry value near 813.9 identifies the parent molecule. A value near 855 or 856 identifies one of the modified forms. The sequence and CAS number on the specification should agree with the observed mass.

What FLASK lists

The material listed as Semax on this site is the unmodified heptapeptide, CAS 80714-61-0.

Frequently asked questions

Is N-Acetyl Semax the same as Semax?

No. Acetylation adds about 42 Da and amidation lowers the mass by about 1 Da, so the three forms have different molecular weights and are different substances.

Why does a Semax certificate show a small oxidation peak?

Semax contains methionine, which oxidizes on exposure to air to a product 16 Da heavier that elutes as a separate peak.

Which form does FLASK list?

The unmodified heptapeptide, CAS 80714-61-0.