Semax vs N-Acetyl Semax Amidate: Structure and Naming Differences

Semax and N-acetyl Semax amidate share the same seven amino acids, Met-Glu-His-Phe-Pro-Gly-Pro, but are not the same compound. N-acetyl Semax amidate carries an acetyl group on the N-terminus and an amide in place of the free acid at the C-terminus. Those two end modifications raise the molecular weight from about 813.9 Da to about 855.0 Da and change how the molecule behaves in solution and in enzymatic assays.

What is Semax?

Semax is a heptapeptide built from the 4-7 fragment of adrenocorticotropic hormone, Met-Glu-His-Phe, extended with the tripeptide Pro-Gly-Pro. It was developed in Russia, where it is registered as a medicine, and most of its literature comes from Russian research groups, including studies of its effects on neurotrophin expression in rodent brain [1]. The Pro-Gly-Pro extension is associated with resistance to enzymatic breakdown, which has been studied directly [2].

What do the two modifications change?

N-terminal acetylation removes the positive charge of the free amine and blocks aminopeptidases that cleave from that end. C-terminal amidation removes the negative charge of the free carboxylate and blocks carboxypeptidases. Both are common strategies for extending the lifetime of short peptides in biological matrices.

How much published literature covers each form?

Semax has a peer-reviewed literature spanning several decades. N-acetyl Semax amidate appears mainly in supplier catalogs; peer-reviewed studies that name this exact form are scarce. Findings reported for Semax should not be assumed to transfer to the modified form without data on that form.

How can the two be told apart?

By mass. The calculated difference is about 41 Da, which any routine mass spectrometry identity test resolves. Supplier listings sometimes shorten the name to "NA-Semax", "N-Acetyl Semax" or simply "Semax", so the stated sequence notation, with or without the "Ac-" prefix and "-NH2" suffix, and the observed mass on the report are what identify the material.

Frequently asked questions

Is NA-Semax the same as N-acetyl Semax amidate?

In most catalogs, yes, although some listings use "N-acetyl Semax" for a form that is acetylated but not amidated. Only the stated structure and the observed mass settle the question.

Which form does FLASK list?

FLASK lists Semax (MEHFPGP, 813.9 Da, CAS 80714-61-0), the unmodified peptide.