N-Acetyl Semax

1 Identity

Synthetic heptapeptide, N-terminally acetylated, C-terminal free acid. Linear, all-L, all proteinogenic; no cysteine, no disulfide, no lipid, no PEG, no metal, no acylation beyond the terminal acetyl. One methionine, which governs the stability specification. The parent is Semax, H-Met-Glu-His-Phe-Pro-Gly-Pro-OH (MEHFPGP). Not a synonym for N-Acetyl Semax Amidate (Ac-MEHFPGP-NH2), which is a separate catalog record 0.984 Da lighter, and emphatically not a synonym for Adamax, the adamantane-modified conjugate, which is a separate record and a different molecule. This last confusion is not hypothetical on this shelf: it is the subject of the company's own documented case study.

Sequence

Ac-Met-Glu-His-Phe-Pro-Gly-Pro-OH (Ac-MEHFPGP-OH). Seven proteinogenic L-residues; free C-terminal carboxylic acid, not amidated. Met-Glu-His-Phe is the ACTH(4-7) sequence and Pro-Gly-Pro is a synthetic C-terminal extension. The sequence stops short of the His-Phe-Arg-Trp melanocortin core message, which is why the compound is classed with the neuroactive regulatory peptides and not with the melanocortin receptor ligands despite its ACTH derivation. The N-terminal alpha-amine is capped; the His3 imidazole and the Glu2 carboxylate remain free. Methionine at position 1 is the analytically decisive feature: it oxidizes to the sulfoxide (+15.9949 Da) and, more slowly, to the sulfone (+31.9898 Da). Two prolines produce cis/trans conformer broadening, which is a method-development problem rather than an impurity.

Molecular formula

C39H53N9O11S (free acid, free base, salt-free). Parent Semax C37H51N9O10S; N-terminal acetylation is exactly +C2H2O.

Average mass

855.965 Da for C39H53N9O11S on IUPAC 2021 abridged conventional atomic weights. Parent Semax 813.928 average on the same table. The acetyl increment is +42.037 average.

Monoisotopic mass

855.3585 Da neutral monoisotopic for C39H53N9O11S. [M+H]+ 856.3658; [M+2H]2+ 428.6865. Parent Semax 813.3480 neutral / [M+H]+ 814.3552. The acetyl increment is exactly +42.0106 monoisotopic, and the separation from the amidate at 854.3745 is exactly 0.9840.

Salt / variant note

This name sits at the center of the most consequential substitution documented anywhere in this catalog, and the arithmetic is the whole defense. (1) Parent Semax, H-MEHFPGP-OH, C37H51N9O10S, avg 813.928 / mono 813.3480, [M+H]+ 814.3552 - 42.011 Da lighter and the cheapest substitution. (2) Semax sodium adduct, observed at m/z 836.337: a real and commonly seen ion, and the likeliest origin of the '840 Da' figure that circulates in this market. There is no species in this family at 840. (3) N-Acetyl Semax Amidate, Ac-MEHFPGP-NH2, C39H54N10O10S, avg 854.981 / mono 854.3745, [M+H]+ 855.3818 - exactly 0.9840 Da below this article, invisible on a unit-resolution quadrupole, separately cataloged, and the form this channel more often actually ships. (4) Semax C-terminal amide, C37H52N10O9S, avg 812.944 / mono 812.3639. (5) Methionine sulfoxide of this article, C39H53N9O12S, +15.9949, and the sulfone at +31.9898; because Met1 is the N-terminal residue and is capped, oxidation is the dominant degradation route and carries its own numeric limit. (6) Adamax, Ada-MEHFPGP-OH, C48H65N9O11S, avg 976.160 / mono 975.4524, [M+H]+ 976.4597 - 162.104 Da heavier than the parent. (7) The extended non-adamantyl variant Ac-MEHFPGP-Ala-Gly-OH, C44H61N11O13S, avg 984.096 / mono 983.4171, also sold under the Adamax name. Two molecular formulas circulate for the adamantane-modified conjugate, and the masses they compute to differ by about two daltons. Whichever of the two is intended, the pair cannot both be right, and no lot is released against either number until the formula and the mass are reconciled in writing by the supplier.

2 Class & testing panel

Form

Single article

Testing panel

P1 — panel definition

3 Primary sources & evidence

The index reports the design and provenance of the literature, not a conclusion about effect.

Published literature exists for the parent and is thin for this derivative. The parent's base is predominantly Russian-language, comprising rodent behavioral and neurochemical work together with a small number of clinical reports, most originating from or associated with the institute that developed the compound; independent replication outside that group is sparse, and no adequate and well-controlled trial to United States registrational standards was identified. For the N-acetylated free acid specifically, the published record consists of a small number of synthetic-chemistry, stability and animal pharmacokinetic reports; no controlled human trial of the acetylated free acid was identified, and no ClinicalTrials.gov registration under that identity was found as of 11 August 2026. The citation index page lists primary sources by DOI or PMID with study type tagged, does not summarize conclusions, and does not extrapolate from the parent to the derivative.

4 Storage & specification

Storage

White to off-white lyophilized powder, acetate or trifluoroacetate salt as declared, in Type I amber glass under nitrogen, stoppered and crimped. Store at -20 degrees C plus or minus 5 degrees C, desiccated over silica, protected from light. Inert headspace is not optional on this article: Met1 oxidation is the named degradation route and headspace oxygen is the driver, so vials are filled and closed under nitrogen and the fill record states it. Equilibrate the sealed vial to room temperature before opening. Ships with a labeled cumulative excursion allowance and a single-use temperature logger in every export carton; the excursion record travels with the lot. Not stored reconstituted; the vial label and the certificate both say so.

Shelf life

Provisional 18-month retest interval at -20 degrees C plus or minus 5 degrees C, desiccated, light-protected and under inert headspace, stated as provisional pending this company's own stability data. Eighteen rather than twenty-four because of the oxidation-labile methionine: the catalog's own convention on this family is that the methionine-free conjugate carries the longer provisional interval and the methionine-containing article carries the shorter one. The confirming study is an ICH Q1A(R2) design with methionine sulfoxide as the primary stability-indicating attribute, alongside total related substances, des-acetyl species and water, at 0, 3, 6, 9, 12 and 18 months at -20 degrees C with 2 to 8 degrees C and 25 degrees C / 60 percent RH arms. Extension to 24 or 36 months only on real-time data. The sulfoxide limit, not total assay, sets the interval and the packaging requirement. Printed retest date on every vial, first-expiry-first-out enforced against it.