N-Acetyl Semax Amidate

1 Identity

Synthetic heptapeptide, N-terminally acetylated and C-terminally amidated. 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.

Sequence

Ac-Met-Glu-His-Phe-Pro-Gly-Pro-NH2 (Ac-MEHFPGP-NH2). Two modifications, both of which the product name implies: N-terminal acetylation and C-terminal amidation. Met-Glu-His-Phe is the ACTH(4-7) sequence; 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 rather than with the melanocortin receptor ligands despite its ACTH derivation. All residues proteinogenic and L-configured; no cysteine, no disulfide, no acylation beyond the terminal acetyl. Supplied lyophilized as the acetate or trifluoroacetate salt with the counterion declared. 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).

Molecular formula

C39H54N10O10S (free base, salt-free). Parent Semax C37H51N9O10S; acetylation +C2H2O; amidation replaces the terminal hydroxyl with an amine, -O +NH.

Average mass

854.981 Da for C39H54N10O10S on IUPAC 2021 abridged conventional atomic weights. Listings commonly print 855.0, and working laboratory tables commonly print 854.97; both are the same number to the precision each is quoted at, and 854.97 is what the pre-2021 table returns (854.972). Parent Semax 813.928 on the same table.

Monoisotopic mass

854.3745 Da neutral monoisotopic for C39H54N10O10S. [M+H]+ 855.3818; [M+2H]2+ 428.1945. Listings commonly print 854.375 and [M+H]+ 855.382, which agree to 0.001 Da. Parent Semax 813.3480 neutral / [M+H]+ 814.3552. The separation from the N-acetyl free acid at 855.3585 is exactly 0.9840 Da and the separation from the parent is exactly 41.0265.

Salt / variant note

Seven separable species. (1) This article, Ac-MEHFPGP-NH2, C39H54N10O10S, avg 854.981 / mono 854.3745, [M+H]+ 855.3818. (2) N-acetyl Semax free acid, Ac-MEHFPGP-OH, C39H53N9O11S, avg 855.965 / mono 855.3585, [M+H]+ 856.3658 - exactly +0.9840 Da, a separate catalog record, and the single likeliest wrong molecule to pass a nominal-mass identity test here. Note the trap in the numbers themselves: this article's [M+H]+ 855.3818 and the free acid's neutral monoisotopic 855.3585 differ by 0.023 Da, so a certificate reading '855' with no ion stated is uninterpretable. (3) Parent Semax, H-MEHFPGP-OH, C37H51N9O10S, avg 813.928 / mono 813.3480 - 41.03 Da lighter, separately listed at a lower price, so substitution is economic rather than accidental. (4) Semax sodium adduct at m/z 836.337, a real and commonly observed ion and the likeliest origin of the '840 Da' figure that circulates in this market; there is no species in this family at 840. (5) Semax C-terminal amide, C37H52N10O9S, avg 812.944 / mono 812.3639. (6) Methionine sulfoxide of this article, C39H54N10O11S, avg 870.980 / mono 870.3694, +15.9949, with the sulfone at +31.9898; oxidation is the dominant degradation route. (7) Adamax, Ada-MEHFPGP-OH, C48H65N9O11S, avg 976.160 / mono 975.4524, and the extended non-adamantyl variant Ac-MEHFPGP-Ala-Gly-OH, C44H61N11O13S, avg 984.096 / mono 983.4171, both of which trade under the Adamax name. Salt form is a further axis: acetate or trifluoroacetate shifts gravimetric weight without shifting the free-base mass.

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 markedly thinner for this derivative. The parent's base is predominantly Russian-language: rodent behavioral and neurochemical studies 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 amidated derivative specifically, the published record comprises a small number of synthetic-chemistry, stability and animal pharmacokinetic reports; no controlled human trial was identified and no ClinicalTrials.gov registration under that identity was found as of 11 August 2026. The citation index page lists primary sources with DOIs or PMIDs and tags each by study type; it does not summarize conclusions and it does not extrapolate from the parent to the derivative, because two terminal modifications make a different molecule.

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 mandatory rather than customary: Met1 oxidation is the named degradation route and headspace oxygen is its driver, so vials are filled and closed under nitrogen and the fill record states it. Equilibrate the sealed vial to room temperature before opening; the solid is hygroscopic and the label carries a close-immediately-after-weighing instruction. Ships ambient with a labeled cumulative excursion allowance of 120 hours at or below 30 degrees C, gel packs at 2 to 8 degrees C beyond that, and a single-use temperature logger in every export carton. 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 applies the same distinction across this family, giving the methionine-free conjugates the longer provisional interval. 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 both the interval and the packaging requirement. Printed retest date on every vial, first-expiry-first-out enforced against it.