Where to Buy Semax/Selank in 2026: Sizes, Purity Reports, Verification

Semax and Selank are two synthetic linear heptapeptides that share only a C-terminal Pro-Gly-Pro tripeptide, and each is also listed in an N-acetyl, C-terminally amidated form. Pepta Labs lists all four as 10 mg lyophilized powders in the neuropeptide category. This guide explains what separates the four listings chemically, and how they are supplied, verified and stored.

What Are Semax and Selank?

Semax is Met-Glu-His-Phe-Pro-Gly-Pro. Its first four residues are positions 4-7 of adrenocorticotropin, and Pro-Gly-Pro is appended at the C-terminus, hence the alias ACTH(4-7)-PGP. The methionine supplies the molecule's single sulfur atom. Selank is Thr-Lys-Pro-Arg-Pro-Gly-Pro: the tetrapeptide tuftsin followed by the same Pro-Gly-Pro extension. It contains no sulfur. Neither peptide is cyclic, neither contains cysteine, and both carry a free N-terminal amine and a free C-terminal carboxylic acid.

The N-Acetyl Amidate Forms

N-Acetyl Semax Amidate (Ac-Semax-NH2) and N-Acetyl Selank Amidate (Ac-Selank-NH2) keep the parent sequence intact and modify both ends: an acetyl group (CH3CO-) is attached to the N-terminal amine, and a primary amide (-NH2) replaces the C-terminal hydroxyl (-OH). Both changes are covalent, so the amidate forms are distinct chemical entities with their own formulas and masses.

The arithmetic is identical for both pairs. Acetylation adds C2H2O (+42.01 Da); amidation swaps -OH for -NH2 (-0.98 Da). The net change is +C2H3N, about +41.0 Da: Semax at 813.90 becomes 854.98, and Selank at 751.87 becomes 792.94. Pepta Labs states the formula and molecular weight for the two amidate listings but prints no CAS number for either, because no confirmed Chemical Abstracts registry number is assigned to them. Their identity therefore rests on the analytical report rather than on a registry entry.

How Pepta Labs Lists the Four Compounds

Each is a lyophilized powder in a sealed glass vial, 10 mg per vial, listed in the neuropeptide category. The 99.0% figure is the reversed-phase HPLC purity reported for the production run Pepta Labs sourced, with identity confirmed by mass spectrometry on the same run. Pepta Labs does not test in-house; the report comes from an independent laboratory commissioned through a cooperative purchasing group and is available by email request before you order. The salt form (TFA or acetate) is stated on the report. See our quality page for how reports are obtained.

How to Verify a Semax or Selank Listing

1. HPLC purity

The chromatogram reports the main peak as a percentage of all UV-absorbing peaks. 99.0% means the peptide fraction is 99.0% one species; it says nothing about water or counter-ion content, and on its own it cannot distinguish Semax from N-Acetyl Semax Amidate. See HPLC vs mass spectrometry.

2. Mass spectrometry: the 41 Da test

Mass spectrometry is the measurement that separates a parent from its acetylated amidated form. Compare the observed ions on the report with these theoretical values:

A vial sold as N-Acetyl Semax Amidate whose report shows [M+H]+ at 814.4 contains unmodified Semax. A shift of +42 with no accompanying -1 (m/z 856.4) would indicate acetylation without amidation. The expected-mass table lists these values alongside every other catalog compound.

3. Production-run report or lot-specific COA

A production-run report records the HPLC and MS results for the run a vendor sourced and is matched to the compound and quantity; a lot-specific COA is matched to a lot number on the vial. Pepta Labs provides production-run reports. The compound name, formula and observed mass should all belong to the listing you are buying. The COA verification guide walks through each section.

4. Registry numbers

CAS 80714-61-0 identifies free Semax and 129954-34-3 free Selank. Neither number applies to the amidate forms: a listing that reuses the parent CAS for an N-acetyl amidate product is mislabelled, and one that prints a CAS for an amidate should be able to say where the number comes from. See CAS numbers and molecular weights.

Storage and Shipping

• Shipped at ambient temperature as sealed lyophilized powders; the dry solids do not need a cold chain in transit.
• Refrigerate at 2-8 C on arrival; store at -20 C for the long term.
• Keep vials sealed and protected from light and moisture. Semax and its amidate contain methionine, which can oxidise to the sulfoxide (+16 Da) if left open to air, so reseal promptly.

The peptide storage guide covers handling in more detail.

US Regulatory Status

None of the four compounds carries an International Nonproprietary Name. Semax and Selank each have a UNII identifier (I5FAL2585H and TS9JR8EP1G), which records substance identity, not approval. Pepta Labs supplies all four as chemical reference materials for laboratory research, not as drugs. For how research peptides are regulated in the United States in 2026, see peptide legal status 2026.

Frequently Asked Questions

Are Semax and Selank related compounds?

Only through the shared C-terminal Pro-Gly-Pro. Their first four residues come from different parent sequences (ACTH 4-7 for Semax, tuftsin for Selank), and their formulas, masses and CAS numbers are different.

Why is there no CAS number for the amidate forms?

No confirmed Chemical Abstracts registry number is assigned to N-Acetyl Semax Amidate or N-Acetyl Selank Amidate, so Pepta Labs lists them by formula and molecular weight only. The parents are registered as CAS 80714-61-0 (Semax) and 129954-34-3 (Selank).

What does "amidate" mean on the label?

That the C-terminal carboxylic acid (-COOH) has been converted to a primary amide (-CONH2). Combined with the N-terminal acetyl group, this raises the molecular weight by about 41 Da relative to the parent peptide.

Which report figure should match the product page?

The RP-HPLC purity on the product page (99.0%) should match the purity on the report for the sourced production run, and the MS section should show an observed [M+H]+ matching the table above.

Where to Buy Semax and Selank

All products are supplied for laboratory research use only and are not for human or animal use.