Selank

Selank is a synthetic heptapeptide built by extending a naturally occurring tetrapeptide. Its construction — a short bioactive core with a proline-rich tail bolted on — is a recognisable and deliberate peptide-design strategy, and it is the most useful thing to understand about the molecule.

Identity and construction

Tuftsin is the naturally occurring tetrapeptide Thr-Lys-Pro-Arg, a fragment of the immunoglobulin G heavy chain. Selank is tuftsin with a C-terminal Pro-Gly-Pro extension.

That extension is not arbitrary. Pro-Gly-Pro is a well-known stabilising motif in peptide design: proline residues are poor substrates for most exopeptidases, and flanking a glycine with two prolines produces a C-terminus that is markedly resistant to carboxypeptidase trimming. The strategy is to take a short active sequence with a very short lifetime and protect it structurally without altering the core.

The result is a peptide of which three of seven residues are proline — an unusually high proportion that dominates its conformational behaviour.

Structure

Seven standard L-residues, linear, free N- and C-termini. No cyclisation, no disulfide, no D-amino acids, no non-natural residues. Highly polar: a threonine hydroxyl, a lysine amine and an arginine guanidinium make it freely water-soluble.

There is no tryptophan, tyrosine or phenylalanine in the sequence — no aromatic residue at all. This has a direct practical consequence discussed below.

Specification and characterisation

• No 280 nm detection. With no aromatic residues, UV detection at 280 nm is uninformative for this peptide. Purity must be assessed at 214 nm against the amide backbone. A certificate omitting a 280 nm channel for Selank is not cutting a corner — there is nothing to detect. Conversely, a certificate reporting a 280 nm purity figure for Selank warrants a question.
• Proline cis–trans isomerism. With three prolines, the peptide populates multiple slowly interconverting conformers in solution. On reverse-phase chromatography this can produce peak broadening or apparent shoulders that are not impurities — they are the same molecule in different proline conformations. Raising column temperature accelerates interconversion and sharpens the peak. This is a genuine and frequently misdiagnosed artefact for proline-rich peptides, and reading it as a purity failure is a common error.
• Mass confirmation against 751.87.
• Counter-ion and net peptide content. Two basic residues on a heptapeptide gives a meaningful counter-ion burden. Note the separate acetate registry number in the table.
• Water content by Karl Fischer.

Handling and stability

Store sealed at 2–8 °C, dry, protected from light. Equilibrate in a desiccator before opening.

Chemically this is one of the more robust peptides in the catalogue as a dry solid: no cysteine, no methionine, no tryptophan, no asparagine — which is to say none of the four residues that drive the common degradation routes described elsewhere in this library. Reference catalogues report solubility in PBS at pH 7.2 at 10 mg/mL.

Note that reference sources do not publish compound-specific light-sensitivity or hygroscopicity data for Selank. The storage guidance above is the general lyophilised-peptide practice rather than a compound-specific finding, and is stated as such.

Related compounds in this library

No close relative here. KPV and Epitalon are the other short, all-natural-residue, linear peptides in the catalogue, and all three share the same broad handling profile.

References

Chemical, specification and analytical sources. This list is deliberately limited to chemistry and analytical references.

• Cayman Chemical 27720, Selank — formula, molecular weight, sequence, salt form, solubility, purity
• MedChemExpress, Selank — target classification
• ChemicalBook, CAS 129954-34-3 — registry confirmation
• Bachem, Handling and Storage Guidelines for Peptides — general lyophilised peptide handling

Cosmic Aminos supplies this material as a laboratory reagent for in-vitro research use only. It is not a drug, food, cosmetic or dietary supplement, is not approved by the Food and Drug Administration for any use, and is not for human or veterinary consumption. No dosing, administration or preparation guidance is provided.