Selank in Canada: Tuftsin, the PGP Tail and What to Test
Selank in Canada is usually ordered by labs studying short regulatory peptides, and it is one of the more deceptive compounds to assess from paperwork alone. The molecule is small, very polar and almost transparent to UV light at the wavelengths some labs report. A certificate can therefore look excellent while saying little. This guide explains where Selank’s sequence comes from, why its tail was added, and which analytical details a QC reviewer should check before a multi-vial lot is accepted into inventory.
Selank in Canada: the molecule behind the name
Selank is a synthetic heptapeptide, Thr-Lys-Pro-Arg-Pro-Gly-Pro, written TKPRPGP in one-letter code and occasionally listed as TP-7. Like Semax, it emerged from Russian peptide research. Its identity figures are the numbers every certificate should match:
| Property | Value |
|---|---|
| Sequence | Thr-Lys-Pro-Arg-Pro-Gly-Pro |
| Molecular formula | C33H57N11O9 |
| Average molecular weight | approx. 751.9 g/mol |
| CAS number | 129954-34-3 |
| Aromatic residues | None |
| Sulfur-containing residues | None |
The last two rows look like trivia. For analysis and storage, they turn out to be the most important lines in the table.
Tuftsin: the four-residue starting point
The first four residues of Selank, Thr-Lys-Pro-Arg, are tuftsin. Tuftsin is a naturally occurring tetrapeptide that is not made as a standalone peptide. It is cut out of a larger protein, the heavy chain of immunoglobulin G, by enzymatic cleavage, and it has been studied in the literature for decades as an immunomodulatory fragment acting on phagocytic cells in vitro.
A four-residue peptide has an obvious weakness: it is very short. Enzymes that nibble residues from the ends of peptides do not have far to go before nothing of the original sequence remains. That fragility is the problem Selank’s design addresses.
What the Pro-Gly-Pro tail changes
Selank is tuftsin with three residues added at the C-terminus: proline, glycine, proline. Proline is unusual among amino acids because its side chain bonds back onto the backbone nitrogen, forming a five-membered ring. The ring restricts the backbone’s flexibility and removes the amide hydrogen, which most peptidases need to position a bond for cleavage. A run of prolines at the end of a chain is therefore a practical shield against exopeptidase attack.
The same Pro-Gly-Pro extension appears on Semax, where it is attached to an ACTH fragment instead. The two peptides share a stabilisation strategy, not a parent. Our article on Semax and methionine oxidation covers that compound’s own quirks, and the Selank and Semax overview compares the pair.
A peptide with no chromophore
Scan the sequence for tryptophan, tyrosine or phenylalanine and you will find none. These aromatic side chains are what absorb UV light around 280 nm. Without them, Selank gives almost no signal at that wavelength, and neither do most impurities that could accompany it.
The consequence for anyone reading a certificate is straightforward:
- Purity for Selank should be measured in the 210 to 220 nm range, where the peptide bond absorbs and every peptide species is detected.
- A high purity figure reported at 280 nm on this compound reflects the choice of wavelength more than the quality of the material.
- The wavelength is usually printed on the chromatogram header. On Selank, it is the first thing to look for.
Retention and counter-ions in a basic, polar peptide
Selank has two strongly basic side chains, lysine and arginine, plus a free N-terminal amine, and almost no hydrophobic surface. On a reversed-phase column it is retained weakly and elutes early, sometimes near the solvent front where poorly retained impurities also collect. Methods that use an ion-pairing acid such as trifluoroacetic acid, and a shallow early gradient, give the main peak room to separate. A method that pushes Selank out with the void can make a sample look cleaner than it is. That is one of the ordinary reasons certificates of analysis can disagree.
Those same basic groups carry counter-ions in the solid. Peptides purified with trifluoroacetic acid are typically isolated as trifluoroacetate salts, and those exchanged afterwards often as acetate salts. For a small peptide with up to three positive charges, the counter-ion share of the weighed powder can be substantial. The arithmetic below is illustrative only, assuming one counter-ion per basic site and no water:
| Salt form (3 counter-ions) | Formula weight | Peptide share of mass |
|---|---|---|
| Trifluoroacetate | approx. 1094 | about 69% |
| Acetate | approx. 932 | about 81% |
Real material also holds residual water, and the actual counter-ion ratio varies, so the only reliable figure is a measured net peptide content. For labs planning experiments across many vials, that number matters more for Selank than for most larger peptides. The net peptide content article explains how it is determined.
Identity checks and deletion sequences
Mass spectrometry confirms Selank easily at about 751.9. It also catches the most likely synthesis errors: deletion sequences where a residue failed to couple. Losing one proline drops the mass by about 97 Da, losing the glycine by about 57 Da. Selank has three prolines, one in the tuftsin section and two in the tail, so a des-Pro variant could arise at any of three positions with an identical mass shift. Telling those apart takes chromatography or fragmentation data, not a single mass reading.
Keep the name straight as well. Tuftsin on its own is a separate substance with a different mass and registry number, not a shorter grade of Selank.
Storing and logging a Selank order
With no methionine, cysteine or tryptophan, Selank avoids the oxidation routes that trouble many peptides, and with no asparagine or glutamine it has no obvious deamidation site. The main enemy is moisture, since salt-form peptides readily absorb water from the air. For a multi-vial shipment:
- Check the certificate mass against 751.9 and confirm the detection wavelength.
- Match cap and crimp colours to the certificate and record the lot and vial count.
- Store unopened vials cold and dry, and warm each vial to room temperature before opening.
- Note the net peptide content, if reported, in your inventory so concentration calculations use it.
We stock Selank in 5mg and 10mg vials, shipped from within Canada, with mix-and-match volume pricing across the catalogue. Products are third-party tested for purity by HPLC, and certificates are published for some products on our certificates of analysis page.
Selank is sold by Bulk Peptides strictly for in-vitro laboratory research. It is not intended for human or animal use and is not a drug or health product.
