Selank is a synthetic heptapeptide built from a known immunopeptide fragment with a tripeptide extension. This article is an identity and analytical reference: sequence, mass, chromatographic behaviour and verification. It makes no claim about what the compound does and contains no preparation, handling or dosing guidance.
The sequence
Selank is Thr-Lys-Pro-Arg-Pro-Gly-Pro (TKPRPGP), average free-base mass approximately 752 g/mol.
The first four residues, Thr-Lys-Pro-Arg, are tuftsin, a naturally occurring immunoglobulin-derived tetrapeptide. The final three, Pro-Gly-Pro, are a C-terminal extension. That construction — a known short natural sequence plus a Pro-Gly-Pro tail — is the same design pattern used in Semax, which is an ACTH fragment carrying the same three-residue extension.
Three prolines in seven residues
Nearly half the sequence is proline, and that is the defining analytical fact about this compound.
Conformational broadening. Each bond preceding a proline can adopt cis or trans conformations that interconvert slowly relative to a chromatographic run. With three prolines, the number of accessible conformers is not small, and the practical result is peak broadening — sometimes a shoulder, occasionally something that looks like partial resolution of two species. It is one compound. Reading it as an impurity is the standard mistake on proline-rich peptides, and the way to settle it is mass confirmation across the peak rather than argument about peak shape.
Restricted backbone. Prolines constrain the backbone and reduce the conformational freedom that ordinarily lets a small peptide present a consistent hydrophobic face to a C18 surface. Retention is modest and method-sensitive.
Charge and detection
Selank carries a lysine and an arginine and no acidic residues, so it is strongly basic overall. Ion-pairing additive is load-bearing for retention, silanol interaction contributes tailing on silica-based columns, and counter-ion binding is significant — so net peptide content and chromatographic purity will differ meaningfully.
There is no aromatic residue in the sequence, so 280 nm detection is unavailable. The analysis must be read at approximately 214 nm on the peptide bond.
What an analysis should show
Column chemistry and dimensions, mobile phase and gradient with the ion-pairing additive named, detection wavelength, retention time, integrated peak area with a visible integration window, and mass confirmation near 752 g/mol. Separately: net peptide content and the declared counter-ion form. Where a peak is broad, a supplier who states whether they have confirmed mass consistency across the peak is telling you they read their own chromatogram.
Confirming identity independently
Search public chemical databases on Thr-Lys-Pro-Arg-Pro-Gly-Pro rather than on the trade name. Our product pages carry compound identity links that run those queries directly.
How Selank is supplied here
Selank 5mg is supplied as a lyophilised powder in a sealed vial, with an independent reverse-phase HPLC analysis published on the product page alongside net peptide content, counter-ion form and vial size. Vials carry no batch or lot numbers and are matched to their published test by crimp and cap colour.
Frequently asked questions
What is the sequence of Selank?
Thr-Lys-Pro-Arg-Pro-Gly-Pro (TKPRPGP), a heptapeptide.
What is the relationship between Selank and tuftsin?
The first four residues of Selank are the tuftsin sequence Thr-Lys-Pro-Arg. Selank adds a Pro-Gly-Pro extension at the C-terminus. They are different compounds.
What molecular weight should a mass spectrum show?
Approximately 752 g/mol for the free base; higher as a salt.
Is Selank the same as Semax?
No. Semax is Met-Glu-His-Phe-Pro-Gly-Pro, derived from an ACTH fragment. Both carry the same Pro-Gly-Pro extension, which is why they are often discussed together, but the parent fragments and the masses are different.
Why is my Selank peak broad?
Three prolines in seven residues produce cis–trans conformational broadening. It is a property of the molecule. Confirm by mass rather than by peak shape.
Research use only. All products supplied by Battle Born Peptides are laboratory reference materials for in-vitro research and analytical use by qualified professionals. They are not drugs, foods, dietary supplements, cosmetics or medical devices; they are not approved by the FDA or any other regulator for use in humans or animals; and they are not intended to diagnose, treat, cure, mitigate or prevent any disease, or to affect the structure or any function of the body of humans or animals. Nothing in this article is preparation, handling or dosing guidance. See our full research-use terms.