Selank is a synthetic heptapeptide, a chain of seven amino acids, engineered as a stabilized analog of tuftsin, an immune-signaling peptide the body produces on its own. It was developed in Russia and studied mainly as an anxiolytic and nootropic compound, but it holds no FDA approval and is sold in Western markets only as a research chemical.
Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro, built by extending the endogenous immune peptide tuftsin with a stabilizing proline-glycine-proline tail.
Selank is a linear oligopeptide, a heptapeptide of seven L-amino acids joined head to tail, which sits well below the roughly fifty-residue threshold where a chain starts to be called a protein. The structure is a simple unbranched chain with no disulfide bridges or glycosylation, and its three proline residues lock the backbone into a compact, cleavage-resistant shape.
Selank has the molecular formula C33H57N11O9 and a molecular weight of approximately 751.9 grams per mole, placing it in the small-peptide range rather than the protein range.
Tuftsin is a naturally occurring tetrapeptide, Thr-Lys-Pro-Arg, that acts as an endogenous immunomodulator rather than a free-floating hormone. It is carried inside the Fc region of the immunoglobulin G heavy chain and becomes active only after enzymes cleave it loose, at which point it stimulates macrophages, monocytes, and neutrophils. Its practical flaw is instability: as a bare four-residue peptide it is broken down by peptidases within minutes.
Tuftsin is an endogenous tetrapeptide (Thr-Lys-Pro-Arg) cleaved from the Fc region of immunoglobulin G, and its rapid degradation by peptidases is the specific weakness Selank was engineered to overcome.
Selank's full sequence, Thr-Lys-Pro-Arg-Pro-Gly-Pro (single-letter TKPRPGP), splits cleanly into two functional halves. The first four residues are an exact copy of tuftsin and carry the inherited biological recognition motif; the final three, Pro-Gly-Pro, are the synthetic addition fused onto the carboxyl terminus to shield the bond most exposed to peptidase attack.
| Segment | Tuftsin core | Synthetic extension |
|---|---|---|
| Residues | Thr-Lys-Pro-Arg (first four) | Pro-Gly-Pro (last three) |
| Origin | Copied from endogenous tuftsin | Added by the designers |
| Role | Carries the active recognition motif | Protects the C-terminus from cleavage |
| Terminus | Amino (N) end | Carboxyl (C) end |
Selank's sequence is Thr-Lys-Pro-Arg-Pro-Gly-Pro, an exact tuftsin tetrapeptide joined at its carboxyl terminus to a synthetic proline-glycine-proline tripeptide.
Native tuftsin is degraded within minutes because peptidases readily cleave its exposed terminal bonds, so any effect disappears almost as fast as it appears. The proline-glycine-proline tail was added to fix exactly that: proline's ring-locked side chain resists most proteolytic enzymes, so capping the vulnerable carboxyl terminus builds an enzymatic roadblock that stretches the effective half-life from minutes to a far more usable window.
The proline-rich Pro-Gly-Pro extension was fused to the carboxyl terminus to block peptidase cleavage, lengthening Selank's half-life from tuftsin's few minutes while preserving the core recognition motif.
Selank came out of Russian peptide research, developed at the Institute of Molecular Genetics of the Russian Academy of Sciences together with the V. V. Zakusov Research Institute of Pharmacology. It sits in the same lineage that produced its better-known sibling Semax, a deliberate program aimed at turning naturally regulatory peptides into stable drugs for the nervous system.
Selank was developed at the Institute of Molecular Genetics of the Russian Academy of Sciences with the V. V. Zakusov Research Institute of Pharmacology, within the same Russian tradition that produced Semax.
Because Selank is a defined seven-residue sequence, it is built by chemical peptide synthesis rather than pulled from a biological source, most often by solid-phase synthesis that adds each amino acid stepwise to a resin-anchored chain. The finished material is a white lyophilized powder distributed in Western markets only under research-use labeling, not as an approved drug product.
Selank is manufactured by solid-phase peptide synthesis and supplied as a white lyophilized powder under research-use-only labeling in Western markets, with intranasal administration among the routes studied.
Selank's status splits sharply by jurisdiction, and that divergence is central to how the compound should be read. In the United States it carries no FDA approval for any use and is sold only as a research chemical labeled not for human consumption, while within Russia it has been studied in clinical trials and recognized as an anxiolytic agent, which is why most primary human evidence originates there.
Selank is not FDA-approved and is sold in the United States only as a research chemical labeled not for human consumption, though it has been clinically studied and recognized as an anxiolytic within the Russian pharmaceutical system.
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