N-Acetyl Selank Amidate vs Selank: What Changes

N-acetyl Selank amidate is Selank with both termini capped: an acetyl group on the N-terminal amine and an amide replacing the C-terminal acid. The modifications target the enzymes that trim peptides from each end. Selank’s known degradation pattern in plasma makes that a sensible design, though published comparisons between the capped and unmodified forms are scarce.

For laboratory research use only. The compounds discussed are not approved for human or veterinary use and are not drugs, foods or cosmetics. This article summarises published research and is not medical advice.

Key points

Acetylation adds ~42 Da; amidation removes ~1 Da and the terminal negative charge.
Selank degrades from both ends in plasma, producing TKPRP, TKP, RP and GP.
Capping both termini addresses both routes simultaneously.
Selank is already a basic peptide; amidation makes it slightly more so.
No peer-reviewed head-to-head potency or pharmacokinetic data were found.

The forms compared

Form	Structure	Approx. mass	Termini
Selank	H-TKPRPGP-OH	751.9 g/mol	Free amine, free acid
N-acetyl Selank	Ac-TKPRPGP-OH	~793.9 g/mol	Capped amine, free acid
N-acetyl Selank amidate	Ac-TKPRPGP-NH₂	~792.9 g/mol	Capped amine, amide

Masses are calculated from Selank’s PubChem value plus 42.0 for acetylation and −1.0 for amidation. Our Selank research peptide is the unmodified form. Background: what is Selank?

Why both ends are capped

Zolotarev and colleagues followed the fate of tritium-labelled Selank in blood plasma and identified four major products: the pentapeptide TKPRP, the tripeptide TKP, and the dipeptides RP and GP (Zolotarev et al., 2006). The appearance of TKPRP implies loss of residues from the C-terminal end, while TKP points to further cleavage toward the N-terminal side. Because degradation proceeds from both directions, capping only one terminus would leave the other route open. That is the structural argument for the double-capped form.

Enzyme class	Requires	Blocked by
Aminopeptidases	Free N-terminal amine	N-acetylation
Carboxypeptidases	Free C-terminal carboxylate	C-terminal amidation
Endopeptidases	Internal bonds	Neither

The third row matters: capping does nothing about cleavage within the chain. Selank’s three prolines already provide some resistance to endopeptidases, since proline residues constrain the backbone, but internal cleavage is not eliminated.

A complication specific to Selank

Unlike many peptides, part of Selank’s described activity involves inhibiting enzymes rather than binding a receptor. In human plasma, Selank inhibited enkephalin-degrading carboxypeptidases and dicarboxypeptidases (Zolotarev et al., 2004). Inhibition of this kind depends on how the peptide fits the enzyme’s active site, and the free termini may contribute to that fit. Whether acetylation and amidation preserve, enhance or reduce this interaction has not, as far as we found, been measured. Similarly, the GABA-binding modulation described for Selank (Vyunova et al., 2018) has not been re-measured for the capped forms in published work.

What capping does not tell you

Chemical stabilisation is one of several recognised approaches to peptide stability, alongside pH and buffer optimisation and air exclusion (Nugrahadi et al., 2023). It changes how long a peptide survives, not necessarily how active it is. Three questions should be kept separate:

Chemical stability in the vial — affected mainly by temperature, moisture, light and pH, not by terminal capping.
Enzymatic stability in a biological matrix — the property capping is designed to improve.
Intrinsic activity — may increase, decrease or stay the same when termini are modified.

Identity testing

Supplier naming of these forms is inconsistent, so MS confirmation is the reliable check: a ~41–42 Da difference separates capped from uncapped material. Selank and Semax have both been identified in seized preparations by LC-MS/MS methods developed for this purpose (Vanhee et al., 2020), which confirms that routine analytical identification is practical.

Handling in the lab

Store powder at −20 °C, sealed and dark; solutions at 2–8 °C.
Neither form contains methionine or cysteine, so oxidation risk is lower than for Semax.
Both dissolve readily in water; see how to reconstitute peptides.
Concentrations: peptide reconstitution calculator.

Open questions

Do the capped forms retain Selank’s inhibitory effect on enkephalin-degrading enzymes?
How much longer do they survive in plasma under identical conditions?
Does the altered charge affect distribution or transport across membranes?

Related research

Frequently asked questions

What is N-acetyl Selank amidate?

It is Selank (Thr-Lys-Pro-Arg-Pro-Gly-Pro) with an acetyl group on the N-terminal amine and an amide at the C-terminus, two modifications intended to slow degradation by exopeptidases.

How does it differ from plain Selank?

Chemically, by about 42 Da of added acetyl and the loss of the C-terminal negative charge. Functionally, the capped termini are expected to resist aminopeptidases and carboxypeptidases that cleave the unmodified peptide.

Is NA-Selank the same thing?

Yes. ‘NA-Selank’ and ‘N-acetyl Selank’ refer to the same N-terminal modification; adding ‘amidate’ indicates the C-terminus is also capped.

Is the acetylated form stronger?

No peer-reviewed potency or pharmacokinetic comparison with Selank was found. The structural rationale is reasonable, but quantitative claims circulating online are not supported by data we could verify.

How do you tell the forms apart?

By mass spectrometry: Selank is about 751.9 g/mol, N-acetyl Selank about 793.9 g/mol and the amidated version about 792.9 g/mol.

References

Zolotarev IuA, et al. [Evenly tritium-labeled peptides and their in vivo and in vitro biodegradation]. Bioorg Khim. 2006. PMID: 16637290 https://pubmed.ncbi.nlm.nih.gov/16637290/
Vyunova TV, et al. Peptide-based Anxiolytics: The Molecular Aspects of Heptapeptide Selank Biological Activity. Protein Pept Lett. 2018. PMID: 30255741 https://pubmed.ncbi.nlm.nih.gov/30255741/
Zolotarev IuA, et al. [Leu-enkephalin homogeneously labeled with tritium in studying the Selank inhibiting effect on the enkephalin-degrading enzymes of human plasma]. Bioorg Khim. 2004. PMID: 15344652 https://pubmed.ncbi.nlm.nih.gov/15344652/
Nugrahadi PP, et al. Designing Formulation Strategies for Enhanced Stability of Therapeutic Peptides in Aqueous Solutions: A Review. Pharmaceutics. 2023. PMID: 36986796 https://pubmed.ncbi.nlm.nih.gov/36986796/
Vanhee C, et al. The occurrence of putative cognitive enhancing research peptides in seized pharmaceutical preparations: An incentive for controlling agencies to prepare for future encounters of the kind. Drug Test Anal. 2020. PMID: 31667971 https://pubmed.ncbi.nlm.nih.gov/31667971/
PubChem Compound Summary for CID 11765600, Selank. National Center for Biotechnology Information. https://pubchem.ncbi.nlm.nih.gov/compound/11765600