Why the Distinction Is Not Pedantry
A peptide catalog accumulates compounds that are not peptides. They end up there because the same laboratories buy them, for the same experiments — not because anyone is confused about the chemistry.
But the distinction has practical consequences. A small molecule may not dissolve in bacteriostatic water. It may be sold as a salt whose counter-ion ruins your molar calculation. It may have no sequence to confirm by mass spectrometry. Treating it like a peptide because it arrived in a peptide vial is how experiments quietly go wrong.
Three compounds in this catalog are routinely mis-filed. Here is what each one actually is.
SLU-PP-332: An Acylhydrazone, Not a Peptide
SLU-PP-332 is a synthetic acylhydrazone of 290.32 g/mol — 4-hydroxy-N'-[(E)-naphthalen-2-ylmethylidene]benzohydrazide, CAS 303760-60-3. It has no amino acids in it.
It is a pan-agonist at the three oestrogen-related receptors, with reported EC50 values around 98 nM at ERRα, 230 nM at ERRβ and 430 nM at ERRγ. ERRα-preferring, not ERRα-selective.
Two points of confusion are worth naming. First, the oestrogen-related receptors are not oestrogen receptors. They are orphan nuclear receptors — structurally related, constitutively active, and unresponsive to oestradiol. One major supplier files SLU-PP-332 under "estrogen/progestogen receptor agonist" and another lists it as an inhibitor; both contradict the reported pharmacology.
Second, the "exercise mimetic" description is an argument from transcriptional overlap. ERRα drives a mitochondrial-biogenesis programme that overlaps with the PGC-1α response to endurance exercise. That is a real overlap. It is not a demonstration that the compound substitutes for training, and the supporting endurance data are mouse data.
It requires DMSO. It is lipophilic and will not dissolve in bacteriostatic water.
5-Amino-1MQ: A Quaternary Ammonium Salt
5-Amino-1MQ is a methylated quinolinium compound — also not a peptide — and a substrate-site-directed inhibitor of nicotinamide N-methyltransferase, with a reported IC50 around 1.2 µM.
The identifier situation is the thing to get right. The certificate identifies the free cation: CAS 685079-15-6, C10H11N2+, 159.21 g/mol. The iodide salt is separately catalogued at 286.11 g/mol, sometimes under CAS 42464-96-0.
About 1.89 mg of the iodide salt delivers 1 mg of the free cation. A molar concentration calculated from salt mass while assuming the cation is wrong by nearly a factor of two — which is more than enough to move a dose–response curve a long way.
It also needs DMSO, at roughly 2 mg/mL. Its connection to the NAD+ literature is covered in our piece on NAD+, NNMT and the salvage pathway.
ARA-290: A Peptide, Wrongly Filed as a Blend
The opposite error. ARA-290 — cibinetide — is a single 11-residue peptide, and several supplier catalogs file it under blends. It is not a blend of anything.
It is derived from the helix-B surface of erythropoietin, specifically the face that does not contact the EPO homodimeric receptor. That is the design: it is reported to activate the EPOR/CD131 heteroreceptor — the innate repair receptor — without activating EPOR homodimers, which separates erythropoietin's tissue-protective signalling from its effect on red-cell production.
Its identifier data is unusually inconsistent. Three molecular formulas circulate (C51H84N16O21, C51H82N16O20 and C52H91N17O21) alongside two CAS numbers (1208243-50-8 and 1239358-86-1), all paired with a mass near 1257 g/mol. Verify identity by mass spectrometry against your batch certificate rather than against a catalog.
The N-terminal residue is pyroglutamate, a cyclised glutamate. Listings writing the sequence as QEQLERALNSS have expanded it to glutamine; Pyr-EQLERALNSS is the same molecule.
Epithalon: A Peptide With an Evidence Problem
Epithalon is unambiguously a peptide — the tetrapeptide Ala-Glu-Asp-Gly, 390.35 g/mol, CAS 307297-39-8, the smallest in this catalog. The issue is not chemistry but provenance.
The great majority of its published literature — telomerase induction, telomere lengthening in cultured human cells, lifespan effects in rodents and Drosophila — originates from a single centre, the St. Petersburg Institute of Bioregulation and Gerontology, and has seen limited independent replication.
That is worth saying plainly because vendor marketing around this compound routinely does not. The material is what it says it is; the claims commonly attached to it are weaker than they are presented to be.
One structural caveat: at least one supplier data sheet describes an alternative γGlu–γAsp linkage that conflicts with the standard backbone. Check the structure on your certificate.
A Short Checklist
Before using anything from this group:
- Is it a peptide? SLU-PP-332 and 5-amino-1MQ are not. There is no sequence to confirm and no peptide-bond absorbance to measure at 214 nm in the usual way.
- What solvent? Both small molecules need DMSO. Keep the final concentration below your model system's tolerance.
- Salt or free form? It changes the molar calculation — by nearly twofold for 5-amino-1MQ.
- Which identifiers does the certificate give? Where catalogs disagree — and for ARA-290 and 5-amino-1MQ they disagree a lot — the certificate is the authority. Our COA verification hub has the batch records, and how to read a peptide COA explains what each test means.
Frequently Asked Questions
Is SLU-PP-332 a peptide?
No. It is a synthetic acylhydrazone of 290.32 g/mol with no amino acids. It is stocked alongside peptides because it appears in the same metabolic and mitochondrial research, and it requires a DMSO stock rather than bacteriostatic water.
Does SLU-PP-332 act on oestrogen receptors?
No. The oestrogen-related receptors are orphan nuclear receptors — related in structure but constitutively active and unresponsive to oestradiol. Supplier listings that file it under oestrogen-receptor agonists are wrong.
Is ARA-290 a blend?
No. It is a single 11-residue peptide derived from the helix-B surface of erythropoietin. Some catalogs file it under blends, which is a cataloguing error rather than a statement about the material.
Why does the 5-amino-1MQ mass differ between sources?
Because two forms are sold. The free cation is 159.21 g/mol; the iodide salt is 286.11. Roughly 1.89 mg of the salt delivers 1 mg of the cation, so the form you have determines your molar concentration.
References & Further Reading
Billon C et al., J Biol Chem 2023; Billon C et al., Nat Commun 2024; Neelakantan H et al., J Med Chem 2017;60:5015-5028; Brines M et al., Proc Natl Acad Sci USA 2008;105:10925-10930; Khavinson VKh et al., Bull Exp Biol Med 2003.