What Is KPV? Identity, Purity, and How to Read the Certificate

KPV is three amino acids long. That sounds like it should make it the simplest compound in any catalog, and analytically it is close to the opposite. A tripeptide this short sits outside several assumptions that ordinary peptide documentation quietly relies on, and a KPV certificate that looks identical in format to a BPC-157 certificate is not telling you the same amount.

This is a documentation guide, not a research guide. It covers what the molecule is, what its certificate should say, and where the published literature actually stops.

What KPV is, chemically

KPV is Lys-Pro-Val: lysine, proline, valine. It is the C-terminal tripeptide of alpha-melanocyte-stimulating hormone, residues 11 to 13 of that 13-residue hormone, which is why you will see it written as alpha-MSH (11-13). The bracketed range is standard fragment notation rather than a brand convention, and the three-letter residue symbols are set by international nomenclature rules^[1]. The free base is C₁₆H₃₀N₄O₄ at 342.43 g/mol, CAS 67727-97-3.^[2] That formula is worth checking against the number on any certificate you are handed, because the two have to agree: summing standard atomic masses across C₁₆H₃₀N₄O₄ gives roughly 342.4, so a certificate quoting a materially different mass for a compound it calls KPV is describing something else, most often a salt form rather than the free base.

Because it is a fragment of a larger hormone rather than a compound designed from scratch, most of what circulates about KPV is inherited from the parent molecule rather than measured on the fragment itself. That distinction runs through everything below.

The distinction almost no catalog makes

In alpha-MSH itself, that terminal valine is amidated. It ends in Val-NH₂, not a free carboxyl group. The material sold under CAS 67727-97-3 is the free acid, which is a different molecule from the corresponding fragment as it exists inside the hormone.

This matters when you go to the literature, because the literature is not consistent either. Some published work uses the amide, H-KPV-NH₂. Some uses the free acid. If you are comparing two papers, or comparing your material against a paper, confirm which terminus each one used before you conclude anything about a discrepancy.

There is a second identity problem worth knowing about. Suppliers commonly print the same CAS number on both the free base and the acetate salt, which is chemically incorrect. The acetate is a different substance with a different molecular weight, in the region of 402 g/mol for a 1:1 salt. FDA raised exactly this point in its own 2026 review of KPV, describing the naming as not following established chemical nomenclature standards. If a certificate gives you a CAS number and a molecular weight that do not correspond to the same form, that is a documentation error, not a rounding difference.

You cannot read this one at 280 nm

KPV contains no tryptophan, no tyrosine and no phenylalanine. It has no aromatic residue at all, which means it has no chromophore at 280 nm.

The practical consequences are immediate. A280 is useless for determining concentration on this peptide. Detection has to be by peptide bond absorbance in the 210 to 220 nm range, and the published stability-indicating RP-HPLC method for KPV reads at 220 nm on a C18 column with a water and acetonitrile gradient, both with 0.1% TFA. If a KPV certificate reports a purity figure without stating the detection wavelength, you cannot tell whether the number came from an appropriate method.

What it degrades into

KPV has proline in position two. Peptides with proline in that position are prone to intramolecular cyclisation, and the characterised major degradant of KPV is the diketopiperazine, cyclo(Lys-Pro), confirmed under acid, alkaline and oxidative stress conditions.

That tells you what kind of liability this molecule has. It contains no cysteine, no methionine and no tryptophan, so it is not an oxidation-sensitive peptide in the way many others are. It is a hydrolysis and cyclisation liability. Handling and storage should be aimed at that failure mode, and a stability claim on a certificate is only meaningful if the method that produced it can separate the parent peak from the diketopiperazine.

Purity is not the same as how much peptide is in the vial

This applies to every peptide, and it bites hardest on short, basic, water-loving ones, which describes KPV precisely.

An HPLC purity figure is the area of the main peak as a proportion of the total peak area. It says nothing about what fraction of the powder is peptide at all. Net peptide content is the separate measurement: peptide as a proportion of everything in the vial, with the remainder being mostly counterion and water. A vial can be 99% pure by HPLC and still be a meaningful percentage acetate and moisture by mass.

The tests that close that gap are Karl Fischer for water, ion chromatography for the counterion, and amino acid analysis with mass spectrometry for identity. Counterion identity is not a formality either. Residual trifluoroacetate carried through from purification is biologically active in its own right and has been shown to affect proliferation in cultured cells, so a TFA-salt lot and an acetate-salt lot of nominally the same peptide can give you different answers.

When FDA reviewed the certificates actually supplied for KPV, it found a total impurity limit stated with no information on the nature of any single impurity, no certificate at all for the free base, and no results for aggregation or microbiological quality. Those are the specific gaps to look for.

Why endotoxin testing matters more here than usual

Endotoxin contamination is a problem for any research peptide. For KPV it is a particular problem, and the reason is worth stating plainly.

Essentially the entire published readout for KPV is suppression of NF-kB signalling and downstream inflammatory cytokine output. Bacterial endotoxin is the canonical activator of that same pathway. A contaminated lot therefore does not merely add noise, it pushes the assay in the opposite direction from the effect under study. Two lots that differ only in endotoxin load can look like they differ in potency.

The quantities involved are smaller than people expect. Work published in PLOS ONE found that human dendritic cells were activated by 0.02 ng/mL of LPS, an amount present as a trace impurity in 100 ng of a commercial recombinant protein preparation. That is why LAL testing belongs on the certificate rather than in a footnote. We cover the method families and how the limits are calculated in Endotoxin Testing Explained.

What the literature actually studies, and what it does not say

The published work on KPV is largely cell culture and rodent models: intestinal epithelial and immune cell lines, murine colitis, a rabbit corneal model, and a body of formulation work on nanoparticle and hydrogel delivery. The proposed mechanism in the more specific papers is intracellular rather than receptor-mediated, with KPV interfering with nuclear translocation of the p65 subunit of NF-kB.

Two things in that literature contradict what is commonly claimed. First, several independent papers argue that KPV does not act through melanocortin receptors. Its effect was not blocked by a melanocortin antagonist, it did not raise cAMP, and it remained active in animals with nonfunctional MC1R. Second, the melanocortin pharmacophore is His-Phe-Arg-Trp, a different fragment of alpha-MSH entirely, so descriptions of KPV as the active message sequence of the parent hormone should be treated carefully. The literature itself is not fully consistent on this point, which is a reason to read the primary sources rather than the summaries.

On human data, FDA’s 2026 review is unambiguous and worth quoting in substance: it identified no information on the use of KPV in humans, no clinical studies assessing pharmacokinetics or pharmacodynamics by any route, and no acute toxicity, repeat-dose toxicity, genotoxicity, reproductive toxicity or carcinogenicity studies. Any source describing KPV as well tolerated or extensively studied in people is describing something that has not been measured.

Where KPV stands with FDA

KPV is not an FDA-approved drug for any indication, by any route, and there is no USP monograph for it. It was nominated for the 503A bulk drug substances list and subsequently withdrawn, and it is not on the Category 2 “do not compound” list, contrary to a number of sites that describe it as banned.

In July 2026 FDA’s Pharmacy Compounding Advisory Committee considered KPV and voted in favour of adding it to the 503A list, against FDA’s own stated recommendation. That vote is advisory and non-binding. FDA is not obliged to follow it, rulemaking has not happened, and compounding with KPV is not permitted in the meantime. Coverage describing this as an approval is wrong.

Specifications

• Sequence: Lys-Pro-Val, alpha-MSH (11-13)
• Molecular formula, free base: C₁₆H₃₀N₄O₄
• Molecular weight, free base: 342.43 g/mol
• CAS: 67727-97-3
• Form: lyophilized powder
• Purity method: RP-HPLC, detection at 210 to 220 nm, no 280 nm chromophore
• Characterised major degradant: cyclo(Lys-Pro) diketopiperazine
• Guaranteed minimum purity: 98.0% chromatographic, with every published lot to date testing higher

Every lot we ship is tested by an independent laboratory before it leaves, and the certificate is published rather than provided on request. You can pull any lot number, including one you have not bought, through the lot lookup. The KPV product page is here.

References

Sources are limited to identity and nomenclature: sequence notation, registry number, formula and mass. Nothing here is cited for biological activity, and no supplier catalogue is used as a source. Each was checked on 11 August 2026. The regulatory statements were re-checked on 7 September 2026 against the FDA meeting record for the Pharmacy Compounding Advisory Committee of July 23 to 24, 2026 and legal commentary on it (Holland & Knight, August 2026): the committee recommended six of the seven peptides reviewed, KPV among them; the recommendation is nonbinding and no rulemaking has occurred.

1. IUPAC and IUBMB Joint Commission on Biochemical Nomenclature, Nomenclature and Symbolism for Amino Acids and Peptides (Recommendations 1983), published 1984, which sets the three-letter and one-letter symbol systems and the conventions for peptide and fragment notation. Full recommendations.
2. CAS Registry Number 67727-97-3, KPV (Lys-Pro-Val), free base C₁₆H₃₀N₄O₄, molecular weight 342.43. No link is given because CAS Common Chemistry carries no free public entry for this substance, which we confirmed rather than assumed, and we do not link catalogue pages as sources. The formula and mass are internally consistent and can be checked by summing standard atomic masses.

Related reading

• How to Read a Certificate of Analysis
• What Peptide Purity Actually Measures
• Endotoxin Testing Explained
• How to Store Research Peptides
• What Research Use Only Means
• Research Peptide Glossary
• All guides

For research use only. Not for human or veterinary use, ingestion, injection, or any form of in vivo administration. Not intended to diagnose, treat, cure, or prevent any disease or condition.