Description
PrymaLab · Research Use Only
PT-141 10mg
A ring closed by an amide bond · and the eighteen daltons that prove it
PT-141 peptide is not a chain. It is a ring, closed by an amide bond formed between two side chains rather than between the ends of the molecule, and forming that bond releases a water molecule. Eighteen daltons is therefore the number that proves the article is what it claims.
Specification Table
| Property | Value |
|---|---|
| Compound | PT-141 |
| International nonproprietary name | Bremelanotide |
| Class | Cyclic melanocortin receptor agonist |
| Residue count | 7 |
| Topology | Cyclic. A side-chain to side-chain lactam bridge between an aspartate and a lysine |
| Molecular weight, calculated | Approximately 1,025.2 g/mol |
| CAS | 189691-06-3 |
| Amino terminus | Acetylated |
| Carboxy terminus | Free acid |
| Mass consequence of cyclisation | Ring closure eliminates water, so the cyclic form is eighteen daltons lighter than the linear precursor |
| The check that follows | A mass eighteen high indicates uncyclised material |
| Regulatory status | Holds an approved human formulation in the United States |
| Relationship to that product | Material supplied here is not that product and is not manufactured to pharmaceutical standards |
| Appearance | White lyophilized powder |
| Storage, lyophilized | 2-8°C short term, -20°C for extended storage, protected from light and moisture |
What Is the Lactam Bridge in PT-141 Peptide?
Most peptides in this catalogue are linear chains with two ends. PT-141 peptide is a loop, and the way that loop closes drives everything analytical about the molecule.
A lactam is simply an amide bond formed inside a ring. Here it forms between the side-chain carboxyl of an aspartate and the side-chain amine of a lysine.
Those two residues sit several positions apart in the sequence, so joining their side chains pulls the intervening stretch into a closed loop.
The chemistry is the same as an ordinary peptide bond and the geometry is entirely different, because the bond runs across the molecule rather than along it.
Constraining a peptide this way is a well-established design strategy and its purpose is conformational.
A linear peptide samples an enormous number of shapes in solution, only one of which fits a receptor. A cyclised one is locked into a much smaller set.
That raises binding affinity where the locked conformation is the productive one, and it improves resistance to proteases at the same time, because a constrained backbone presents poorly to an active site.
The trade is that cyclisation is a synthesis step that can fail, and a failed one gives a molecule that looks almost identical to pt-141 peptide on a certificate.
Which is the subject of the next section, and the single most useful check available on this article.
Why Eighteen Daltons Settles It
Forming an amide bond joins a carboxyl to an amine and eliminates a molecule of water in the process.
Water is eighteen daltons. So the cyclic product weighs eighteen daltons less than the linear precursor it was made from.
On a molecule of roughly 1,025 daltons that is about 1.7 percent, which any mass spectrometer resolves comfortably and a high-resolution instrument resolves trivially.
The check on pt-141 peptide is therefore direct. A certificate quoting approximately 1,025 describes cyclised material. One quoting approximately 1,043 describes the linear precursor.
That second number means the cyclisation step did not complete. The material shipped anyway, which is a real failure mode rather than a theoretical one.
A partly cyclised preparation is worse than either pure form. It is a mixture of two molecules with different conformational behaviour in unknown proportion.
Chromatography detects it too. A constrained ring is more compact than an open chain, so the two elute differently.
The linear form generally elutes later, being more exposed. The direction depends on the gradient and should not be assumed.
Of the two, mass is decisive. Eighteen daltons is a number rather than a relative position.
Almost no certificate reports the comparison explicitly. Asking for the calculated figure alongside the observed one costs nothing at all.
One qualification on reading a mass figure for a cyclic peptide.
Mass spectrometers report the mass of an ion rather than of a neutral molecule, so the number on a certificate depends on which adduct was observed and on the charge state.
A figure quoted without that context can differ from the calculated neutral mass by a proton or by a sodium, which is small and is enough to muddle an eighteen-dalton comparison if nobody states the basis.
What Does the Approval Change?
PT-141 peptide holds an approved human formulation in the United States, which is unusual in this catalogue and worth stating with its boundaries attached.
That approval belongs to a specific pharmaceutical product, manufactured under pharmaceutical controls, filed and reviewed for one defined indication.
Material supplied here is research-grade under research-use-only terms and is not that product. No equivalence between the two has been demonstrated for any particular lot.
What the approval does provide is a published clinical record generated to regulatory standard, including controlled trials with prespecified endpoints.
That is a considerably better evidence base than most compounds in this range have, and it is readable by anyone planning work.
The caveats travel with it. Those trials studied one indication, one formulation and one route, and results outside that envelope are extrapolation rather than data.
The approval also says nothing about the article in this vial beyond establishing that the molecule can be made to a standard a regulator accepted.
For a researcher the practical value is a well-characterised reference point. The published pharmacokinetics and the receptor pharmacology are known quantities rather than estimates.
Reading the regulatory record and then verifying the vial is the sequence that makes sense, and the eighteen-dalton check is what does the second half.
What Should a PT-141 Certificate Show?
A pt-141 peptide certificate carries seven fields, and the first three follow from the ring.
The full construct written out, including which residues form the bridge and the configurations at each position. A trade name does not specify a topology.
Observed mass against calculated mass, with the calculated figure printed. Approximately 1,025 is the cyclic article.
Explicit confirmation that the material is cyclised, stated rather than left to inference.
Whether the amino terminus is acetylated, which is part of the definition of this molecule and is a routine synthesis omission.
Purity by reverse-phase HPLC with the chromatogram supplied, since the uncyclised species and any deletion sequences resolve by retention.
Counterion identity alongside net peptide content. An arginine and a histidine sit beside the bridged lysine, so the construct is basic overall and carries a trifluoroacetate load that is not trivial.
Lot number and synthesis date.
A certificate stating both the observed mass and the calculated one for the cyclic form does the whole job in two lines. Most do not.
Why Does the Sequence Contain Norleucine?
One residue in pt-141 peptide is not a standard amino acid, and it is there to solve a specific problem.
Position one carries norleucine, an unbranched six-carbon residue that does not appear in the genetic code.
The parent hormone this analogue derives from carries a methionine at the corresponding position instead.
Methionine has a sulfur atom in its side chain, and sulfur oxidises readily under ordinary storage conditions to give the sulfoxide.
That reaction adds sixteen daltons and produces a chemically different molecule, which is a liability for any compound intended to sit in a vial.
Norleucine has the same length and shape as methionine and no sulfur. It occupies the same space in a binding site and has nothing to oxidise.
Substituting it was one of the earliest moves in melanocortin analogue design and it is why this compound is far more stable than its natural parent.
The practical consequence is that the oxidation checks required for a methionine-containing peptide do not apply here.
There is no sixteen-dalton species to look for and no polar early-eluting peak to interpret, because the residue that would produce them was designed out.
That is a useful contrast to keep in mind when comparing across this catalogue, because two peptides of similar size can have entirely different storage requirements for one residue.
It is also a reasonable question to ask a supplier. A certificate listing methionine at position one describes a different molecule.
How Should the Vial Be Handled?
No cysteine and no methionine makes pt-141 peptide a chemically well behaved molecule, so the handling section is shorter than most in this catalogue.
Sealed dry powder holds at refrigeration temperature briefly and at minus 20 for longer, with light and moisture both excluded.
Warm the vial before opening it. The powder is hygroscopic and cold glass condenses atmospheric water straight onto the cake.
Add the diluent down the wall and swirl. Shaking drives peptide to the air-liquid interface, which is where aggregation starts.
The lactam bridge is a stable amide bond and it does not open under ordinary storage or handling conditions, unlike a disulfide.
That is a genuine advantage of this design over a cysteine-constrained peptide, and it means no reducing-agent precaution is needed here.
Aliquot on first reconstitution. Freeze-thaw cycling is the usual avoidable loss, and a cyclic molecule is no more immune to it than a linear one is.
Use low-binding consumables once the solution is dilute, because ordinary plastics take up a measurable share of any peptide at low concentration.
Record lot, the observed mass, net peptide content, diluent volume and date. Carrying the mass forward makes the cyclisation check part of the provenance.
A closing note on what the absence of a disulfide is worth.
Several articles in this catalogue need a check on every buffer and culture component for reducing species, because a reduced bridge is an unrecoverable change.
None of that applies here. The lactam is an ordinary amide bond and it survives anything a peptide preparation would ordinarily meet.
That is one fewer variable in the record and one fewer way for a preparation to fail quietly, which is worth knowing when choosing between constrained peptides.
Published Literature
Selected references on cyclic melanocortin analogue design, on this compound and on its clinical evaluation.
- Al-Obeidi F, Castrucci AM, Hadley ME, Hruby VJ. Journal of Medicinal Chemistry. 1989;32(12):2555-2561. DOI: 10.1021/jm00132a010
- Molinoff PB, Shadiack AM, Earle D, Diamond LE, Quon CY. Annals of the New York Academy of Sciences. 2003;994:96-102. DOI: 10.1111/j.1749-6632.2003.tb03167.x
- Hadley ME. Peptides. 2005;26(10):1687-1689. DOI: 10.1016/j.peptides.2005.01.023
- Kingsberg SA, Clayton AH, Portman D, Williams LA, Krop J, Jordan R, et al. Obstetrics and Gynecology. 2019;134(5):899-908. DOI: 10.1097/AOG.0000000000003500
Frequently Asked Questions
What is PT-141 peptide?
A cyclic seven-residue melanocortin receptor agonist, also called bremelanotide, calculated at approximately 1,025 daltons and carrying CAS 189691-06-3.
What makes it cyclic?
A lactam bridge, which is an amide bond formed between the side-chain carboxyl of an aspartate and the side-chain amine of a lysine several positions away.
Why cyclise a peptide at all?
To constrain its shape. A linear peptide samples many conformations in solution and only one usually fits the receptor. Locking the shape raises affinity and improves protease resistance.
What is the eighteen-dalton check?
Forming the amide bond eliminates a molecule of water, so the cyclic product weighs eighteen daltons less than the linear precursor. That difference proves the ring closed.
What mass indicates a problem?
Approximately 1,043 rather than 1,025. That is the linear precursor, meaning the cyclisation step did not complete and the material shipped anyway.
Why is partial cyclisation worse than either pure form?
Because it is a mixture of two molecules with different conformational behaviour in unknown proportion, and nothing about the vial reveals the ratio.
Can chromatography detect it?
Yes. A constrained ring is more compact than an open chain and the two elute differently, though the direction depends on the gradient and should not be assumed.
Which method is more decisive?
The mass. Eighteen daltons is an absolute number, whereas a retention difference is a relative position that depends on the method used.
Does it hold an approval?
Yes, an approved human formulation in the United States for one defined indication. That approval attaches to a specific pharmaceutical product manufactured under pharmaceutical controls.
Is this that product?
No. Material supplied here is research-grade under research-use-only terms and no equivalence with the approved article has been demonstrated for any particular lot.
Does the ring need protecting like a disulfide?
No. The lactam bridge is a stable amide bond and does not open under ordinary storage or handling, so no reducing-agent precaution is needed. That is a real advantage of the design.
What should go in the record?
Lot, the observed mass from the certificate, net peptide content, diluent volume and date. Carrying the mass forward makes the cyclisation check part of the provenance rather than a one-off.
Compliance Statement
PT-141 peptide is sold exclusively for laboratory research use. It is not a drug, food, or cosmetic product, and it is not a dietary product of any kind. It is not approved by the FDA or any comparable authority for human or veterinary use, it holds an approved human formulation in the United States for one defined indication but material supplied here is not that product and is not manufactured to pharmaceutical standards, published trial data was generated with the approved formulation by a single route and results outside that envelope are extrapolation, and no compound in this range is offered for any human or veterinary purpose. This product is not intended to diagnose, treat, cure, or prevent any disease. It must not be given to humans or animals. Purchase is restricted to qualified researchers and institutions operating within applicable laws. All handling is the responsibility of the purchasing laboratory.
Other formats of PT-141
PT-141 is also stocked as PT-141 10mg/ml preloaded 3ml pen and PT-141 Peptide Nasal Spray. Each listing states its own quantity and concentration, and the pen and vial comparison explains what changes between formats. The PT-141 sourcing and certificate guide covers what to check on a certificate before ordering.
21 reviews for PT-141 10mg