Compound reference
PT-141: structure and analysis
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PT-141 is a melanocortin receptor ligand supplied for laboratory research. Its molecular formula is C50H68N14O10, with an average molecular weight of 1025.2 g/mol and a monoisotopic mass of 1024.524 Da. This page covers its structure, how it is produced, and how identity and purity are established — for a batch, on that batch's certificate of analysis.
What is PT-141?
PT-141, also known as bremelanotide, is a synthetic cyclic heptapeptide active at melanocortin receptors. Structurally it is a metabolite of melanotan II: the same seven-residue cyclic scaffold, differing at the C-terminus.
That difference is small in mass terms and significant in identity terms. The two compounds are separate molecules with separate specifications, and they are routinely conflated in this category.
How is PT-141 produced?
Assembled by solid-phase peptide synthesis: the chain is built one residue at a time on an insoluble resin support, then cleaved from the resin, deprotected and purified — most commonly by reversed-phase high-performance liquid chromatography. The purified material is lyophilized to a dry solid.
The impurity profile that appears on a certificate is a record of where that process was imperfect: deletion sequences from an incomplete coupling, truncated chains, and species retaining a protecting group.
What are the molecular figures for PT-141?
Calculated from the formula C50H68N14O10, not measured. The average molecular weight counts the natural abundance of each element's isotopes; the monoisotopic mass is the mass of the single most abundant isotopic composition, which is the figure a mass spectrometer is usually compared against.
The expected ions follow from the monoisotopic mass by adding one proton per charge. They are a starting point for recognising a spectrum, not a substitute for one: adducts, salts, modifications and multiply charged species all move the observed m/z, and the certificate reports what was actually measured for a batch.
Adducts, salts, modifications and multiply charged species all move an observed m/z away from any figure calculated here, and a certificate reports what was measured for a batch rather than what was expected of it.
What is the sequence of PT-141?
No one-letter amino-acid sequence is published for PT-141 on this page. The chain contains norleucine and a D-amino acid, neither of which has a standard one-letter code, and the N-terminus is acetylated.
What establishes the material in a specific vial is the identity method and result stated on that batch's certificate, not a notation on a reference page.
How does PT-141 compare with related compounds?
Related compounds are not interchangeable. Published figures differ between them, and in this catalogue three compounds share a GHRH backbone while several share the same structural class — which is exactly why identity is confirmed analytically rather than inferred from the label.
How is the identity of PT-141 confirmed?
Two things need confirming here rather than one. Mass spectrometry establishes that cyclisation occurred — the ring-closed product has a lower mass than the linear precursor by a predictable amount — and it establishes which of the two closely related cyclic heptapeptides is present.
The second is the harder measurement. The mass difference between this compound and melanotan II is small enough that a low-resolution instrument cannot settle it, so the resolution of the identity method is a substantive parameter rather than a technicality.
Which impurities can appear in PT-141?
Because the compound and its structural parent differ so little in mass, chromatographic resolution shares the identity burden with mass spectrometry. The two species separate on a well-developed reversed-phase method, and that separation is part of what a purity figure for this compound is actually demonstrating.
The uncyclised linear precursor is the other impurity class specific to a cyclic peptide, and it is distinguishable both by mass and by retention.
Cyclisation also makes the molecule a poorer protease substrate than a linear heptapeptide, which contributes to its stability as a dry solid.
What does a certificate of analysis for PT-141 report?
A certificate for a batch of this material names the batch, names the issuing laboratory, and states for each parameter both the method used and the specification the result was measured against. Identity and purity are the two core results; net peptide content states how much of the fill weight is actually peptide.
A certificate belongs to a batch, not to a product line. When a new batch is released it is tested again, and the certificate published against it is that batch's certificate — a previous batch's result is never carried forward.
Is PT-141 for human use?
No. This page describes structure and analysis. It makes no claim about what this compound does, and none should be inferred from it. Material is supplied for laboratory research use only: it is not a drug, food, dietary supplement, cosmetic or medical device, it is not for human or veterinary consumption, and no dosing, administration or reconstitution guidance is provided for any such use.
References
- Bremelanotide (PT-141) — PubChem, National Library of Medicine
- Bremelanotide Acetate — ChEMBL, European Bioinformatics Institute
- LC-HRMS characterization of the skin pigmentation and sexual enhancers melanotan II and bremelanotide sold on the black market of performance and image enhancing drugs — Drug Test Anal, 2021
From the catalog
Compounds referenced on this page
For laboratory research use only. Not for human or veterinary consumption.