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Research use only
· 8 min read
Two molecules, one missing atom of nitrogen and one extra atom of oxygen. PT-141 (bremelanotide) is what you get when the C-terminal amide of Melanotan-2 is hydrolysed to a carboxylic acid - a single functional-group swap that the molecular formulae record exactly. It is a cyclic heptapeptide and a melanocortin-receptor agonist, and its identity is settled even where its precise receptor signalling is not. This is a research-context reference for its verified molecular identity, the melanocortin MC3R and MC4R pharmacology its literature describes, and bench handling. Everything below describes what published work has investigated, not any human use; PT-141 supplied by Kovalabs is for research use only, and for the full position see our research disclaimer.
| Compound | PT-141 (bremelanotide) |
|---|---|
| Synonym / INN | Bremelanotide (INN); Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH |
| Class / pharmacology | Cyclic heptapeptide; melanocortin-receptor agonist (activity at MC3R and MC4R, described in the literature as MC4R-focused) |
| Molecular formula | C50H68N14O10 |
| Molecular weight | 1025.2 g/mol |
| InChIKey | FFHBJDQSGDNCIV-MFVUMRCOSA-N |
| PubChem CID | 9941379 |
| Status | Research use only - not for human or veterinary use |
PT-141 is the cyclic heptapeptide bremelanotide, with the sequence Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH: an N-terminal acetylated norleucine, then a six-residue lactam ring closed between aspartate and lysine side chains, ending in a free carboxylic acid. It is recorded under PubChem CID 9941379, with molecular formula C50H68N14O10, molecular weight 1025.2 g/mol and InChIKey FFHBJDQSGDNCIV-MFVUMRCOSA-N. You can find PT-141 on its product page; this reference provides the research context that a product listing cannot.
The lineage is the part worth dwelling on, because it is provable from the chemistry alone rather than taken on assertion. PT-141 is the C-terminal carboxylic-acid metabolite of Melanotan-2: the same engineered backbone, with the parent peptide's terminal amide replaced by a hydroxyl (carboxylic acid). Put the two records side by side and the bookkeeping is unambiguous. Melanotan-2 (PubChem CID 92432) is C50H69N15O9 at 1024.2 g/mol; PT-141 is C50H68N14O10 at 1025.2 g/mol. Converting a primary amide (-C(=O)NH2) into a carboxylic acid (-C(=O)OH) removes one nitrogen and one hydrogen and adds one oxygen - which is precisely the difference between the two formulae (N15O9 versus N14O10), and accounts for the roughly one-mass-unit shift. The structural relationship between the two compounds is therefore not folklore; it is the kind of identity claim a mass spectrometer can settle.
That is also why the two are grouped together here. They share a molecular scaffold and a receptor family, so co-listing reflects shared melanocortin pharmacology and a direct chemical-lineage relationship, not any shared use, protocol or outcome.
| Compound | C-terminus | Molecular formula / MW | Reference identifier |
|---|---|---|---|
| PT-141 (bremelanotide) | Carboxylic acid (-OH) | C50H68N14O10; 1025.2 g/mol | PubChem CID 9941379 |
| Melanotan-2 (parent) | Primary amide (-NH2) | C50H69N15O9; 1024.2 g/mol | PubChem CID 92432 |
PT-141 is grouped pharmacologically as a melanocortin-receptor agonist. The melanocortin system comprises five G-protein-coupled receptors (MC1R through MC5R); a review of ligands for the neural melanocortin receptors by Yuan and Tao (Biomolecules, 2022; PMID 36291616, DOI) identifies MC3R and MC4R as the two subtypes expressed primarily in the central nervous system, and lists bremelanotide among the ligands that engage them. PT-141 is described in that literature as having activity at MC3R and MC4R, with the emphasis placed on MC4R. Grouping the compound by receptor occupancy rather than by any downstream readout is the honest framing: the receptors it binds are characterised, while the full consequences of that binding remain a research question.
The structural biology of the target receptor is where the evidence is strongest. Israeli et al. (Science, 2021; PMID 33858992, DOI) reported a cryo-electron-microscopy structure of the human MC4R-Gs signalling complex bound to a cyclic melanocortin agonist, resolving how an agonist occupies the orthosteric pocket and how the receptor couples to its G protein. That study did not include PT-141, so it is cited for what it establishes about the receptor itself - the architecture of the MC4R binding site and the conformational changes that accompany activation - rather than as a structure of this compound. A heptapeptide whose receptor target has been resolved at near-atomic resolution sits on far firmer mechanistic ground than most research peptides, even before any compound-specific structure exists.
An honest account has to name a constraint up front. Much of the compound-specific clinical literature on bremelanotide concerns a single registered indication, which falls outside the scope of a research-reagent reference and is not described here. What can be reported compliantly is the receptor-pharmacology and structural-biology work that characterises the melanocortin system PT-141 acts on. Each entry below names the experimental system and what it set out to resolve only.
No compound-specific structure of a PT-141-receptor complex was located in the structural databases at the time of writing, so none is cited as one. Where the only well-characterised pharmacology is the receptor family rather than the molecule, this page says so plainly rather than padding the gap.
The following is general bench procedure for lyophilised research peptides, framed for laboratory use only. It is not a preparation method for any use in humans or animals.
Storage: keep the dry, lyophilised powder desiccated and frozen (commonly -20 degrees C, and -20 to -80 degrees C for long-term archival), protected from moisture and light. Allow a sealed vial to equilibrate to room temperature in a desiccator before opening, so condensation does not settle onto the hygroscopic solid and bias gravimetric and concentration measurements.
Reconstitution as a bench procedure: for analytical assay use, add appropriate laboratory solvent slowly down the inner wall of the vial and swirl gently rather than shaking or vortexing, to avoid mechanical and foaming stress on a cyclic peptide. Use the reconstituted solution within a defined working window for analysis and keep it refrigerated (2 to 8 degrees C) during that window. Our reconstitution guide covers the general method in more detail.
Purity and certificate of analysis: peptide identifiers are easy to get wrong on paper, and a vial that says one thing is not the same as a vial that is one thing. For a cyclic heptapeptide this matters twice over, because the parent amide and the acid metabolite differ by a single functional group and roughly one mass unit - a difference a careful mass spectrometer resolves and a careless label does not. Identity and quality are established analytically by reversed-phase HPLC for purity and mass spectrometry for identity; a correct mass match combined with high HPLC purity is the standard evidence that the intended peptide is present. A batch-specific Certificate of Analysis should document the actual lot tested rather than a generic specification; current documents are available on our Certificates of Analysis page.
The chemistry is solid. PT-141 is unambiguously the cyclic heptapeptide bremelanotide, Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH, the carboxylic-acid metabolite of Melanotan-2, and its public-database identifiers, molecular formula and the one-functional-group difference from its parent all cross-check and agree. The receptor pharmacology is the middle ground: PT-141 is characterised as a melanocortin-receptor agonist with MC3R and MC4R activity, and the MC4R itself has been resolved structurally with an agonist bound - but a receptor characterised in vitro and by structural biology is not a defined outcome in an organism, and no compound-specific structure of PT-141 has been reported. The human tier is the weakest here by design of this page: the research-reagent context deliberately leaves out the registered clinical indication, so as a laboratory reagent it has not been shown to produce any defined outcome. It is not a licensed medicine, and nothing here describes a use.
PT-141 supplied by Kovalabs is sold strictly as a research chemical for in-vitro and laboratory use by qualified researchers. It is not a medicine, supplement, cosmetic or food, and it is not for human or veterinary use, administration or consumption. Nothing on this page is medical, dosing or administration guidance, and no therapeutic, clinical or performance benefit is stated or implied. Under MHRA Guidance Note 8, a benefit claim would reclassify a research chemical as an unlicensed medicine; we make no such claim. Full terms are set out in our research disclaimer.
PT-141 is the cyclic heptapeptide bremelanotide, Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH, recorded under PubChem CID 9941379 with molecular formula C50H68N14O10 and molecular weight 1025.2 g/mol; see the identifiers table above. It is a research chemical, not a medicine.
PT-141 is the C-terminal carboxylic-acid metabolite of Melanotan-2: the same cyclic backbone with the parent peptide's terminal amide replaced by a carboxylic acid. The formulae record the swap exactly - Melanotan-2 is C50H69N15O9 (CID 92432) and PT-141 is C50H68N14O10 (CID 9941379), a loss of one nitrogen and gain of one oxygen consistent with amide-to-acid hydrolysis.
Published literature describes PT-141 as a melanocortin-receptor agonist with activity at the neural melanocortin receptors MC3R and MC4R, with emphasis on MC4R (PMID 36291616). The MC4R has separately been resolved by cryo-EM bound to a melanocortin agonist (PMID 33858992). These are receptor and structural-biology observations from study designs; no effect or human outcome is asserted.
General peptide practice is to store the lyophilised powder desiccated and frozen, equilibrate the vial to room temperature before opening, and reconstitute by adding appropriate laboratory solvent gently down the vial wall, using the solution within a defined working window and keeping it cold. See our reconstitution guide for the general method. This is bench procedure only, not an administration instruction.
For a cyclic heptapeptide, identity is confirmed by mass spectrometry and purity by reversed-phase HPLC; a correct mass match with high HPLC purity is the standard evidence. This matters because the acid metabolite and its parent amide differ by roughly one mass unit. Each batch should carry a lot-specific Certificate of Analysis, available on the Kovalabs Certificates of Analysis page.
No. PT-141 is supplied for research use only and is not for human or veterinary use, administration or consumption. No medicinal, therapeutic or performance benefit is stated or implied, consistent with MHRA Guidance Note 8. See the research disclaimer for full terms.