Compound monograph
PT-141 (Bremelanotide)
PT-141, canonically bremelanotide, is a synthetic cyclic heptapeptide melanocortin receptor agonist, structurally the C-terminal free acid of the Melanotan II lactam scaffold.
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Identity & nomenclature
PT-141, canonically bremelanotide, is a synthetic cyclic heptapeptide melanocortin receptor agonist, structurally the C-terminal free acid of the Melanotan II lactam scaffold.
Bremelanotide is the canonical substance name; PT-141 is the development code and the name under which the compound is most often supplied. Both denote the same molecule. The compound is structurally the C-terminal free acid of the Melanotan II scaffold — the two share a carbon count and differ by one oxygen for one nitrogen and one hydrogen. Chen et al. (PMID 32674774) describe bremelanotide as deamidated Melanotan II and as a metabolite of Melanotan II.
Canonical name: Bremelanotide.
Declared aliases and development codes: Bremelanotide, PT 141, PT-141 free base, PT-141.
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Molecular properties
| Molecular formula | C50H68N14O10 |
|---|---|
| Molecular mass | 1025.17 Da |
| CAS Registry Number | 189691-06-3 |
| PubChem CID | 9941379 |
| UNII | 6Y24O4F92S |
| Three-letter sequence | Nle–Asp–His–D-Phe–Arg–Trp–Lys |
| Terminal groups | N-terminal acetylation; C-terminal free acid |
As with Melanotan II, no linear one-letter string is published here: the peptide is closed by a lactam bridge between the aspartate side-chain carboxyl and the lysine side-chain amine. The single structural difference from Melanotan II is at the C-terminus, which is a free acid rather than an amide. FDA GSRS (UNII 6Y24O4F92S) records the same Asp2-Lys7 side-chain amide; no paper giving both ring positions for the free acid itself is cited here.
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Structural characteristics
A cryo-electron microscopy structure of bremelanotide bound to the melanocortin-4 receptor in complex with heterotrimeric Gs protein has been determined, making this one of the few compounds in this library for which an exact-compound receptor-bound structure exists rather than an analog structure. The same work reports structures of the receptor bound to alpha-MSH, to afamelanotide and to a small-molecule ligand, and describes a conserved binding mode across the peptide agonists. Separate work on the activation mechanism of the same receptor used NDP-alpha-MSH and setmelanotide rather than bremelanotide; findings from that work describe the receptor, not this compound.
- Side-chain to side-chain lactam bridge, Asp to Lys
- Norleucine substitution
- D-phenylalanine substitution
Ring closures: covalent bonds between residues, by position counted from the first residue of the chain.
- Side-chain lactam Asp2–Lys7: side-chain carboxyl (Cγ) to side-chain ε-amino nitrogen (Nζ). Registry source: FDA GSRS UNII 6Y24O4F92S; PubChem CID 9941379.
Terminal features: N-terminal acetylation, C-terminal free acid.
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Molecular targets & mechanisms
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Analytical considerations
See the Melanotan II entry for the full statement of the mass question; it applies symmetrically. The calculated neutral monoisotopic mass of PT-141 is 1024.52428 against 1023.54027 for Melanotan II, and the average masses are 1025.17 and 1024.18 — so the two do not share a rounded mass, and a measurement reported to adequate precision separates them. What does not separate them is a check for a signal near 1024.5, because Melanotan II's first carbon-13 peak sits within 0.0194 Da of PT-141's monoisotopic value. In the direction that matters commercially, material sold as PT-141 is not shown to be PT-141 rather than Melanotan II by a single rounded mass, by retention time on a method never demonstrated to resolve the pair, or by a purity figure. What does establish it is high-resolution mass spectrometry at sufficient resolving power for that specific separation, or a chromatographic method validated to discriminate the amide from the acid against reference material — and in either case the method has to have been chosen with this question in mind.
Disagreements and mix-ups
Points where sources disagree about this compound's identity, or where a name or form is easily confused with another, as noted in this record. The discrepancy register quotes the passage for each one.
Often mixed up · Name or substance
Melanotan II vs PT-141: C-terminal amide vs free acidAlso noted in Melanotan II
What the studies reported
Each finding describes one cited study in its stated model. These observations are specific to that study and do not establish effects in other settings.
Cell and tissue studies
MC4R-Gs receptor complex
Zhang et al. reported a high-resolution structure of full-length MC4R in complex with heterotrimeric Gs protein and bremelanotide in vitro.
Reference [1]
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Verified bibliography
Cited studies by type
The 4 papers this record cites, counted by the kind of work each reports. A count is the size of this record's selection, not of the research that exists, and says nothing about results, safety, effectiveness or approval.
A paper can report more than one kind of work. Each count opens those papers in the bibliography. Compare every record on the Evidence Map.
Reference 1
Structural insights into ligand recognition and activation of the melanocortin-4 receptor.Zhang H, Chen LN, Yang D, Mao C, Shen Q, Feng W, Shen DD, Dai A, Xie S, Zhou Y, Qin J, Sun JP, Scharf DH, Hou T, Zhou T, Wang MW, Zhang Y
Cell research · 2021-08-25 · Journal Article
currentReference 2
Structures of active melanocortin-4 receptor-Gs-protein complexes with NDP-α-MSH and setmelanotide.Heyder NA, Kleinau G, Speck D, Schmidt A, Zschunke S, Szczepek M, Bauer B, Koch A, Gallandi M, Kwiatkowski D, Bürger J, Mielke T, Beck-Sickinger AG, Hildebrand PW, Spahn CMT, Hilger D, Schacherl M, Biebermann H, Hilal T, Kühnen P, Kobilka BK, Scheerer P
Cell research · 2021-09-24 · Journal Article
currentReference 3
Goldilocks-Inspired Design of Mid-Size Macrocycles for Selective Targeting of Human Melanocortin Receptors.Merlino F, Jia L, Boccino I, Carotenuto A, Tammaro F, Santoro F, Thompson PE, Grieco P
Journal of medicinal chemistry · 2026-08-13 · Journal Article
currentReference 4
Combining MALDI mass spectrometry imaging and droplet-base surface sampling analysis for tissue distribution, metabolite profiling, and relative quantification of cyclic peptide melanotan II.Chen B, Vavrek M, Gundersdorf R, Zhong W, Cancilla MT
Analytica chimica acta · 2020-05-24 · Journal Article
current
Study models of these references
What kind of experiment each cited paper reports, taken from its abstract unless marked. Not a summary of results.
| Reference | Study models |
|---|---|
| Zhang H et al. 2021 | Study models reported: in vitro · from the abstract |
| Heyder NA et al. 2021 | Study models reported: in vitro · from the abstract |
| Merlino F et al. 2026 | Study models reported: in vitro · from the abstract |
| Chen B et al. 2020 | Study models reported: animal (mouse) · from the abstract |
Compare
Record history
Published 2026-09-13.
- : Sequence and structure
- : Identity and nomenclature, Sequence and structure, References
- : Analytical notes
Each entry names the parts of this record that changed on that date. Changes to links between records and to catalogue links are not listed. This history covers the tracked record fields; study findings are not listed here.
Cite this record: Purely Peptides Research Library. PT-141 (Bremelanotide). Published 2026-09-13; updated 2026-10-15. https://purelypeptides.org/research/compounds/pt-141/
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Methodology & citation verification
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