Bremelanotide vs Melanotan II: Related Scaffolds, Different Research Records
Bremelanotide and Melanotan II are closely related cyclic melanocortin peptides, but they should be documented as separate molecular and evidence records. Bremelanotide, also called PT-141, is the deamidated form related to the Melanotan II scaffold. That terminal difference changes the molecular formula and mass. It does not erase the shared cyclic core, and it does not make results from one peptide automatically transferable to the other.
The exact catalog entries are Bremelanotide (PT-141) and Melanotan II (MT-2). A related overview, the melanocortin research materials map, places both within the broader receptor family while preserving each compound’s identity.
How are the two structures related?
Melanotan II is commonly written as a cyclic heptapeptide with an amidated C-terminus. Bremelanotide retains the cyclic peptide scaffold but has the corresponding free carboxyl terminus rather than the terminal amide. This is often described as deamidation. Because -CONH2 and -COOH are different chemical groups, the records need different formulas, expected masses, and reference standards.
Both compounds have been characterized with high-resolution mass spectrometry. A forensic analytical study used accurate precursor mass, isotope patterns, and collision-induced product ions to distinguish unknown samples containing the two compounds. The LC-HRMS study supports the value of exact-mass and fragmentation evidence; it does not certify any product outside the samples tested.
| Comparison field | Melanotan II | Bremelanotide / PT-141 | Why the field matters |
|---|---|---|---|
| Peptide family | Cyclic alpha-MSH analogue | Related cyclic alpha-MSH analogue | Shared family does not mean identical material |
| C-terminus | Amidated | Free carboxyl form | Changes formula, exact mass, charge behavior, and naming |
| Receptor literature | Often described as broad across several melanocortin receptors | Frequently studied with emphasis on MC3R and MC4R | Assay panel and concentration determine the claim |
| Analytical confirmation | Intact mass plus diagnostic fragments | Intact mass plus diagnostic fragments | Retention time alone is weak identity evidence |
| Evidence transfer | Applies to the exact tested MT-II material and model | Applies to the exact tested PT-141 material and model | Results should not be pooled under one nickname |
Receptor-family language needs an assay panel
Calling a peptide a “melanocortin agonist” identifies a receptor family, not a complete selectivity profile. Potency and efficacy should be reported by receptor subtype, cell system, readout, exposure time, and concentration range. An older PT-141 research report describes activity at melanocortin receptors including MC3R and MC4R and includes several distinct experimental models. The PT-141 paper is evidence for its stated assays and models, not a universal receptor ranking.
Research on Melanotan II derivatives also shows that small backbone changes can shift receptor-subtype selectivity. A systematic N-methylation study tested a library against human MC1R, MC3R, MC4R, and MC5R. Its results concern those designed derivatives, but they demonstrate why a related scaffold cannot be assigned a fixed profile without direct testing.
The peptide stereochemistry guide adds another important point: a correct nominal sequence is incomplete if D-residues, cyclization, or terminal chemistry are omitted. The research peptide naming guide explains how aliases such as PT-141 and MT-2 should be tied back to unambiguous molecular descriptions.
What should an identity record contain?
For either peptide, document the full sequence notation, D-amino-acid configuration, cyclization connection, C-terminal form, counterion if reported, expected molecular formula, and expected monoisotopic or average mass. An LC-MS result should show the assigned charge state and isotopic envelope. MS/MS should include product ions that help locate the terminal and sequence features rather than only confirming a shared core.
Chromatographic purity adds another dimension but cannot replace identity. Two related peptides may each produce a dominant peak under one method, while only accurate mass and fragment evidence distinguish them. Lot-specific documentation in the COA library should therefore be read field by field. The Research Compounds collection and NEXTWAVE PEPTIDES catalog organize related materials without implying interchangeability.
A reference standard should match the exact terminal form. If the standard is Melanotan II while the target is bremelanotide, similar retention or shared fragment ions are not enough to establish a complete match. The report should name the standard and identify which ions distinguish the terminal amide from the free acid.
Research limitations
Published receptor results vary with species, receptor construct, cell background, signaling readout, concentration, and timing. Forensic identification of unknown samples shows analytical discrimination, not biological equivalence or product quality. A paper on one peptide does not verify a separate lot, and shared scaffold terminology does not establish the same receptor profile. This article addresses molecular identity and research evidence, not human-use directions.
Frequently asked questions
Is PT-141 another name for bremelanotide?
Yes. PT-141 is a widely used development and research name for bremelanotide.
Is bremelanotide identical to Melanotan II?
No. They share a closely related cyclic scaffold, but their C-terminal chemistry differs. That difference changes the molecular record.
Can LC retention time alone distinguish them?
Retention time can support a match under a fixed method, but stronger identity evidence combines a reference standard with accurate mass, isotope pattern, and diagnostic fragmentation.
Do both peptides have the same receptor selectivity?
That should not be assumed. Receptor-subtype results depend on the exact molecule and assay design, so each evidence record must be read separately.