Melanotan-2 (MT-2) is a synthetic cyclic heptapeptide analogue of alpha-melanocyte-stimulating hormone (α-MSH), catalogued under CAS 121062-08-6. It is one of the most thoroughly characterised non-selective melanocortin receptor agonists in the pharmacology literature, and is widely used as a reference ligand in receptor-binding work.
This page is a reference document for qualified research personnel evaluating MT-2 for in vitro and non-clinical work. It covers the molecule's structure and identifiers, the receptor subtypes it appears against in published literature, how it is distinguished from two compounds it is routinely confused with, and how batch documentation should be assessed. No preparation, dosage, or administration guidance is provided anywhere on this page. For the wider catalogue context, see research peptides in Canada.
Scope note: NexPept supplies peptide compounds strictly for laboratory research use. Nothing below describes a therapeutic or cosmetic application, and no statement here should be interpreted as a clinical or health claim. See the regulatory notice at the end of this page.
What Melanotan-2 is
MT-2 was developed at the University of Arizona by Mac Hadley and Victor Hruby as part of a programme to produce metabolically stable analogues of α-MSH. Native α-MSH is a linear peptide that does not hold a single conformation in solution, which limits its usefulness as a research ligand. MT-2 solves that problem structurally.
Three modifications define the molecule. L-methionine is replaced with the isosteric, non-oxidisable L-norleucine. L-phenylalanine is replaced with its D-enantiomer. And a lactam bridge between the aspartate and lysine side chains closes the sequence into a 23-membered macrocycle, locking the pharmacophore residues into a fixed conformation that the linear parent cannot maintain.
The result is a conformationally constrained cyclic heptapeptide with markedly greater stability than α-MSH — which is precisely why it remains a standard tool compound in melanocortin receptor research decades after its synthesis.
Molecular profile
MT-2 is produced by solid-phase peptide synthesis and characterised by reversed-phase HPLC with mass spectrometric confirmation. The identifiers below are what a laboratory would use to verify received material against a certificate of analysis.
| Property | Value |
|---|---|
| CAS Number | 121062-08-6 (free peptide) |
| Molecular Formula | C50H69N15O9 |
| Molecular Weight | 1024.18 Da (average); 1023.54 Da (monoisotopic) |
| Sequence | Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2 |
| Chain Length | 7 amino acids (cyclic) |
| Compound Class | Synthetic cyclic heptapeptide amide; α-MSH analogue |
| Structural Feature | 23-membered lactam macrocycle (Asp–Lys side-chain bridge) |
| Terminal Modifications | N-terminal acetyl; C-terminal amide |
| PubChem CID | 92432 |
| Also Known As | Melanotan II, MT-II, MTII |
| Physical Form | Lyophilized powder |
| Appearance | White to off-white powder |
| Analytical Method | RP-HPLC + MS |
Verification tip: CAS 121062-08-6 identifies the free peptide — not an acetate salt, a vial size, or a purity grade. When checking a COA, confirm the observed mass against 1024.18 Da and verify that the acetyl and amide terminal modifications are accounted for, since an unmodified linear sequence of the same residues is a different compound.
Melanocortin receptor targets
The melanocortin system comprises five G-protein-coupled receptor subtypes. MT-2 is described in the literature as a non-selective agonist across four of them — which is both the reason it is useful as a broad reference ligand and the reason selective analogues were subsequently developed. The headings below describe where the compound appears in published receptor pharmacology, not outcomes of any kind.
Non-selectivity is the defining pharmacological characteristic here. A compound that engages four of five subtypes is a blunt instrument in any model designed to isolate a single pathway, and research designs frequently pair MT-2 with a selective analogue specifically to separate subtype contributions.
MT-2 vs Melanotan-1 vs PT-141
Three distinct compounds sit close together in this space, and mislabelling between them is common enough in the research-supply market to warrant checking every time. They share a lineage but are structurally and analytically different materials.
| Property | Melanotan-2 | Melanotan-1 | PT-141 |
|---|---|---|---|
| CAS Number | 121062-08-6 | 75921-69-6 | 189691-06-3 |
| Other Name | MT-II | Afamelanotide | Bremelanotide |
| Structure | Cyclic heptapeptide | Linear 13-residue amide | Cyclic heptapeptide |
| Molecular Weight | 1024.18 Da | 1646.85 Da | 1025.16 Da |
| C-Terminus | Amide | Amide | Carboxy group |
| Receptor Profile | Non-selective (MC1R, MC3R, MC4R, MC5R) | Described as MC1R-preferring | Described as MC4R-preferring |
The critical check: PT-141 is a close structural relative of MT-2 — it differs principally in carrying a carboxy group where MT-2 carries an amide — and their molecular weights sit roughly one dalton apart. A listing quoting CAS 75921-69-6 or 189691-06-3 for material labelled Melanotan-2 is mislabelled, and mass alone will not reliably separate MT-2 from PT-141 without adequate instrument resolution.
What the evidence does and does not show
Accurate characterisation of the evidence is part of good research practice. The following is a plain statement of where things stand.
What exists
What does not exist
Purity, batch testing and COAs
Cyclic peptides carry verification considerations that linear sequences do not. An incomplete cyclisation, a residual linear precursor, or a missing terminal modification all produce material that is close to the target in mass but different in behaviour. Documentation matters accordingly.
NexPept publishes batch certificates for catalogue compounds in a single searchable location, so a batch code can be cross-referenced before material enters a protocol. The same standard applies across the research peptides Canada catalogue.
Laboratory handling considerations
Handling of lyophilized peptide material should follow the receiving institution's validated standard operating procedures. General laboratory practice for sealed lyophilized material includes:
Note: no preparation, reconstitution, or administration instructions are provided or implied. All handling parameters must be established by qualified research personnel according to the specific experimental protocol in use.
Frequently asked questions
What is Melanotan-2?
Melanotan-2 (MT-2) is a synthetic cyclic heptapeptide analogue of alpha-melanocyte-stimulating hormone, CAS 121062-08-6, with the sequence Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH₂ and a molecular weight of 1024.18 Da. It is described in the literature as a non-selective melanocortin receptor agonist and is supplied as a lyophilized powder for in vitro laboratory research use only.
Is Melanotan-2 a cyclic peptide?
Yes. A lactam bridge between the aspartate and lysine side chains closes the sequence into a 23-membered macrocycle. This constraint holds the pharmacophore residues in a fixed conformation that the linear parent peptide cannot maintain in solution, and it is the structural feature responsible for the compound's stability relative to native α-MSH.
What is the difference between Melanotan-1 and Melanotan-2?
They are structurally different molecules with separate registry numbers. Melanotan-1 (afamelanotide, CAS 75921-69-6) is a linear 13-residue amide with a molecular weight of 1646.85 Da. Melanotan-2 (CAS 121062-08-6) is a cyclic 7-residue amide at 1024.18 Da. Their receptor profiles are described differently in the literature, and a COA quoting one registry number for the other indicates mislabelled material.
How does Melanotan-2 differ from PT-141?
PT-141 (bremelanotide, CAS 189691-06-3) is a close structural relative that differs principally in carrying a carboxy group where MT-2 carries a C-terminal amide. Their molecular weights sit roughly one dalton apart — 1024.18 Da versus 1025.16 Da — which means mass confirmation alone may not separate them without adequate instrument resolution. Registry number and chromatographic data should both be checked.
Is Melanotan-2 authorised by Health Canada?
No. Melanotan-2 is not authorised by Health Canada for human or veterinary use. It is supplied exclusively as a laboratory research chemical for in vitro and non-clinical work by qualified research personnel. It is not a drug, food, or cosmetic, and no therapeutic, clinical, or health claims are made for it.
Which melanocortin receptors does Melanotan-2 act on?
The literature describes MT-2 as a non-selective agonist at four of the five melanocortin receptor subtypes — MC1R, MC3R, MC4R and MC5R. MC2R, which responds to ACTH rather than α-MSH analogues, is not part of the described profile. This breadth is why MT-2 is commonly used as a comparator ligand in assays developing subtype-selective compounds.
Supplied as lyophilized powder with batch-specific analytical documentation, fulfilled in Canada for laboratory research use only.
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Research materials referenced on this page
The compounds compared above are stocked individually, which allows a protocol to run MT-2 against its structural relatives rather than in isolation. All are supplied as lyophilized powder with batch-specific documentation, for laboratory research use only.
Further compounds are listed across the full research catalogue.
- → PubChem CID 92432 — Melanotan II
- → PubMed — melanotan II and melanocortin receptor literature
- → Al-Obeidi et al. (1989), on conformational constraint of α-MSH analogues — PMID 2555512.
- → Chemical identifiers cross-referenced against independent peptide catalogue entries (CAS 121062-08-6).
All compounds and information referenced on this page are supplied and published exclusively for in vitro laboratory and non-clinical research use by qualified research personnel. This material is not authorised by Health Canada for human or veterinary use. No therapeutic, clinical, or cosmetic claims are made.
This material must not be administered to humans or animals. No dosage, preparation, reconstitution, or administration instructions are provided or implied. Nothing on this page is intended to diagnose, treat, cure, or prevent any disease. All handling and use must be conducted by qualified personnel in accordance with applicable institutional policies and legal requirements.
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