BULKGLP RESEARCH LIBRARY
Melanotan II: cyclic structure and chemical reference
Published
Melanotan II reference identity
Melanotan II, also written Melanotan 2 or MT-II, is a synthetic cyclic heptapeptide associated with melanocortin research. Its seven-residue structure includes norleucine and D-phenylalanine, an acetylated amino terminus and an amidated carboxyl terminus. The cyclic linkage joins an aspartate side-chain carboxyl group to the lysine side-chain amino group. These modifications distinguish the reference molecule from a simple unmodified linear amino acid chain.
The condensed notation Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2 retains the nonstandard residue, stereochemistry, terminal groups and ring. PubChem's shorter sequence field is not a complete substitute for that structural description. Melanotan I and other related melanocortin analogues have separate molecular identities; a similar name does not make their formulas, masses or reference data interchangeable.
| Reference compound | Melanotan II; MT-II; cyclic heptapeptide |
|---|---|
| Parent CAS registry number | 121062-08-6 |
| Parent molecular formula | C50H69N15O9 |
| Parent molecular weight | 1024.2 g/mol (PubChem average molecular weight) |
| Condensed structure | Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2 |
| Ring connection | Asp-Lys side-chain lactam; amino-acid positions 2 to 7 |
| Supplied salt and hydration | Not established by the parent structure; consult lot-specific documentation |
Why topology matters in the literature
The original design work by Al-Obeidi and colleagues studied cyclic lactam analogues of alpha-melanotropin. A later preparative synthesis paper by Ryakhovsky and colleagues documents construction of Melanotan II in solution, including formation of the lactam and addition of the acetylated norleucine unit. These are useful primary sources for the molecule's architecture and synthetic identity.
Ring formation restricts the connectivity of the peptide; it is part of what must be identified, rather than a packaging attribute. When reading structure-activity work, keep the exact analogue, residue substitutions and assay system attached to its results. Findings for a family of melanocortin analogues are not a certificate for another preparation or a guarantee of an outcome.
Analytical interpretation for a cyclic peptide
An intact mass measurement can help distinguish the intended parent mass from major truncations or a different compound. It cannot alone prove the intended side-chain ring connection, the position of every residue or D/L configuration. A useful identity assessment explains how the reported methods address those features, with suitable reference comparisons or additional structural data where needed.
For chromatography, inspect the separation method, detection conditions and integration basis. A main-peak area percentage describes the chromatogram produced by that method. It does not independently establish the quantity of peptide in a vial, the counterion content or the chemical identity of every co-eluting species. Quantitative content and structural identity should therefore be evaluated as distinct measurements.
For method comparison, retain the exact reference structure and reporting convention alongside the result. A database drawing, a chromatographic retention time and a molecular ion are different forms of evidence. Agreement among appropriate independent observations is more informative than repeating the same unqualified identity label across several report fields.
Vial format and laboratory records
The catalog identifies a nominal 10 mg research vial. The molecular formula above describes the parent molecule, excluding any accompanying counterions and residual water. Keep the nominal label separate from measured content and clarify whether an assay result uses an as-received, salt or peptide basis.
Match documentation to the received lot and record storage requirements, receipt condition and analytical sample history. Do not assign an expiry or solution stability from a study performed under different conditions. Materials on this listing are for laboratory research only. This page contains chemical reference information rather than human-use or preparation guidance.
Frequently asked questions
Is Melanotan II the same chemical as Melanotan I?
No. They are distinct structures. Reference identifiers and analytical comparisons must match the compound actually specified.
Does a correct molecular mass prove the cyclic structure?
No. Intact mass is one identity observation. Connectivity, ring closure and stereochemistry can require additional evidence beyond that number.
Primary sources and chemical records
- PubChem: Melanotan II, CID 92432
- Al-Obeidi et al.: design of cyclic lactam alpha-melanotropin analogues (1989)
- Preparative solution-phase synthesis of Melanotan II (2008)
- USP researchers: reference standards and quality characterization of synthetic peptides (2023)
Prepared by BulkGLP. Editorial review: 2026-11-04.