Melanotan 2 (MT-2): identity, status and what to check

Melanotan 2 is a synthetic cyclic heptapeptide, CAS 121062-08-6, formula C50H69N15O9, calculated mass 1024.18 g/mol, closed by a lactam bridge between an aspartate and a lysine side chain. It holds no marketing authorisation in the United Kingdom or the European Union. The ring is what a certificate has to demonstrate, and a purity figure cannot.

Nomenclature: Melanotan 2, MT-II, and the number that is not a version

The same molecule is written Melanotan 2, Melanotan II, MT-2 and MT-II. The numeral is not a version number: Melanotan 1 is a different peptide with a different sequence and a different mass, and the two are not interchangeable even though listings often treat the digits as a variant. The name itself derives from melanin, and like BPC's "body protection compound" it is a label inherited from the context the sequence was studied in rather than a statement about what any vial does. Peptorium makes no claim of that kind and summarises none of the published work, which can be searched on PubMed.

In the literature the compound is classified as a melanocortin receptor ligand. That is nomenclature drawn from assay work. It describes what the molecule binds in a laboratory and says nothing about the contents of a container.

Identity: a lactam ring that mass alone will not prove

The structure is Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH₂: an acetylated N-terminus, a norleucine residue, then a ring closed by an amide bond between the aspartate side chain and the lysine side chain, and a C-terminal amide. The public record gives the formula C₅₀H₆₉N₁₅O₉ and a mass of about 1024.2: PubChem CID 92432.

Cyclisation is the analytical point. Forming the lactam ring removes a water molecule, so the cyclic peptide is 18 daltons lighter than the corresponding linear chain - which means mass spectrometry does distinguish a properly cyclised product from an uncyclised one, and that is exactly the check to ask for. What mass will not settle is the D-phenylalanine at position four: a D-residue weighs the same as its L-form, so the correct stereochemistry has to come from evidence about the synthesis rather than from the certificate. The acetyl group and the C-terminal amide are further one- and few-dalton details that a careless batch gets wrong and a measured mass catches.

Regulatory status in the UK and the European Union

Melanotan 2 holds no marketing authorisation. It is not licensed as a medicine in the United Kingdom, it is not in the EMA medicines database, and it is not an authorised cosmetic ingredient or food supplement. In the UK, regulation 46 of the Human Medicines Regulations 2012 provides that a person may not sell or supply, or offer to sell or supply, an unauthorised medicinal product, and regulation 2 defines a medicinal product by presentation as well as by function.

This compound is the clearest illustration on the site of why the presentation limb matters. A great deal of what is written about it online describes a physiological outcome in a person, and a description of that kind is capable of making an unauthorised chemical into an unauthorised medicine without a single atom changing. Nothing on this page describes any outcome in a person, and that is not squeamishness - it is the difference between a defensible page and an unlawful one.

"Research use only" is a purpose, not a permission

It states that the seller offers the material for laboratory work rather than for use in people. It is not a category in UK or EU law, not a licence, and not a review by any authority. It is not a safety claim, and it does not neutralise a claim made elsewhere on the same page.

Purity, peptide content and the ring

Purity by HPLC is the share of separated peak area belonging to the target; peptide content is the share of the vial's mass that is peptide at all, the remainder being residual water and counter-ions from synthesis and freeze-drying. Water is measured separately by Karl Fischer titration, and neither figure can be derived from the other. For a cyclic peptide the impurity most worth naming is the uncyclised linear precursor, 18 daltons heavier, and a report that lists no impurities has not shown whether it is there. The purity and peptide content guide and the certificate guide set out what a complete document contains.

What Peptorium publishes about this material

This page publishes identity: the sequence, the molecular formula and a calculated mass of 1024.18 g/mol. Each of those can be checked against a public register rather than taken on trust. Purity, peptide content and water describe one batch rather than a compound. Those figures belong on a certificate of analysis issued by the laboratory that tested that batch, and they travel with the material itself.

What to ask before buying

• Does the certificate report a measured mass beside the theoretical 1024.18 g/mol, and does it correspond to the cyclic form rather than the linear precursor 18 daltons heavier?
• Is the uncyclised precursor named in the impurity table?
• What evidence is there for the D-phenylalanine at position four? Mass will not show it.
• Is there a batch number, and a certificate for that batch alone?
• Is peptide content given separately from purity, with water by Karl Fischer?
• Are the method and the date named, and can the report be checked with the laboratory that produced it?

What is not known

• What a particular vial contains cannot be known without analysing it.
• Stereochemistry at the D-residue is not addressed by a standard certificate.
• Storage guidance for a lyophilisate is handling convention rather than a stability measurement on a given lot.

Frequently asked questions

The lyophilisate is dissolved in bacteriostatic water, and the volume of solvent fixes the concentration of the solution; the peptide calculator converts between vial content, solvent volume and concentration. No quantity is recommended for any purpose, and nothing on this site is a recommendation to use this material in humans or animals - see the research declaration.