“Cyclic” in Melanotan II describes a chemical ring formed by a bond between two amino-acid side chains. It does not mean a repeating treatment cycle, and it is not a claim that the material is safe, effective or interchangeable with another melanocortin peptide.
Melanotan II, also written Melanotan 2 or MT-II, is described in primary research as a cyclic heptapeptide analogue of alpha-melanocyte-stimulating hormone, abbreviated alpha-MSH. This guide explains the structural language a reader encounters in papers and research-product records.
Seven residues, with a ring inside the sequence
A published representation of Melanotan II is Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2. The original 1996 pilot study describes a lactam-bridged molecule and identifies its seven-residue sequence. Count the amino-acid residues: Nle, Asp, His, D-Phe, Arg, Trp and Lys.
The word “heptapeptide” refers to that count of seven. The bracketed cyclic portion contains six residues, while Nle sits outside that bracket. These statements are compatible: the molecule has seven residues in total, but the ring does not include the entire sequence.
Read the small symbols before comparing names
- Ac-: an acetyl group at the amino end, rather than an extra amino acid.
- Nle: norleucine, an amino-acid residue whose identity should not be shortened to ordinary leucine.
- D-Phe: D-phenylalanine. The D designation specifies stereochemistry and should not disappear when copying a sequence.
- cyclo[...]: a ring-forming connection within the indicated portion.
- -NH2: a terminal amide, which is part of the chemical identity.
The NIH PubChem identity record also uses a numbered representation, Ac-Nle-Asp(1)-His-D-Phe-Arg-Trp-Lys(1)-NH2. Matching markers identify the connected residues. They are not two additional residues or a concentration.
What does “lactam bridge” add?
A lactam is a cyclic amide. For Melanotan II, the relevant connection joins the Asp and Lys side chains. Counted within this seven-residue peptide, these are residues two and seven. Some papers instead retain position numbers from the alpha-MSH parent sequence, so the same positions appear as five and ten. Check which numbering convention the source uses before assuming that two descriptions disagree.
The 1989 original cyclic-lactam design study reports a family of related alpha-MSH fragment analogues. Its significance for reading a catalog is structural specificity: changing a residue or bridge can describe a different analogue, even when much of the name looks familiar. “Cyclic peptide” is a broad category, not a complete identity.
Is this just Melanotan I folded into a ring?
No. Melanotan I is a name associated with afamelanotide, a thirteen-residue alpha-MSH analogue. Melanotan II is a distinct seven-residue cyclic analogue. The afamelanotide identity record helps separate the names. A shared research family does not make them alternate labels for the same molecule.
There is also an important product distinction: FDA prescribing information for SCENESSE describes a specific afamelanotide implant. That label does not establish approval, pharmaceutical equivalence or clinical suitability for a supplier's research vial of either compound.
What a structure description cannot verify
A literature sequence describes the intended molecule. It does not show what is in a particular vial. For a laboratory purchasing record, keep the product name, lot identifier, supplied chemical form and analytical documents together. Ask which evidence addresses identity, which addresses purity and which addresses quantity; those questions should not be collapsed into one percentage.
Our guide to reading a peptide COA provides a starting point. A photograph or catalog title is useful for recognizing a listing, but neither verifies the contents or the ring-forming bond.
Find the corresponding Dissolv research listing
Dissolv lists Melanotan II 10mg for research use. The linked page is the catalog reference for this article; the title's quantity is a listing statement, not an independently verified assay result. Qualified laboratory purchasers should confirm documentation and suitability for their lawful research application before ordering.
Research use only. Not for human or veterinary use. This article provides no administration, tanning, treatment or dosing instructions. Structural terminology does not establish a safety profile.
