Melanotan I and Afamelanotide: When Two Names Point to the Same Peptide Sequence
Melanotan I and afamelanotide commonly refer to the same 13-residue analogue, [Nle4,D-Phe7]-α-MSH, but a name match is not the whole material record. Sequence, N-terminal acetylation, C-terminal amidation, stereochemistry, salt form, and formulation must still be checked. The approved afamelanotide implant is a specific acetate-containing formulation; that product record cannot be transferred to an unrelated research vial that shares the peptide name.
The NEXTWAVE PEPTIDES catalog entry is Melanotan I (MT-1). The melanocortin materials map places MT-1 alongside Melanotan II and bremelanotide while preserving their distinct structures.
What sequence does afamelanotide identify?
The FDA label for the approved implant describes afamelanotide as a synthetic 13-amino-acid peptide with the sequence Ac-Ser-Tyr-Ser-Nle-Glu-His-D-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH2, supplied as an acetate form within a controlled-release implant. The FDA prescribing information for SCENESSE (afamelanotide) is an authoritative formulation record for that approved product.
An earlier pharmacokinetic paper described “melanotan-I or MT-I” as [Nle4,D-Phe7]-α-MSH. The NIH PubMed: Melanotan-I pharmacokinetics study therefore supports the historical synonym relationship in its own research context. It does not make every material using MT-1 naming equivalent to the approved implant.
| Record field | Melanotan I / afamelanotide peptide | What must remain separate |
|---|---|---|
| Parent relationship | Analogue of 13-residue α-MSH | Not native α-MSH |
| Position 4 | Norleucine replaces methionine | Must not be written as the native residue |
| Position 7 | D-phenylalanine replaces L-phenylalanine | Stereochemistry is part of identity |
| N-terminus | Acetylated | Free N-terminus is a different form |
| C-terminus | Amidated | Free acid is a different form |
| Product form | May be research material or a defined formulation | An implant and a vial are not interchangeable records |
Why stereochemistry matters even when mass looks right
D-phenylalanine and L-phenylalanine have the same elemental composition and nominal mass. A basic intact-mass result can be consistent with the expected molecular mass without establishing the molecular formula or distinguishing the two configurations. The peptide stereochemistry guide explains why a matching mass must be paired with sequence history, stereochemical controls, or a suitable separation strategy.
Norleucine substitution also belongs in the sequence record. It changes the residue at position 4 without changing the peptide length. A label that states only “α-MSH analogue” omits the two substitutions that define the commonly used afamelanotide or MT-1 identity.
Structural receptor studies have compared α-MSH, afamelanotide, and other melanocortin ligands in defined receptor complexes. A NIH PubMed: MC4R ligand-recognition structure visualized ligand-receptor complexes and reported pharmacological experiments. Those results belong to the exact peptides, receptor construct, and assay conditions. They do not prove purity, formulation equivalence, or the behavior of an untested lot.
Keep MT-1 separate from MT-2 and PT-141
Melanotan II is a shorter cyclic peptide, while bremelanotide or PT-141 is a closely related cyclic record with different terminal chemistry. The Bremelanotide versus Melanotan II guide maps that distinction. Similar melanocortin naming should not override length, cyclization, termini, or stereochemistry.
For any MT-1 record, write the full sequence with Ac-, Nle, D-Phe, and -NH2 visible. Add expected formula and mass, acetate or other counterion information, water content where relevant, and the identity method. A chromatographic purity percentage should remain separate from peptide content and formulation.
Counterion reporting deserves its own line. A peptide free-base mass, an acetate-associated material, and a finished implant can share the same active peptide sequence while differing in measured mass balance and composition. The calculation should state whether it reports peptide only, salt-associated material, or the complete formulated product.
The COA library can be used to inspect reported lot fields. The Research Compounds collection and the NEXTWAVE PEPTIDES catalog provide navigation, while the exact product page and batch report define the supplied research material.
Research limitations
The FDA label defines a specific approved implant and cannot be used as evidence that a separate research product has the same formulation, release profile, regulatory status, or clinical performance. The historical study used its own material and design, and receptor structures use controlled experimental systems. This article addresses nomenclature and molecular identity only; it does not provide human-use or dosing guidance.
Frequently asked questions
Are Melanotan I and afamelanotide synonyms?
They commonly refer to the same [Nle4,D-Phe7]-α-MSH peptide sequence. The complete material and formulation still need verification.
Is Melanotan I the same as native α-MSH?
No. It substitutes norleucine at position 4 and D-phenylalanine at position 7.
Can intact mass confirm D-Phe at position 7?
Not by itself. D- and L-phenylalanine have the same mass, so stereochemical evidence requires a suitable orthogonal approach.
Does a shared peptide sequence make a research vial equivalent to the approved implant?
No. Formulation, counterion, excipients, release system, manufacturing controls, and regulatory status are separate records.