Melanotan 1 in Canada: How It Differs From Melanotan 2 and PT-141
A lab ordering Melanotan 1 in Canada often ends up with Melanotan 2 or PT-141 on the same purchase order, and that is where mix-ups begin. The three share a family name, a receptor family and in two cases almost an entire sequence, yet they are distinct molecules with different identity data. For receiving staff and QC reviewers handling several vials of each, the reliable way to keep them straight is structural: what each chain looks like, which masses to expect, and where the paperwork can mislead.
Three names that get confused on purchase orders
Most of the trouble is naming. Each compound has at least two labels in circulation, and the numbering suggests a relationship that the chemistry does not support.
- Melanotan 1 is also written Melanotan I, MT-1 or MT-I, and its nonproprietary name is afamelanotide.
- Melanotan 2 appears as Melanotan II, MT-2 or MT-II.
- PT-141 is a development code; bremelanotide is the nonproprietary name for the same molecule.
The “1” and “2” reflect the order in which the compounds were reported, not a size or strength series. It is a mistake to treat Melanotan 1 and Melanotan 2 as two grades of one product, in the way a 5mg and 10mg vial of a single compound would be.
Melanotan 1 in Canada: what the compound actually is
Melanotan 1 is a synthetic analog of alpha-melanocyte-stimulating hormone (alpha-MSH), the thirteen-residue peptide cut from the pro-opiomelanocortin precursor. It keeps the full thirteen-residue length and changes two positions: norleucine replaces methionine at position 4, and D-phenylalanine replaces L-phenylalanine at position 7. Its full notation is Ac-Ser-Tyr-Ser-Nle-Glu-His-D-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH2, sometimes written [Nle4, D-Phe7]-alpha-MSH.
Both substitutions make chemical sense to an analyst. Swapping out methionine removes the residue most prone to oxidation, so the +16 Da sulfoxide variant that complicates native alpha-MSH samples should not appear. The D-amino acid at position 7 is associated in the literature with greater resistance to enzymatic breakdown. The chain is linear, with no ring, and weighs roughly 1646.9 g/mol.
Melanotan 2 and PT-141: one functional group apart
Melanotan 2 and PT-141 are far closer to each other than either is to Melanotan 1. Both are seven-residue cyclic peptides built on the core Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]. The ring is closed by a lactam bond between the side chains of aspartate and lysine. The only structural difference is the C-terminus:
- Melanotan 2 ends in a carboxamide (-NH2).
- PT-141 ends in a free carboxylic acid (-OH).
Swapping an amide nitrogen for a hydroxyl oxygen changes the formula by one N out and one O in, and shifts the mass by just under one dalton. Melanotan 2 comes in near 1024.2 g/mol and PT-141 near 1025.2 g/mol.
Why routine mass data can miss the difference
A one-dalton gap sounds easy to measure, but it collides with natural isotopes. Every peptide of this size produces a cluster of peaks, because a fraction of its molecules carry a carbon-13 atom. The first isotope peak of Melanotan 2 sits within a few hundredths of a dalton of the main peak of PT-141. A low-resolution spectrum, or a certificate that rounds the mass to a whole number, cannot tell a pure sample of one compound from a mixture of both. High-resolution MS, or chromatographic separation before the mass measurement, is needed to settle it.
Each can appear as an impurity in the other
Because the two differ only at the C-terminus, a synthesis aimed at the amide can leave some free acid, and hydrolysis of the amide during handling can produce the acid form too. In other words, a Melanotan 2 sample can contain some PT-141 as a normal related impurity. A certificate worth relying on shows the target peak resolved from a neighbour at the adjacent mass, not simply a purity number next to a rounded molecular weight.
The ring itself is a second checkpoint. The uncyclised linear precursor is heavier than the finished ring by one water molecule (about 18 Da), and it runs at a different retention time. A clean chromatogram and a correct mass together indicate the ring closed properly.
Side-by-side specifications
| Melanotan 1 | Melanotan 2 | PT-141 | |
|---|---|---|---|
| Other names | Afamelanotide, MT-1 | MT-2, MT-II | Bremelanotide |
| Length | 13 residues | 7 residues | 7 residues |
| Shape | Linear | Cyclic (lactam) | Cyclic (lactam) |
| C-terminus | Amide | Amide | Free acid |
| Molecular formula | C78H111N21O19 | C50H69N15O9 | C50H68N14O10 |
| Approx. molecular weight | 1646.9 | 1024.2 | 1025.2 |
| CAS number | 75921-69-6 | 121062-08-6 | 189691-06-3 |
When a name on a label and a number on a certificate disagree, trust the formula, mass and CAS number, in that order of usefulness, over the product name.
Receptor-level differences in the literature
All three act at melanocortin receptors, a family of five G protein-coupled receptors labelled MC1R to MC5R. Their receptor profiles are one reason researchers choose between them.
- Melanotan 1 is described in receptor studies mainly as a potent MC1R agonist, reflecting its close resemblance to alpha-MSH.
- Melanotan 2 is broadly non-selective across MC1R, MC3R, MC4R and MC5R in binding and functional assays.
- PT-141 shares that core and a similar spread, with the literature usually focusing on its activity at MC3R and MC4R.
None of the three is a meaningful ligand at MC2R, which responds to ACTH. For a closer look at how the ring and the terminal group relate to selectivity, see our article on PT-141 and the lactam bridge.
Receiving all three in one order
These are three white lyophilised powders, and two of them are nearly impossible to tell apart without instruments. When a multi-vial shipment includes more than one of them, a few habits prevent errors that are expensive to unwind later:
- Sort vials by compound before they reach the cold room, and store each compound in its own labelled container.
- Match each vial’s cap and crimp colour to the certificate you are filing it under, rather than relying on the printed name.
- Record the formula and mass from the certificate in your inventory log next to the lot, so a future user checks against numbers rather than names.
- Be wary of any certificate that reports only a whole-number mass for Melanotan 2 or PT-141.
We stock Melanotan 1, Melanotan 2 and PT-141 in 10mg vials, shipped from within Canada. Mix-and-match volume pricing means all three count toward the same break. Our products are third-party tested for purity by HPLC, and certificates are published for some products on the certificates of analysis page.
These melanocortin peptides are sold by Bulk Peptides solely for in-vitro laboratory research. Human and veterinary use are excluded, and nothing here should be read as information about use in people.
