Catalogue / Melanotan II
Melanotan II
Also written as MT-2, MT-II.
A cyclic lactam-bridged analogue of alpha-MSH, acetylated at the N-terminus and amidated at the C-terminus.
| Molecular formula | C50H69N15O9 |
| Average mass | 1024.18 Da |
| Monoisotopic mass | 1023.5403 Da |
| Written as | Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2 |
| Class | Melanocortin analogues |
| Determination | Peptide analysis, catalogue compound |
| Price | 341 USD |
Computed at build time from the composition shown on this page, not transcribed from a supplier datasheet.
Melanotan II has an average molecular weight of 1024.18 daltons and a monoisotopic mass of 1023.5403 daltons. Identity is confirmed by matching the measured deconvoluted mass to that figure, and purity is reported separately by reversed-phase chromatography at 214 nm. The two numbers answer different questions and neither substitutes for the other.
| Written sequence | Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2 |
| Molecular formula | C50H69N15O9 |
This compound contains residues outside the standard twenty, so a theoretical mass cannot be derived from a one-letter sequence. The masses above are computed from the molecular formula instead.
This is not a technicality. A laboratory that computes an expected mass from a sequence lookup will get the wrong number for this compound, and will then either report a false mismatch or adjust the expectation to fit the measurement.
| Charge | m/z |
|---|---|
| [M+1H]+ | 1024.548 |
| [M+2H]2+ | 512.777 |
These are the ions an electrospray source is expected to produce for a neutral mass of 1023.5403 daltons, computed from the monoisotopic mass and the proton mass. They are what a raw spectrum should show before deconvolution.
A report that gives only a deconvoluted mass without the charge states it was derived from cannot be checked. Deconvolution is a calculation, and a calculation whose inputs are not shown is an assertion.
| The lactam ring closes with loss of water. The uncyclised linear precursor is eighteen daltons heavier and is the characteristic synthesis failure for this compound. |
| Melanotan II and bremelanotide differ by the C-terminal group, amide against free acid, which is roughly one dalton. Resolving that pair needs mass accuracy that a nominal-mass instrument does not have. |
| Tryptophan oxidation adds 16 daltons and is common in material stored in solution. |
Every compound fails in its own way. A generic peptide method applied without regard to these specifics produces a number that looks like a result and is not one.
Cyclic and linear analogues of alpha-MSH. Ring closure changes the mass by two daltons against the linear precursor, which is within the error of a careless measurement and not of a careful one.
LC-MS with mass accuracy sufficient to separate the cyclised product from its linear precursor, purity by RP-HPLC at 214 nm.
Where the delivered milligram figure matters rather than the percentage, net peptide content by combustion analysis and water by Karl Fischer are added, and the certificate carries a closed mass balance instead of a single purity number.
| LC-MS identity | Measured mass |
| RP-HPLC purity | Area at 214 nm |
| Net peptide content | Milligrams |
| Water content | Karl Fischer |
| Counter-ion | Ion chromatography |
| Bacterial endotoxins | USP <85> |
What is the molecular weight of Melanotan II?
The average molecular weight is 1024.18 daltons and the monoisotopic mass is 1023.5403 daltons, computed from the molecular formula C50H69N15O9 shown on this page. Both figures are calculated rather than transcribed, so they can be checked against the stated composition.
How is Melanotan II tested for purity and identity?
LC-MS with mass accuracy sufficient to separate the cyclised product from its linear precursor, purity by RP-HPLC at 214 nm. Purity describes the chromatographable fraction only and is not the same quantity as the peptide mass delivered per vial.
What goes wrong when Melanotan II is analysed?
The lactam ring closes with loss of water. The uncyclised linear precursor is eighteen daltons heavier and is the characteristic synthesis failure for this compound.
What does Melanotan II analysis cost at ANALYTON?
Peptide analysis, catalogue compound is priced at 341 US dollars, covering the determinations described on this page. Content, safety and elemental determinations are ordered alongside and are priced separately on the price list.
Other compounds in this class
Updated 2026-09-01. Masses computed at build, not transcribed.