Catalogue / PT-141
PT-141
Also written as Bremelanotide.
The C-terminal free acid metabolite of melanotan II, differing from it by a single dalton and sold as a distinct product.
| Molecular formula | C50H68N14O10 |
| Average mass | 1025.16 Da |
| Monoisotopic mass | 1024.5243 Da |
| Written as | Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH |
| 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.
PT-141 has an average molecular weight of 1025.16 daltons and a monoisotopic mass of 1024.5243 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]-OH |
| Molecular formula | C50H68N14O10 |
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]+ | 1025.532 |
| [M+2H]2+ | 513.269 |
These are the ions an electrospray source is expected to produce for a neutral mass of 1024.5243 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.
| One dalton separates this compound from melanotan II. It is the clearest case in the peptide market where nominal-mass identification is not identification. |
| Because the difference is a deamidation, a batch of melanotan II stored in aqueous solution will slowly generate this compound, and vice versa is not possible. |
| Both compounds share retention behaviour closely enough that chromatography alone cannot assign which is in the vial. |
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 PT-141?
The average molecular weight is 1025.16 daltons and the monoisotopic mass is 1024.5243 daltons, computed from the molecular formula C50H68N14O10 shown on this page. Both figures are calculated rather than transcribed, so they can be checked against the stated composition.
How is PT-141 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 PT-141 is analysed?
One dalton separates this compound from melanotan II. It is the clearest case in the peptide market where nominal-mass identification is not identification.
What does PT-141 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.