What PT-141 is
PT-141, also known as bremelanotide, is a synthetic cyclic heptapeptide with the sequence Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH. It is the C-terminal carboxylic acid analogue of MT-2, differing from it only in the replacement of the terminal amide by a free acid. The compound was first identified as a metabolite of Melanotan II and was then developed in its own right by Palatin Technologies under the code PT-141.
Like its parent it retains the His-D-Phe-Arg-Trp pharmacophore of α-melanocyte-stimulating hormone, held in a constrained conformation by the lactam bridge between the aspartate and lysine side-chains. It is an agonist at the melanocortin receptors, and the literature characterises it as having its highest affinity at MC4R and MC1R, with lower activity at MC3R and MC5R and none of consequence at MC2R. The molecular weight is approximately 1,025 g/mol and the CAS number is 189691-06-3. It belongs to the copper and melanocortin peptides class.
The published literature on the compound, with references, is collected in the monograph.
What you receive
Each vial contains PT-141 as a white lyophilised powder, sealed with a flip-off cap over a crimped stopper, in the net quantity stated on the label: 10 mg. There is no carrier, mannitol or other excipient unless the batch certificate says otherwise. The batch number is printed on the label and matches the certificate in our register.
Reading the certificate for a PT-141 batch
Purity by reversed-phase HPLC is reported as the area of the main peak against all peaks and should be above 99%. Identity by LC-MS is reported as the observed mass against the expected mass of about 1,025 Da. The point to read carefully is the distinction from MT-2: the amide and the acid differ by about 0.98 Da, which a low-resolution instrument can blur, so a good certificate either reports the accurate mass to two decimal places or notes the HPLC retention time, where the acid runs slightly earlier than the amide. Net content gives the milligrams of peptide actually present, as distinct from the nominal fill.
The usual minor impurities are the linear uncyclised peptide, which is 18 Da heavier, the des-acetyl form, 42 Da lighter, and tryptophan oxidation, 16 Da heavier. Our guide to reading a certificate of analysis walks through annotated examples, and HPLC and LC-MS explained covers the methods.
Storage and handling
Sealed vials should be kept refrigerated at 2 to 8 °C and protected from light; −20 °C is preferable beyond a few months. The cyclic structure gives PT-141 good stability as a lyophilised powder, well over a year refrigerated. The tryptophan residue is light-sensitive, so solutions belong in amber or foil-wrapped tubes. Allow the vial to reach room temperature before opening to avoid condensation on the powder. The free carboxylate makes PT-141 slightly more water-soluble than MT-2 at neutral pH; the storage and stability guide covers solvents, concentrations and freeze-thaw behaviour.