PT-141 USA

PT-141 differs from Melanotan 2 by a single atom pair: an amide against a free acid at the C-terminus, one dalton on a mass spectrum. That is the whole of the structural difference, and it is the reason a PT-141 certificate needs to be read more carefully than most. This page covers the three melanocortin peptides we stock, how to confirm which one is in the vial, the one impurity class that cyclic peptides bring with them, and what ordering inside the United States involves.

The three melanocortin peptides

• Melanotan 1 (afamelanotide): a linear 13-residue alpha-MSH analog with Nle4 and D-Phe7, mass near 1,646 Da. Stocked as Melanotan 1 10 mg.
• Melanotan 2: a cyclic heptapeptide amide, Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2, mass near 1,024 Da. Stocked as Melanotan 2 10 mg.
• PT-141 (bremelanotide): the same cyclic heptapeptide with a free C-terminal acid, mass near 1,025 Da. Stocked as PT-141 10 mg.

PT-141 is the metabolite of Melanotan 2 formed by loss of the C-terminal amide. The lactam bridge between the aspartate and lysine side chains is what holds the ring closed in both. The structural comparison sets all three out, and the lactam bridge and melanocortin selectivity explains why the ring matters to receptor work. Melanocortin receptor subtypes covers the receptor family.

Confirming PT-141 against Melanotan 2

Melanotan 1 is easy to tell apart by mass. PT-141 and Melanotan 2 are not, at a glance, because 1,025 against 1,024 Da is within the rounding of a casually reported value. A certificate for either should therefore report the observed monoisotopic mass to at least one decimal place, and ideally the retention time against a reference standard, since the acid elutes differently from the amide on a reversed-phase column. Mass accuracy in ppm explains how much precision a given instrument can deliver and retention time as identity evidence covers what the second check adds.

The cyclic-peptide impurity

Cyclisation is a synthesis step, and when it is incomplete the uncyclised linear precursor remains: same sequence, mass 18 Da higher (one water), different retention time. At 99%+ purity that peak is small, but a good certificate shows that it is small rather than leaving it off. Cyclic vs linear peptides covers the chemistry. The tryptophan gives PT-141 a usable 280 nm absorbance, so a certificate run at both 220 and 280 nm should agree on the main peak; where the two disagree, something without a chromophore is co-eluting. Co-elution and what it hides is the relevant guide.

Handling

Lyophilised PT-141 is stable at minus 20 °C and tolerates ambient transit. In solution the tryptophan is light-sensitive, so stock belongs in amber or foil-wrapped tubes. The peptide is soluble in water and dilute acetic acid and less soluble near neutral pH close to its isoelectric point, which is why reconstitution in plain phosphate buffer sometimes produces haze. Isoelectric point and solubility covers the effect, and choosing a reconstitution solvent the practical options. Aliquot after reconstitution and avoid repeated freeze-thaw.

Ordering in the USA

Orders ship domestically within the United States with no import processing. USPS, UPS and FedEx services are offered at checkout, dispatch is within one business day and typical transit is two to five days. The price list puts PT-141 alongside both melanotans on one per-milligram scale, larger quantities are on the bulk orders page, and published certificates are on the certificates page.

Research use only

PT-141 from ExoLabz is a laboratory reference material for in vitro and analytical research. It is not a drug and not for human or veterinary use, and we do not provide dosing or administration information. The purity guarantee refunds the product and the cost of the test if an independent laboratory finds a vial below its stated purity.