PT-141: A Research Primer

PT-141 is a synthetic cyclic peptide catalogued under the name Bremelanotide. It belongs to the melanocortin family and is structurally a cyclic analog of alpha-melanocyte-stimulating hormone (alpha-MSH), one of the body's natural melanocortin peptides.

What PT-141 is

PT-141 is a cyclic heptapeptide, meaning seven amino-acid residues joined into a closed ring rather than a straight chain. The ring is formed by a lactam bridge, an amide bond that links the side chain of an aspartate residue to the side chain of a lysine residue, and the N-terminus carries an acetyl group. That ring is what separates it from an ordinary linear peptide of the same length.

It is fully synthetic. Chemists assemble the seven residues and close the ring; nothing is extracted from tissue. The molecule is closely related to Melanotan II, another cyclic melanocortin peptide, and the two differ chiefly at the C-terminus, where PT-141 carries a carboxylic acid and Melanotan II carries an amide. Because of that lineage you will sometimes see PT-141 described as a metabolite of Melanotan II. Within the ring sits the His-D-Phe-Arg-Trp motif, the core sequence that melanocortin analogs share with the parent hormone, and it is the part chemists preserve when they build these cyclic peptides. In catalogues and the literature the molecule is grouped as a cyclic melanocortin-receptor peptide.

The chemistry

These are the identifiers that fix which molecule is in the vial, independent of whatever trade name a supplier prints on the label.

• CAS number: 189691-06-3
• Molecular formula: C50H68N14O10
• Molecular weight: 1025.18 g/mol
• Sequence: Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH (lactam-cyclized)
• Class: cyclic heptapeptide, melanocortin family, analog of alpha-MSH
• Other names: Bremelanotide, PT141

Two of the sequence elements repay a closer look. "Nle" is norleucine, a non-standard amino acid, and "D-Phe" is the D-enantiomer of phenylalanine rather than the usual L-form. Both are deliberate substitutions, and both are why the one-letter shorthand used for ordinary peptides does not cleanly represent this one. When you check a certificate, match the CAS number first; it is the identifier that does not vary between sources or survive a transcription slip. A mass-spectrometry figure for the intact molecule should land close to 1025 g/mol, and a number well off that points to the wrong species or a fragment rather than to anything about the label.

Where it appears in the research literature

PT-141 shows up mainly in melanocortin-system research, the field concerned with the melanocortin receptor subtypes, catalogued MC1R through MC5R, and with how peptide ligands bind to them. Groups working in peptide pharmacology and receptor-binding studies reference it as a cyclic melanocortin-receptor ligand.

Those are subject areas, not conclusions. Naming the field a compound turns up in says what researchers have looked at, not what they reported. If you want the underlying papers, the CAS number and the sequence above are the search terms that pull them up faster than any product name.

How it is supplied and handled

PT-141 is supplied as a lyophilized solid, freeze-dried into a dry cake, stored cold and kept out of light. Store the vial at -20 degrees C and protect it from light. A dry peptide handles transit and time far better than a solution does, which is the reason it ships in that form.

Keep the vial sealed until you are working with it, and limit its exposure to moisture and repeated temperature swings. As with most lyophilized peptides, the vial may hold a bulking agent so there is visible material to work with, and a proper certificate accounts for that filler when it reports mass.

How the lots are tested

The two measurements that matter for a peptide are identity and purity. Mass spectrometry confirms the molecule matches the label, and HPLC measures how much of the sample is the target peptide against related impurities, read at 220 nm, the standard wavelength for the peptide bond.

Kits Peptides has each lot it stocks tested by an independent third-party laboratory before it reaches the shelf. If you have not worked through one of these documents before, there is a walkthrough on [how to read a peptide COA](/research/how-to-read-a-peptide-coa), and a broader [checklist for sourcing research peptides in Canada](/research/buying-research-peptides-canada) covers what else to verify before ordering. The product listing itself is at [PT-141](/products/pt-141). Orders leave Vancouver, BC with tracking and reach research customers across Canada.

*All products are supplied as laboratory reagents for research use only. Not for human or veterinary use.*