PT-141 is a synthetic cyclic heptapeptide in the melanocortin family. It is structurally derived from alpha-melanocyte-stimulating hormone (α-MSH) and is closely related to melanotan II, from which it differs at the C-terminus: PT-141 ends in a free carboxylic acid where melanotan II carries an amide. Its sequence and molecular weight are listed in the chemical profile below. The compound binds several melanocortin receptor subtypes and has been examined in published in-vitro and animal research as a tool for studying melanocortin receptor signaling. This overview summarizes its chemical identity, receptor pharmacology, analytical characterization and laboratory handling. It is informational only; material described here is not intended for human use and is discussed for in-vitro laboratory research only.
PT-141 is a cyclic heptapeptide with the sequence Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH. A lactam bridge between the side chains of Asp and Lys closes the ring, which constrains the conformation of the core His-D-Phe-Arg-Trp sequence and increases resistance to proteolysis compared with linear analogs.
Molecular formula: C50H68N14O10. Molecular weight: 1,025.2 g/mol. CAS number: 189691-06-3. Classification: cyclic melanocortin receptor agonist peptide.
The D-phenylalanine in the core sequence is important for receptor affinity. The N-acetyl norleucine at the N-terminus replaces the oxidation-prone methionine of native α-MSH, removing a common source of degradation without a meaningful loss of receptor binding.
Native α-MSH is a linear 13-residue peptide derived from pro-opiomelanocortin. Medicinal-chemistry work in the 1980s truncated this sequence to its core recognition motif and introduced a side-chain lactam ring, producing cyclic analogs with much higher receptor affinity than the linear hormone. Melanotan II emerged from that series, and PT-141 is its C-terminal free-acid counterpart.
Because the two molecules share the same cyclic core, they are useful comparators in structure–activity studies that examine how the C-terminal group influences receptor subtype selectivity, binding kinetics and stability in buffer and plasma matrices.
PT-141 is a non-selective agonist of the melanocortin receptor family, with reported affinity ranked MC1R > MC4R > MC3R > MC5R > MC2R. Melanocortin receptors are class A G protein-coupled receptors that couple predominantly to Gαs, so agonist binding raises intracellular cAMP and activates protein kinase A.
In published animal research, attention has centered on MC4R expressed in hypothalamic nuclei, and PT-141 has been used as a tool compound to examine MC4R-mediated signaling in the central nervous system. In cell-based work, receptor activity is typically quantified with cAMP accumulation assays, reporter-gene assays or radioligand competition binding in cells expressing a single receptor subtype.
PT-141 has been examined in published in-vitro and animal research on melanocortin receptor pharmacology, hypothalamic peptide signaling and structure–activity relationships of cyclic α-MSH analogs. Investigators also use it as a reference ligand when characterizing new melanocortin receptor agonists and antagonists, and as a comparator for melanotan II in selectivity profiling.
Because PT-141 binds MC1R with high affinity, receptor-subtype selectivity is an important consideration in study design. Researchers commonly include subtype-selective reference ligands and receptor-null cell lines as controls so that a signal can be attributed to a specific receptor.
Identity and purity of synthetic cyclic peptides such as PT-141 are typically established by reverse-phase HPLC with UV detection, with purity reported as a peak-area percentage, and by mass spectrometry, which compares the observed mass with the calculated value of about 1,025 Da. Because the cyclization step can leave linear precursors or dimeric by-products, chromatographic resolution of these species is part of routine method development.
Form: lyophilized powder. Storage: −20°C, protected from light and moisture, in a sealed vial. Allow the vial to reach room temperature before opening to limit condensation, and avoid repeated freeze–thaw of stock material.
For research use only. Not for human consumption.
PT-141 binds all five melanocortin receptor subtypes (MC1R through MC5R), with the greatest reported affinity at MC1R and substantial activity at MC4R. These receptors couple mainly to Gαs and cAMP signaling.
Both peptides share the same cyclic lactam core, Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]. Melanotan II carries a C-terminal amide, while PT-141 has a free carboxylic acid at that position. The two are often compared in structure–activity research.
Reverse-phase HPLC is used to assess purity, and mass spectrometry confirms identity against the calculated molecular weight of about 1,025 Da. Linear precursors and dimeric by-products from the cyclization step are monitored as specific impurities.
PT-141 is not sold by Excalibur Peptides; this page is for information only. Material sold as a research chemical is supplied for in-vitro laboratory research and identification purposes only, is not approved by the FDA for human or veterinary use, and is not for human consumption.