PT-141

Research Context

PT-141 is a synthetic cyclic heptapeptide analogue of α-melanocyte-stimulating hormone (α-MSH), the endogenous ligand of the melanocortin receptor family. It was designed as a conformationally constrained version of the α-MSH core sequence: where the natural hormone is an open chain, PT-141 closes part of that chain into a ring, which limits the backbone to a narrower set of shapes.

Preclinical studies have examined PT-141 in cell-based assay systems, including work on melanocortin receptor binding profiles.

Chemistry & Structural Modification

PT-141, also designated bremelanotide, is a cyclic heptapeptide. Its N-terminus is acetylated rather than free, a standard modification for melanocortin analogues because it blocks aminopeptidase degradation, and its ring is closed by a lactam bridge between the aspartic acid side chain and the lysine side chain. The backbone is therefore a macrocycle rather than an open chain, with the C-terminal carboxylic acid sitting outside the ring.

Two of the seven residues are not standard proteinogenic L-amino acids: norleucine (Nle), a straight-chain isomer of leucine, and D-phenylalanine, the D-enantiomer of phenylalanine. The His-D-Phe-Arg-Trp run within the ring is the conserved melanocortin core, the same motif carried by α-MSH and by Melanotan-1.

• Sequence: Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH (7 residues)
• Molecular formula: C₅₀H₆₈N₁₄O₁₀
• Molecular weight: 1025.18 g/mol
• CAS number: 189691-06-3; PubChem CID 9941379

Lyophilisation & Stability

PT-141 is supplied as a lyophilised powder. Lyophilisation removes residual moisture that would otherwise promote slow peptide-bond hydrolysis during long-term storage. This sequence contains tryptophan, which is both oxidation-prone and light-sensitive, so keeping the vial dark is a specific requirement for this peptide and not a generic precaution.

Storage

Store lyophilised vial at 2 to 8°C, protected from light. (Long-term storage at −20°C is standard practice.)

Reconstituted solution: 2 to 8°C, used within 14 to 30 days. Avoid repeated freeze–thaw cycles.

Quality & Documentation

• Purity: ≥99% by HPLC
• Certificate of Analysis (COA): published on our COA page.