PT-141

Description

PT-141 is a cyclic heptapeptide with the sequence Ac-Nle-cyclo(Asp-His-D-Phe-Arg-Trp-Lys)-OH and a molecular weight of 1025.16 g/mol. It is a melanocortin receptor agonist, also known as bremelanotide, and is a metabolite-derived analogue of Melanotan II.

Structure and the difference from Melanotan II

PT-141 and Melanotan II share the same seven residues, the same norleucine substitution, the same D-phenylalanine, and the same lactam bridge between positions two and seven. The single structural difference is at the C-terminus: PT-141 carries a free carboxylic acid where Melanotan II carries an amide.

The molecules therefore differ by one dalton, 1025.16 against 1024.18. That is close enough that mass alone is a poor way to distinguish them, and researchers should rely on the label and certificate rather than analytical mass when identifying which compound is in hand.

The origin of PT-141 is worth knowing: it was identified as a metabolite of Melanotan II rather than designed from scratch. Loss of the terminal amide in vivo produces the free acid, and that breakdown product turned out to have a receptor profile distinct enough to warrant separate investigation.

Receptor profile

The amide-to-acid change shifts selectivity. Melanotan II is described in published work as broadly non-selective across melanocortin receptor subtypes. PT-141 is described as showing greater relative activity at MC4R and MC3R, with reduced activity at MC1R, the subtype most associated with pigmentation.

That difference is the entire reason both compounds exist as separate research materials, and it is a useful illustration of how a minimal terminal modification can redirect a peptide’s receptor preference.

Research background

Published work has characterised binding and activation across melanocortin receptor subtypes in cell systems, and examined central melanocortin signalling in animal models.

The material supplied here is for laboratory research only and is not intended for human or veterinary use.

Storage and handling

Store the lyophilized powder at 36 to 46 °F (2 to 8 °C), desiccated and protected from light. The tryptophan residue makes light protection worthwhile. Allow the vial to reach room temperature before opening.

Use 1025.16 g/mol for the free base. Acetate salt forms carry a different mass, commonly around 1085 g/mol; check your lot certificate.

Purity and verification

Each lot is analysed by an independent laboratory, with identity confirmed by mass spectrometry and purity by HPLC. Test scope varies by lot; consult the certificate for the lot you receive.

Compound Identity

CAS Number

189691-06-3 (free base)

Molecular Formula

C₅₀H₆₈N₁₄O₁₀

Molecular Weight

1025.16 g/mol

Chain Length

7 amino acids, cyclic lactam

Sequence

Ac-Nle-cyclo(Asp-His-D-Phe-Arg-Trp-Lys)-OH
Nle = norleucine; (2→7) side-chain lactam bridge

Also Known As

Bremelanotide

Relation to MT-II

C-terminal free acid analog of Melanotan II

Physical Form

Lyophilized white to off-white powder

Storage

36–46 °F (2–8 °C), desiccated and protected from light

Chemical Structure