MELANOTAN II

Description

Melanotan II is a cyclic heptapeptide with the sequence Ac-Nle-cyclo(Asp-His-D-Phe-Arg-Trp-Lys)-NH₂ and a molecular weight of 1024.18 g/mol. It is a synthetic analogue of alpha-melanocyte-stimulating hormone and a non-selective melanocortin receptor agonist.

Structure

Two engineering decisions define this molecule.

The first is truncation. Native alpha-MSH is 13 residues; Melanotan II reproduces only the core message sequence in seven, with norleucine substituted for methionine at the first position and D-phenylalanine replacing the natural L-form.

The second is cyclisation. A lactam bridge connects the side chains of the aspartate at position two and the lysine at position seven, closing the peptide into a ring. This constrains the molecule into a conformation resembling the receptor-bound shape of the parent hormone, which both increases binding and substantially reduces susceptibility to peptidases, since a cyclic backbone presents no free ends for exopeptidases to attack.

Relationship to PT-141 and Melanotan I

These three products derive from the same parent hormone and are frequently confused, so the distinctions are worth stating precisely.

PT-141 is nearly identical to Melanotan II. Same seven residues, same lactam bridge, same core. The only difference is the C-terminus: PT-141 terminates in a free acid, Melanotan II in an amide. One dalton apart in formula, 1025.16 against 1024.18. That small change alters receptor selectivity, which is why they are studied separately.

Melanotan I, despite the shared name, is structurally quite different. It is a full 13-residue linear analogue at 1646.85 g/mol, not a truncated cyclic one. Sixty percent heavier and a different molecular architecture entirely.

KPV, also in this catalogue, takes the opposite approach: it is the three-residue tail of alpha-MSH, retaining inflammatory signalling while discarding pigmentary activity.

Research background

Published work has characterised binding and activation across the melanocortin receptor subtypes, where Melanotan II is described as non-selective, engaging several including MC1R and MC4R. This lack of selectivity is the defining feature of its research profile and the reason more selective analogues were subsequently developed.

Further published work has examined pigmentation responses in animal models, and behavioural studies have investigated melanocortin signalling in the central nervous system.

No regulatory authority has approved Melanotan II for any use. The material supplied here is for laboratory research only.

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 1024.18 g/mol for the free base, and note that acetate salt forms carry a different mass. Given the one-dalton difference from PT-141, confirm from the label and certificate which compound you are working with rather than relying on mass alone.

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

121062-08-6 (free base)

Molecular Formula

C₅₀H₆₉N₁₅O₉

Molecular Weight

1024.18 g/mol

PubChem CID

92432

Chain Length

7 amino acids, cyclic lactam

Sequence

Ac-Nle-cyclo(Asp-His-D-Phe-Arg-Trp-Lys)-NH₂
Nle = norleucine; (2→7) side-chain lactam bridge

Also Known As

MT-II, MTII

Physical Form

Lyophilized white to off-white powder

Storage

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

Chemical Structure