MELANOTAN I

Description

Melanotan I is a linear 13-amino-acid peptide with a C-terminal amide and a molecular weight of 1646.85 g/mol. It is an analogue of alpha-melanocyte-stimulating hormone, and is also known as afamelanotide or NDP-MSH.

Structure and why it differs from Melanotan II

Despite the shared naming, Melanotan I and Melanotan II are structurally quite different molecules, and treating them as variants of one another is a common and consequential error.

Melanotan I keeps the full 13-residue length of native alpha-MSH and remains linear. It carries two substitutions, which is what NDP-MSH denotes: norleucine at position four in place of methionine, and D-phenylalanine at position seven in place of the L-form. The N-terminus is acetylated and the C-terminus amidated. Both substitutions resist enzymatic degradation while preserving the parent hormone’s receptor interactions.

Melanotan II, by contrast, is truncated to seven residues and cyclised through a lactam bridge, weighing 1024.18 g/mol. The two therefore differ by more than 600 daltons and by fundamental architecture: full-length linear against truncated cyclic.

Melanotan I is described in published work as showing greater relative selectivity for MC1R, the receptor subtype most associated with pigmentation, whereas Melanotan II engages melanocortin receptors broadly.

Research background

Published work has characterised receptor binding and activation in cell systems, and examined pigmentation responses 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 at position nine makes light protection worthwhile. Allow the vial to reach room temperature before opening.

Use 1646.85 g/mol for the free base; the acetate salt carries a different registry number and mass. Because Melanotan I and II are often stocked alongside one another and their names differ by a single character, confirm from the label which you are working with before calculating: the mass difference between them is large enough to make a mistake obvious only after the fact.

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

75921-69-6 (free base)

Molecular Formula

C₇₈H₁₁₁N₂₁O₁₉

Molecular Weight

1646.85 g/mol

Chain Length

13 amino acids, C-terminal amide

Sequence

Ac-Ser-Tyr-Ser-Nle-Glu-His-D-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH₂
Nle = norleucine; linear, not cyclized

Modifications

[Nle⁴, D-Phe⁷]-α-MSH

Also Known As

Afamelanotide, NDP-MSH, MT-I

Relation to MT-II

Full-length linear α-MSH analog; MT-II is a truncated cyclic analog

Physical Form

Lyophilized white powder

Storage

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

Chemical Structure