Research area

Melanocortin peptides

Melanocortin peptides are analogues of α-melanocyte-stimulating hormone (α-MSH) that act on the melanocortin receptors MC1R to MC5R; Melanotan I, Melanotan II and PT-141 are the members listed by Vesta.

All three share the His-Phe-Arg-Trp core that melanocortin receptors recognise. Melanotan I (afamelanotide) is a linear 13-residue analogue. Melanotan II and PT-141 (bremelanotide) are cyclic heptapeptides closed by a lactam bridge between aspartic acid and lysine, and they differ only at the C-terminus: an amide in Melanotan II and a free acid in PT-141.

In the laboratory they are used as reference agonists for the different melanocortin receptor subtypes. Medicinal chemistry papers use Melanotan II as a template for finding functionally selective agonists.

Compounds in this group

Compound	Type	Formula	Average mass (g/mol)	Listings
Melanotan I	Peptide	C₇₈H₁₁₁N₂₁O₁₉	1646.85	1
Melanotan II	Peptide	C₅₀H₆₉N₁₅O₉	1024.18	1
PT-141	Peptide	C₅₀H₆₈N₁₄O₁₀	1025.16	1

Analytical points for this group

Melanotan II and PT-141 differ by only 0.984 Da; a mass spectrum should be read with at least that resolution in mind.
A cyclic peptide has an open-chain impurity 18.011 Da heavier if ring closure was incomplete.
Melanotan I (about 1646.8 Da) and Melanotan II (about 1024.2 Da) are easy to tell apart by mass; Vesta lists a single product called Melanotan I/II, so check which was supplied.
Tryptophan is the main oxidation site; norleucine replaces the oxidation-prone methionine of α-MSH.

Guides

GuideMass Spectrometry for Peptide Identity: A Practical Guide

How expected mass, observed ions, charge states, adducts, and deconvolution support peptide identity without being confused with purity.

ExplainerPeptide Sequence Notation Explained: One-Letter Codes, D-Amino Acids and Terminal Groups

How to read peptide names such as Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2, and what the brackets, prefixes and suffixes mean for the mass.

GuideCommon Peptide Degradation Products and the Mass Shifts That Reveal Them

Oxidation, deamidation, disulfide changes, pyroglutamate formation and adducts each leave a characteristic mass difference. Learn the numbers and…

Frequently asked questions

Which compounds are in the melanocortin peptides group?

Melanotan I, Melanotan II, PT-141.

How should a batch of a melanocortin peptides compound be checked?

Melanotan II and PT-141 differ by only 0.984 Da; a mass spectrum should be read with at least that resolution in mind. A cyclic peptide has an open-chain impurity 18.011 Da heavier if ring closure was incomplete.

Other research areas

All compound references →