MSH analogues are synthetic peptides derived from α-MSH, a 13-residue tridecapeptide with an N-terminal acetyl group and a C-terminal amide. The compounds listed here include linear analogues carrying a norleucine-for-methionine and a D-phenylalanine-for-L-phenylalanine substitution, and cyclic heptapeptide analogues closed by a lactam bridge between an aspartate and a lysine side chain. The cyclic members therefore have no free C-terminus and give a single dominant mass in electrospray analysis. Each compound is supplied as a lyophilized powder in a sealed vial; the product page states whether the listed molecular weight refers to the free peptide or to a specified salt.
Listed here: Melanotan-I, Melanotan-II, PT-141 (10mg). Each product page lists the CAS number, molecular formula, molecular weight and, for peptides, the amino-acid sequence. Reported HPLC purity is shown per product; the HPLC and mass-spectrometry identity report is sent by email on request, before you order if you want to see it first.
Guides: PT-141 (Bremelanotide): Cyclic Structure, CAS Records, Salt Form and Expected Mass · Melanotan-II (MT-II): Cyclic Lactam Structure, Sequence, CAS 121062-08-6 and Salt Form
Frequently asked questions
Which MSH analogues does Pepta Labs list?
This category currently lists 3 compounds: Melanotan-I, Melanotan-II and PT-141, each supplied as lyophilized powder in a sealed vial at the nominal quantity printed on the label. Each product page states the CAS number, molecular formula, average molecular weight and sequence, the reported HPLC purity for the listing and, where a verified record exists, the structural class, residue count and typical salt form, and whether the listed molecular weight refers to the free peptide or to a specified salt.
What is an MSH analogue, chemically?
A synthetic peptide derived from α-MSH, a 13-residue tridecapeptide with an N-terminal acetyl group and a C-terminal amide. The linear analogues keep the 13-residue length and carry a norleucine-for-methionine substitution at position 4 and a D-phenylalanine at position 7. The cyclic analogues are heptapeptides closed by a lactam bridge between an aspartate side chain at position 2 and a lysine side chain at position 7, with an N-acetyl norleucine at the N-terminus; one ends in a C-terminal amide and one in a free carboxylic acid.
How do Melanotan-II and PT-141 differ chemically?
They share the same seven-residue ring and lactam bridge; Melanotan-II ends in a C-terminal amide and PT-141 in a free carboxylic acid. Replacing the amide with a hydroxyl adds about 1 Da, so their average molecular weights are 1024.18 Da and 1025.17 Da, and the expected mass on a report differs by that amount. Because the ring closes the side chains, each gives a single dominant mass in electrospray analysis. The Melanotan-II guide and the PT-141 guide give the calculated masses, CAS records and salt forms.