Melanotan-1 vs Melanotan-2 — How They Differ
Melanotan-1 and Melanotan-2 are both synthetic analogues of α-MSH, but they are structurally distinct compounds with different CAS numbers and properties. This page sets out the factual differences.
Last updated: 2026-08-21 · By: Index Peptides technical team
| Melanotan-1 (MT-1) | Melanotan-2 (MT-2) | |
|---|---|---|
| INN / other name | Afamelanotide | — |
| Structure | Linear tridecapeptide | Cyclic heptapeptide |
| CAS number | 75921-69-6 | 121062-08-6 |
| Molecular weight | ~1646.8 g/mol | ~1024.2 g/mol |
| Derived form | [Nle4, D-Phe7]-α-MSH | Cyclic α-MSH analogue |
| Related compound | — | PT-141 is its free-acid derivative |
Linear vs cyclic
Melanotan-1 (afamelanotide) is a linear 13-amino-acid analogue of alpha-melanocyte-stimulating hormone (α-MSH) with substitutions at positions 4 and 7 that increase stability and receptor affinity. Melanotan-2 is a shorter, cyclic 7-amino-acid analogue — cyclisation through a lactam bridge constrains its shape and changes its receptor-selectivity profile.
Different chemistry
Melanotan-1 (CAS 75921-69-6, ~1646.8 g/mol) is the larger molecule; Melanotan-2 (CAS 121062-08-6, ~1024.2 g/mol) is smaller and cyclic. PT-141 (bremelanotide) is closely related to Melanotan-2 — it is the free-acid derivative in which the C-terminal amide is replaced by a carboxylic acid.
Research context
Both are tool compounds in melanocortin-receptor pharmacology — receptor-binding, subtype-selectivity and signalling studies across the MC1–MC5 receptors. The literature is preclinical and pharmacological.
Supply status
Index Peptides supplies both strictly as research chemicals for in-vitro laboratory research. Products are sold exclusively to qualified researchers and licensed laboratories. Neither is for human or veterinary use. We only answer questions about specifications, documentation and orders.
Frequently asked questions
Which is the larger molecule?
Melanotan-1 is a linear tridecapeptide of ~1646.8 g/mol; Melanotan-2 is a cyclic heptapeptide of ~1024.2 g/mol. They have different CAS numbers and are not interchangeable.
How is each batch verified?
Review the published certificate for the exact lot, including the laboratory, report date and analytical results actually reported. HPLC purity alone does not confirm LC-MS identity. Contact us before ordering if a required result is not published.
How does Melanotan-2 relate to PT-141?
PT-141 (bremelanotide) is the free-acid derivative of Melanotan-2, with a different CAS number, mass and pharmacological profile.
References
Research use only. Not for human or animal consumption.