PT-141 vs Melanotan II
Two cyclic Melanocortin peptides, side by side: how each ring is closed, the receptor selectivity that sets them apart, and what keeps each one on the bench as a reference standard.
For laboratory and research use only. The rows above describe chemistry, methods, and handling, not efficacy or any human or veterinary use. Batch documentation is available on request.
What they share
PT-141 and Melanotan II are catalogued together in the Melanocortin class, and on the bench they behave like close relatives. Both are cyclic seven-residue peptides built on the alpha-MSH scaffold, assembled by Fmoc solid-phase peptide synthesis where the chain is constructed one residue at a time on a resin, cyclized to close the ring, then cleaved, purified, and freeze-dried into a lyophilized powder.
Both are handled the same way as reference standards. Identity and purity are established with reverse-phase HPLC for the purity profile and mass spectrometry to confirm the molecular weight, and both are kept cold, dry, and dark to preserve a stable standard. Documentation describing how each batch was characterized is available on request rather than printed as a headline figure.
How they differ
The real difference is in how the ring is closed and what that does to receptor selectivity. PT-141, also known as bremelanotide, is a cyclic peptide whose ring is formed through a bridge between two residues on the alpha-MSH scaffold. Chemically it behaves as a broad melanocortin-receptor agonist, engaging the melanocortin receptor family rather than a single subtype.
Melanotan II is the same seven-residue length but is closed through a lactam (amide) bond, a different cyclization chemistry. That lactam ring constrains the backbone in a way that gives Melanotan II a more selective melanocortin profile as an alpha-MSH analog. The two therefore start from a shared scaffold but diverge at the cyclization step.
So although both are cyclic melanocortin heptapeptides made and verified the same way, their cyclization type and receptor selectivity are the core differences: a bridged cyclic broad agonist on one side, a lactam-cyclized selective alpha-MSH analog on the other. The shared "Melanocortin" grouping reflects a common scaffold, not identical chemistry.
Choosing a reference standard
Which one belongs on a given bench depends on the chemistry being referenced. A workspace studying PT-141 as a bridged cyclic broad melanocortin agonist will want it as the standard for that ring chemistry, while work centered on Melanotan II as a lactam-cyclized alpha-MSH analog calls for that selective scaffold instead. The two are complementary reference points within the melanocortin family rather than interchangeable substitutes.
In practice the pair is easy to hold together. Both are lyophilized cyclic peptides characterized by RP-HPLC and mass spectrometry and stored cold, dry, and dark, so a method built around one transfers cleanly to the other, and the two share the same handling and documentation. None of this implies any effect or use; it simply reflects how the two are catalogued, stored, and referenced as standards. Details of how identity is confirmed live in our documentation guide.
One scaffold, two ways to close the ring.
Both are cyclic seven-residue melanocortin peptides built on the alpha-MSH scaffold by Fmoc SPPS with a cyclization step.
PT-141 closes its ring through a bridge between residues; Melanotan II closes through a lactam (amide) bond.
PT-141 acts as a broad melanocortin agonist; Melanotan II has a more selective alpha-MSH profile.
Both are lyophilized, verified by RP-HPLC and MS, and stored cold, dry, and dark as reference standards.
PT-141 vs Melanotan II
What is the difference between PT-141 and Melanotan II?
Both are cyclic melanocortin peptides, but they differ in how the ring is closed and in receptor selectivity. PT-141 (bremelanotide) is a cyclic 7-residue melanocortin-receptor agonist whose ring is formed through a bridge between two residues, and it acts as a broad melanocortin agonist. Melanotan II is a cyclic lactam heptapeptide analog of alpha-MSH, closed through an amide (lactam) bond, giving it a more selective profile. The cyclization chemistry and receptor selectivity are the core differences, even though both are catalogued in the same Melanocortin class.
Are PT-141 and Melanotan II in the same class?
Yes. Both are catalogued in the Melanocortin class as cyclic melanocortin-receptor-active peptides, and both are seven-residue cyclic peptides derived from the alpha-MSH lineage, which is why they are grouped together. The shared grouping reflects a common melanocortin scaffold, not identical chemistry. You can read each compound's full chemistry in the PT-141 and Melanotan II overviews.
How are PT-141 and Melanotan II synthesized?
Both are produced by Fmoc solid-phase peptide synthesis (SPPS), assembled residue by residue on a resin, then cyclized to close the ring, cleaved, purified, and lyophilized. PT-141 is closed through a bridge between two residues, while Melanotan II is closed through a lactam (amide) bond. Identity and purity are established with reverse-phase HPLC alongside mass spectrometry, as described in our standards and verification overview.
Are PT-141 and Melanotan II for research use only?
Yes. Both are supplied as reference standards for laboratory and research use only. They are not for human or veterinary consumption, and buyers are responsible for compliance with all applicable laws and regulations.