For labs buying melanocortin peptides in Canada, this compact range covers three receptor ligands, shipped as freeze-dried powder, strictly for laboratory research use only. Subtype selectivity is the central research question for all of them, and two of the three are ring-closed (cyclic) structures.
Products at a glance
- PT-141 (bremelanotide) — cyclic; CAS 189691-06-3; approx. 1,025.2 g/mol; C50H68N14O10; sequence Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH.
- Melanotan II — cyclic amide, a near relative of PT-141; CAS 121062-08-6; approx. 1,024.2 g/mol; C50H69N15O9.
- Melanotan I (afamelanotide) — linear and considerably longer at 13 residues; CAS 75921-69-6; approx. 1,646.8 g/mol; C78H111N21O19.
PT-141 and Melanotan II sit about one mass unit apart, so on a low-resolution instrument they are the pair most likely to be mistaken for each other by mass alone. When receiving a mixed order of both, keep the vials segregated and log each against its own certificate.
Melanocortin peptides in Canada: why receptor subtype matters
There are five melanocortin receptors, MC1R to MC5R, expressed in different tissues and linked to different downstream signalling. Work with an MC1R ligand and work with an MC4R ligand address separate biology, and a compound that hits both is a blunter tool than a selective one.
Read selectivity claims closely. Because the subtypes couple differently, a ligand can show near-equal binding at two of them yet activate each with very different potency. Our pages on MC receptor subtypes and selectivity and on what Ki, IC50 and EC50 each report explain why binding ratios and functional ratios support different claims.
What ring closure means for QC
Cyclisation locks the peptide into a restricted conformation, which underlies how these ligands bind. The analytical catch is that a linear by-product with identical composition has exactly the target's mass, so a ring-opened impurity cannot be seen by mass measurement — it has to be separated on the column instead. More in cyclic and linear peptides compared.
Tryptophan and oxidation
Tryptophan appears in all three sequences, and histidine in two. Because tryptophan can oxidise, a certificate that looked clean when the lot was made says nothing definitive about material that has since been poorly stored. See how impurities form and keeping lyophilised peptides stable.
Certificates and dispatch
Products are third-party tested, published certificates appear on the COAs page as the lab supplied them, and each vial is matched to its certificate by cap and crimp colour. Orders ship as lyophilised powder from within Canada and count toward the volume tiers.
For laboratory research only — not for human or veterinary use. These materials hold no Health Canada or FDA authorisation, carry neither a DIN nor an NPN, and are not produced under pharmaceutical GMP.