Chemistry and structure

A cyclic heptapeptide, a lactam ring, and a single edit that changed the drug

PT-141 is a small, rigid ring: a cyclic heptapeptide built around the alpha-MSH core residues and locked shut by a lactam bridge. Ring constraint is a standard way to buy affinity and slow degradation, though no source consulted here measures what the ring contributes in this molecule.

This unit walks the sequence, the cyclization chemistry, and the one deliberate change, an amide swapped for a free acid, that separates melanotan II from bremelanotide. No source consulted here shows that edit shifting receptor preference; the label still lists MC1R first.