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 from the alpha-MSH message core and locked shut by a lactam bridge. That constraint is what gives it high potency and metabolic stability at a defined receptor.

This unit walks the sequence, the cyclization chemistry, and the one deliberate change, an amide swapped for a free acid, that turned the broad tanning peptide melanotan II into the MC4R-preferring bremelanotide.