PT-141 (bremelanotide)

Bremelanotide, widely traded as PT-141, is a cyclic seven-residue melanocortin receptor agonist. The cyclisation step is the main determinant of lot quality, and open-chain material is the impurity that most often distinguishes a cheap lot from a qualified one.

Because the molecule is a cyclic peptide, reversed-phase purity alone does not describe the lot. We ask manufacturers for the ring-opened fraction as a separately reported figure rather than folded into total impurities.

Typical related substances are the linear ring-opened precursor, D-amino acid epimers and trifluoroacetate carry-over from purification.