PT-141

Chemical identity

PT-141 is the C-terminal deamidated metabolite of Melanotan II, and the structural relationship explains most of its pharmacology. Where MT-2 terminates in a primary amide, PT-141 terminates in a free carboxylic acid. That single change shifts the receptor selectivity profile and substantially reduces the melanocortin-1 activity responsible for MT-2's pigmentation effects.

The lactam bridge between the Asp and Lys side chains locks the His-D-Phe-Arg-Trp core into the conformation that the melanocortin receptors recognise. The D-phenylalanine is equally load-bearing: the L-isomer is markedly less active, so chiral purity is a genuine specification concern rather than a formality.

Mechanism in research models

PT-141 is a non-selective agonist across MC1R, MC3R and MC4R, with the MC4R interaction carrying most of the research interest. MC4R is expressed densely in the hypothalamus and the compound acts centrally rather than on peripheral vascular tissue — a distinction that separated it from the PDE5 inhibitor class during its development.

The downstream signal is cAMP accumulation through Gs coupling. Investigators running receptor assays should note the compound's activity at MC1R when interpreting results in cells expressing more than one melanocortin subtype, which is common in primary preparations.

What the literature establishes

Bremelanotide has been through a full clinical development programme and holds regulatory approval in the United States for a specific indication in premenopausal patients. That gives this compound something almost nothing else on this site has: peer-reviewed phase III efficacy and safety data at defined doses.

The most consistently reported effects in that programme were nausea, flushing and transient blood-pressure elevation — the last of these mechanistically relevant, since melanocortin agonism affects central cardiovascular regulation. Researchers designing animal protocols should account for pressor effects in their monitoring rather than treating them as incidental.

An intranasal formulation was abandoned during development specifically over blood-pressure signals at the doses required by that route. The route of administration is not a neutral variable for this molecule.

Handling, reconstitution and storage

Lyophilised material of this type is typically held at −20 °C and protected from light; confirm the validated condition on the lot documentation. The cyclic lactam structure gives PT-141 better solution stability than most linear peptides, but that is a relative statement — reconstituted material still degrades and should be treated as a short-lived reagent.

Reconstitute with bacteriostatic water for multi-use vials or sterile water where the aliquot will be consumed at once. The peptide dissolves readily; if a vial resists dissolution, suspect moisture ingress into the cake rather than applying heat or sonication.

Aliquot and freeze. Solution held at 2–8 °C should be used within the window stated on the certificate, and any solution showing haze or particulates should be discarded rather than filtered and used.

Analytical documentation

Ask for RP-HPLC purity at ≥98%, an observed mass consistent with the cyclic structure, and — for this compound specifically — confirmation of the D-Phe configuration. Chiral analysis is not standard on most peptide certificates, and the L-diastereomer is the most likely synthesis-related impurity to affect your results.

Because PT-141 and Melanotan II differ by 18 Da and share a scaffold, a mass spectrum is also the fastest way to confirm you have received the compound you ordered. Check the observed mass against the sequence rather than trusting the label.

References and authoritative sources

Chemical identity, regulatory status and anti-doping classification should be confirmed against primary sources rather than against this page. The records below are the ones to check first.

1. PubChem compound record (US National Library of Medicine)
2. PubMed indexed literature
3. DrugBank entry
4. ClinicalTrials.gov registered studies

These are database and regulatory sources. Citations to specific primary papers are being added to this page as part of ongoing scientific review; until they appear, treat the mechanism and literature sections above as a summary to verify rather than a citation of record.