# PT-141 Spray

> Research use only. Not for human or veterinary use. Supplied by Veracue Labs.

- Page: https://veracuelabs.com/product/pt-141-spray
- Category: Nasal Sprays
- Sizes and prices in USD: 10 mg at $82.49
- Certificate of analysis: none posted on the page. Request one for a specific lot at https://veracuelabs.com/contact-us.
- Prices are a snapshot from 2026-10-17. The product page shows the current price.

## Overview

PT-141 Spray is a spray-dispensed research bottle of a seven-residue cyclic peptide: an acetylated norleucine followed by a ring of Asp, His, D-Phe, Arg, Trp and Lys, closed by an amide bond between the Asp and Lys side chains and ending in a free carboxylic acid. Reference values for the free peptide are C50H68N14O10, an average mass near 1025.2 g/mol and CAS 189691-06-3. That acid terminus is what separates it from Melanotan II, which carries an amide and weighs about one unit less.

## Product Details

### PT-141 Spray: Compound Summary

PT-141 is a seven-residue cyclic peptide. An acetyl cap sits on the N-terminal norleucine, and the segment that follows (Asp, His, D-Phe, Arg, Trp, Lys) is folded into a ring by an amide bond running from the aspartic acid side chain to the lysine side chain. The chain finishes with a free carboxylic acid. For the free peptide the reference formula is C50H68N14O10, the average mass is about 1025.2 g/mol and the monoisotopic mass is 1024.52428442 Da.

Veracue supplies PT-141 as a spray-dispensed 10 mg bottle with 45 sprays per bottle, for laboratory research only.

### Specifications

Product: PT-141 Spray (compound also written PT141)
Structure class: Cyclic heptapeptide with a side-chain lactam bridge from Asp to Lys
Sequence: Ac-Nle-cyclo(Asp-His-D-Phe-Arg-Trp-Lys)-OH
Molecular formula (free peptide): C50H68N14O10
Average molecular weight: About 1025.2 g/mol
Monoisotopic mass: 1024.52428442 Da
CAS Registry Number: 189691-06-3
PubChem CID: 9941379
Size offered: 10 mg
Sprays per bottle: 45
Packaging: Spray-dispensed bottle
Research designation: Research Use Only

The identity rows describe the free peptide as a reference molecule, not a Veracue lot result. Salt or counterion form, purity and other lot-level details are reported on the documentation for a given lot, which can be requested through the contact page.

### Compounds Easily Mistaken for PT-141

- Melanotan II. It has the same ring and the same first residue but ends in a C-terminal amide instead of a free acid, so its formula (C50H69N15O9) and CAS number (121062-08-6) are different.
- Disulfide-ring peptides. PT-141 contains no cysteine, and its ring is held by an amide bond rather than an S-S bond.
- The open-chain form of the same sequence. If the ring has not been closed, the molecule is heavier by one water.
- Anything identified only by a nickname or by the one-letter string XDHFRWK, which drops the acetyl cap, the D-configuration and the ring.

## Research Focus & Mechanism Overview

### Reading the Structure, Feature by Feature

Feature: Where it sits: Why it matters for identity

Acetyl cap: N-terminal amine of norleucine: Blocks the free N-terminal amine, which is one reason a bare residue string undersells the molecule.
Norleucine (Nle): Position 1, outside the ring: A non-proteinogenic residue with the same elemental composition as leucine and isoleucine.
Aspartic acid: Position 2, inside the ring: Its side-chain carboxyl supplies the carbonyl of the lactam bond.
His, D-Phe, Arg, Trp: Positions 3 to 6, inside the ring: The His-Phe-Arg-Trp stretch echoes the core of α-MSH, but the phenylalanine is the D-enantiomer.
Lysine: Position 7, ring closure: Its side-chain amine supplies the nitrogen of the lactam bond, while its own carboxyl stays free as the C-terminus.
Free carboxylic acid: C-terminus: The single point of difference from Melanotan II, which has an amide at this position.

Some databases write the same structure with numbered ring-closure labels, as Ac-Nle-Asp(1)-His-D-Phe-Arg-Trp-Lys(1)-OH, where the two (1) markers flag the residues joined by the lactam bond. It is the same molecule as the cyclo(...) form used above.

### A Lactam Ring Is Not a Disulfide Ring

A lactam bridge forms when a side-chain carboxyl and a side-chain amine condense into an amide bond, releasing one molecule of water. That makes the ring-closed peptide about 18 Da lighter than its open-chain form, a gap that mass spectrometry resolves easily. No sulfur is involved, so there is no cysteine and no S-S bond to look for in a PT-141 sample.

### Structural Comparison With Melanotan II

Attribute: PT-141: Melanotan II

Shared core: Ac-Nle-cyclo(Asp-His-D-Phe-Arg-Trp-Lys): Same core
C-terminus: Free carboxylic acid (-OH): Amide (-NH2)
Molecular formula: C50H68N14O10: C50H69N15O9
Average mass: About 1025.2 g/mol: About 1024.2 g/mol
Monoisotopic mass: 1024.52428442 Da: About 1023.5403 Da
CAS Registry Number: 189691-06-3: 121062-08-6

Trading a terminal amide for an acid replaces a nitrogen-bearing group with an oxygen-bearing one, and that swap accounts for every difference in the table. The comparison is structural only and does not rank the two compounds.

### Melanocortin Receptors in Assay Systems

The melanocortin receptors, MC1R through MC5R, are G protein-coupled receptors, and α-MSH is their prototype peptide ligand. In cell-based binding and signaling assays, PT-141 is described as a non-selective agonist with activity at MC1R, MC3R and MC4R.

That description belongs to the assay. Potency and affinity values shift with the cell line, the species and the readout, so none are quoted here, and activity at a receptor in a dish does not establish what that receptor does inside an intact organism.

### Naming the Compound in a Methods Section

Supplier naming is not uniform, and PT-141 and PT141 are simply two spellings of one name. A methods section is stronger when the name is paired with the sequence or the CAS number, 189691-06-3, and with the lot number of the material actually used. Veracue provides no dosing, administration or usage guidance of any kind, and the information here is limited to molecular reference data and analytical context.

## Quality & Purity Standards

### Verifying PT-141 by Mass Spectrometry

A mass spectrometer reports mass-to-charge ratio (m/z), not molecular weight. For a peptide of this size in electrospray, the singly and doubly protonated ions are the ones to look for. Calculated from the monoisotopic mass, they fall near 1025.532 for [M+H]+ and 513.269 for [M+2H]2+.

Species: Neutral monoisotopic mass: [M+H]+: [M+2H]2+

PT-141 (free peptide): 1024.5243: 1025.5316: 513.2694
Melanotan II (free peptide): 1023.5403: 1024.5475: 512.7774
PT-141 sequence with the ring left open (adds one water): 1042.5348: 1043.5421: 522.2747

Values are calculated from the formulas, not measured on a Veracue lot. On a low-resolution reading the first two rows are easy to blur: the first 13C isotope peak of Melanotan II’s [M+H]+ ion sits only about 0.02 m/z above the monoisotopic [M+H]+ ion of PT-141. Resolving power, not just a rounded mass, decides whether a spectrum separates them.

### Four Differences a Single Number May Not Settle

- Acid versus amide: the neutral masses are 1024.52 and 1023.54, so the resolution used matters. Fragment ions that contain the C-terminus shift by 0.984 Da between the two.
- Norleucine versus leucine or isoleucine: the composition is identical, so an accurate-mass match alone cannot rule out a swap. A reference standard or other independent evidence is needed.
- D-phenylalanine versus L-phenylalanine: the masses are identical, and mass spectrometry cannot show the configuration on its own.
- Ring closed versus open: the open form is about 18 Da heavier, which a mass reading separates clearly.

### What Each Technique Can and Cannot Show

Technique: What it reports: What it cannot settle alone

RP-HPLC: Chromatographic purity as a peak-area share: Which compound the main peak is
High-resolution MS: Accurate mass to compare with the calculated values above: Residue order and stereochemistry
Tandem MS: Fragment ions that support the sequence and the terminus: Quantity or purity
Amino acid analysis: Residue composition and net peptide content: Residue order, and whether the ring is closed
Chiral analysis or reference-standard comparison: Whether the phenylalanine is D or L: Purity of the rest of the sample

### Reading the Paperwork for a Spray-Dispensed Bottle

A certificate describes one lot. Check that its lot number matches the bottle you received, then look for the compound name, test date, testing laboratory, named methods and, where mass spectrometry was run, the observed and expected masses with the ion and charge state stated. The label on Veracue’s bottle gives the compound name, the 10 mg strength and a research-purposes-only statement.

Published lot records are listed in the certificate library. If the PT-141 lot you hold is not there, ask for its documentation through the contact page, and include any figure you need stated in writing, such as concentration.

## Compliance Notice

### Research Use Only

PT-141 Spray is sold for laboratory research and analytical work only. It is not for human or veterinary use, and it is not a drug, cosmetic, supplement or food. Veracue provides no dosing, administration or usage guidance of any kind for this or any other research material.

The information on this listing is limited to molecular identity, structural comparison and analytical verification. See the Medical Disclaimer and the Terms and Conditions for sitewide policies.

## Questions and answers

### What kind of molecule is PT-141?

A synthetic cyclic heptapeptide with seven residues, an acetylated N-terminus, a ring closed by a lactam bond and a free carboxylic acid at the C-terminus.

### What closes the ring in PT-141?

An amide bond between the side-chain carboxyl of aspartic acid and the side-chain amine of lysine. There is no cysteine, so no disulfide bond is involved.

### Which formula, mass and CAS number identify PT-141?

The free peptide is C50H68N14O10, with an average mass of about 1025.2 g/mol and a monoisotopic mass of 1024.52428442 Da. Its CAS number is 189691-06-3 and its PubChem CID is 9941379.

### How does PT-141 differ structurally from Melanotan II?

They share the Ac-Nle-cyclo(Asp-His-D-Phe-Arg-Trp-Lys) core. PT-141 ends in a free acid and Melanotan II in an amide, which gives the latter the formula C50H69N15O9 and CAS 121062-08-6.

### Can a mass spectrum tell PT-141 and Melanotan II apart?

Yes, given enough resolution. Their neutral monoisotopic masses differ by about 0.98 Da, and the first isotope peak of Melanotan II lands within roughly 0.02 m/z of PT-141’s main peak, so low-resolution data can blur the two.

### Why is the norleucine residue worth checking?

Norleucine has the same elemental composition as leucine and isoleucine, so an accurate-mass match cannot rule out a substitution. A reference standard or other independent evidence settles it.

### Does the D-phenylalanine change the mass?

No. D-Phe and L-Phe weigh the same, so mass spectrometry alone cannot show the configuration. Chiral analysis or a comparison against a reference standard is used for that.

### Which melanocortin receptors is PT-141 reported to act on in assays?

It is described as a non-selective agonist with activity at MC1R, MC3R and MC4R in cell-based assays. Activity in an assay does not show what a receptor does in a whole organism.

### What do HPLC and mass spectrometry each establish?

HPLC reports chromatographic purity as a peak-area share, and mass spectrometry reports whether the mass fits the expected compound. A clean HPLC trace alone does not show that the peak is PT-141.

### How is PT-141 Spray supplied?

As a 10 mg spray-dispensed bottle with 45 sprays per bottle, labeled for research purposes only.

### How do I match a certificate to my bottle?

Confirm that the lot number on the certificate is the lot you received, then check the compound name, test date, laboratory and method. If you are unsure which lot you hold, ask through the contact page.

### What does Research Use Only mean?

The material is sold for laboratory research and analysis, not for human or veterinary use.

### Does Veracue provide usage instructions for PT-141 Spray?

No. Veracue provides no dosing, administration or usage guidance of any kind, and the material is sold for laboratory research only.

More from Veracue Labs: https://veracuelabs.com/llms.txt