RESEARCH USE ONLY — LABORATORY PROFESSIONALS ONLY:
The NEXALUME LABS research material described in this article, and all sample-preparation information provided here, are intended only for qualified laboratory personnel carrying out controlled in-vitro tests or laboratory animal studies conducted under institutionally approved protocols.
They are not intended for human or veterinary use, administration, consumption, diagnosis, cosmetic use, household preparation, or personal experimentation.
Bremelanotide is also the active moiety of an FDA-approved prescription drug (Vyleesi, approved 2019); this article describes the research-grade material, which is not that approved drug product.
Any information about solvents, concentrations, or sample preparation refers only to laboratory sample handling.
PT-141 is the development code for bremelanotide, a synthetic cyclic heptapeptide melanocortin receptor agonist.
Bremelanotide is also the active moiety of an FDA-approved prescription drug (Vyleesi, approved June 2019).
The research-grade material discussed in this article is not the approved drug product and is not intended for human or veterinary administration.
This article explains its basic chemical identity, receptor activity, COA data, storage, and laboratory sample preparation.
It does not provide instructions for human or veterinary use.
Basic Chemical Information
The free active-moiety bremelanotide peptide has the molecular formula C50H68N14O10, an average molecular weight of about 1,025.2 g/mol, a monoisotopic mass of 1,024.5243 Da, and CAS Registry Number 189691-06-3.[1]
| Item | Information |
|---|---|
| Research name | PT-141 |
| Compound name | Bremelanotide |
| Free active-moiety CAS | 189691-06-3 |
| Acetate-salt CAS | 1607799-13-2; verify the supplied salt form against the batch COA |
| Free active-moiety formula | C50H68N14O10 |
| Average molecular mass (free active moiety) | About 1,025.2 g/mol |
| Monoisotopic mass (free active moiety) | 1,024.5243 Da[1] |
| Number of residues | Seven |
| Sequence | Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH |
| N-terminus | Acetylated |
| C-terminus | Free carboxylic acid |
| Ring structure | Lactam bond between Asp2 and Lys7 |
The peptide ring is formed between the side chains of Asp2 and Lys7.
The N-terminal Nle residue is acetylated, while the C-terminal Lys residue ends as a free acid.[2]
The average molecular mass of 1,025.2 g/mol should not be used as a direct high-resolution mass spectrometry (HRMS) target; the observed LC-MS m/z depends on the charge state, adducts, and whether average or monoisotopic mass is reported.
Free Active Moiety and Acetate Form
Research-grade PT-141 is commonly supplied as an acetate-containing form.
FDA’s description of bremelanotide acetate is C50H68N14O10 · xCH3COOH, with 1 ≤ x ≤ 2.
The molecular weight of 1,025.2 g/mol refers to the free active moiety and does not include acetate, water, or other non-peptide material in the powder.[2]
This difference matters when a laboratory calculates molar concentration.
The calculation should use the free active-moiety-equivalent content or peptide-content value on the batch COA, rather than assuming that all powder in the vial is pure free peptide.
A batch may contain
- the PT-141 peptide,
- acetate or another counterion,
- water,
- small amounts of residual solvent,
- and peptide-related impurities.
The product label, filling record, and batch COA should clearly distinguish net powder fill from assay, peptide content, and free active-moiety-equivalent content. The COA should state the reporting basis (e.g., as-is, anhydrous, or free-active-moiety-equivalent) and the method used to determine peptide content.
Melanocortin Receptor Activity
The melanocortin receptor family contains five subtypes: MC1R, MC2R, MC3R, MC4R, and MC5R. Endogenous ligands of the family include α-, β-, and γ-MSH and ACTH, but ligand preference differs among receptor subtypes; MC2R is selectively activated by ACTH.[3]
PT-141 should not be described as a highly selective MC4R compound. Official receptor data describe it as a nonselective melanocortin receptor agonist with the following general order of potency:
MC1R > MC4R > MC3R > MC5R > MC2R[2]
This order does not mean that the same EC50 value applies to every study.
Results can change when researchers use different receptor species, cell lines, test methods, incubation times, or measuring systems.
For this reason, an article should not give one universal EC50 range unless it also names the original study and explains the exact test conditions.
How PT-141 Is Studied in the Laboratory
Melanocortin receptors commonly signal through the Gs protein and increase cAMP inside a cell. A laboratory can measure this response in cells that have been made to express one receptor type.[3]
Common laboratory tests include
- receptor-binding tests,
- cell-based cAMP tests,
- receptor activation tests,
- receptor internalization tests,
- and comparisons between different melanocortin receptor types.
A response seen after adding PT-141 does not by itself prove that MC4R caused the response.
PT-141 can activate more than one receptor type.
A receptor-specific conclusion normally requires suitable controls, such as cells expressing only one receptor, a receptor blocker, or a matched cell line without the receptor.
How Research Findings Should Be Written
Research statements should clearly say what type of experiment produced the result.
Suitable wording includes “In an in-vitro receptor assay, researchers observed…” or “In a cell-based cAMP test, the study reported…”
Cell-test results and laboratory animal-model results should not be written as proven effects in people.
Animal studies should report, at minimum,
- the species,
- strain,
- sex,
- age,
- sample size and rationale,
- inclusion and exclusion criteria,
- randomization,
- blinding,
- experimental procedures,
- primary endpoint,
- statistical methods,
- and ethics approval.
ARRIVE 2.0 provides full reporting guidance for laboratory animal research.[8]
How to Read a PT-141 COA
A certificate of analysis is a quality-control report for one specific batch. A generic product description or the words “research grade” cannot replace a batch COA.
Mass spectrometry, HPLC purity, peptide content, water, counterion content, and residual solvents are different tests.
They should not be treated as if they measure the same thing.
ICH Q2(R2) lists identity, purity or impurities, and assay or content as separate analytical purposes; these principles are cited as pharmaceutical-quality reference frameworks and do not by themselves establish that a research-use-only batch is manufactured under GMP or is suitable for clinical use.[4]
| COA item | What it tells the laboratory |
|---|---|
| Mass spectrometry | Supports identity by comparing the observed molecular mass or m/z pattern with the expected peptide. Mass matching alone does not confirm the complete sequence, cyclization site, stereochemistry (e.g., D-Phe vs L-Phe), or purity. At least two orthogonal identity methods are recommended (e.g., LC-MS intact mass plus LC-MS/MS sequencing, amino-acid analysis, or peptide mapping). |
| Analytical HPLC | Estimates how much of the detected chromatogram belongs to the main peptide peak under the stated method. Unless relative response factors have been established, area normalization is not necessarily equivalent to molar or mass percentage. It does not by itself measure identity, peptide content, water, counterion, residual solvents, or sterility. |
| Peptide content / assay | Estimates how much free active-moiety-equivalent peptide is present in the powder. The reporting basis (e.g., as-is, anhydrous, or free-active-moiety-equivalent) and the method must be clearly stated. Do not separately subtract acetate, water, or residual solvent from the assayed value if the result is already expressed on an anhydrous, counterion-free basis. |
| Water | Shows how much of the powder mass comes from water (e.g., by Karl Fischer titration). |
| Counterion | Shows the identity and quantitative content of acetate, TFA, or another counterion. For bremelanotide acetate, the acetate content is not a fixed 1:1 stoichiometry; the FDA label describes 1 ≤ x ≤ 2. |
| Residual solvents | Checks for solvents left from synthesis or purification. Testing should be based on solvents actually used or reasonably expected from the process. ICH Q3C(R9) provides a recognized framework for classifying and controlling residual solvents in pharmaceutical products; its principles may be used as reference benchmarks for research peptides, but Q3C is written for drug substances, excipients, and drug products and is not automatically mandatory for every RUO supplier.[6] |
Quality control for synthetic peptides should consider the manufacturing process, peptide-related impurities (including deletion sequences, truncated sequences, epimers, and oxidation products), non-peptide impurities (including residual TFA, elemental impurities, and process reagents), aggregate or oligomer content, specifications, and the methods used to measure them. Additional testing such as endotoxin, bioburden, or sterility may be relevant depending on the intended cell-culture or animal-model application.[5]
COA limitation:
A COA only reports laboratory quality information for a particular raw-material batch.
It does not prove that the material is suitable or safe for human, veterinary, cosmetic, diagnostic, or clinical use.
ICH and EMA guidelines are cited here as pharmaceutical-quality reference frameworks; they do not by themselves establish that a research-use-only batch is manufactured under GMP or is suitable for clinical use.
Storage of Lyophilized PT-141
For long-term storage of dry lyophilized material, −20°C to −80°C is a common conservative laboratory range.
Lot-specific instructions and demonstrated stability data take precedence over general storage guidance.
General peptide-handling literature recommends low-temperature storage, limited exposure to air and moisture, and protection from light for sensitive peptide sequences.[7]
Before opening a cold vial, allow the sealed vial to reach room temperature. This helps reduce condensation and moisture entering the vial.
PT-141 contains a tryptophan residue.
Oxidation and photochemical degradation should be considered during method development and stability assessment.
Unnecessary exposure to air and strong light should be minimized unless lot-specific stability data demonstrate otherwise.[7]
Laboratory Sample Preparation
LABORATORY SAMPLE PREPARATION ONLY:
This section is limited to analytical and cell-based laboratory work.
It is not a dosing, injection, administration, or household preparation guide.
PT-141 does not have one universal solvent or one universal solubility value that applies to every batch and every concentration.
Solubility can change with the salt form, concentration, pH, temperature, and solvent.
The solvent should be selected from the lot-specific product information, the target concentration, the needs of the planned assay, the acceptable pH range, and the solvent tolerance of the cells, enzymes, or detection method.
After preparation, record the lot number, solvent, concentration basis, preparation date, storage temperature, and freeze–thaw history.
Prepared solutions should be divided into small laboratory aliquots when suitable for the assay.
Repeated freezing and thawing should be avoided.
A fixed solution-storage period should not be claimed unless it is supported by batch information or a stability test.[7]
Concentration Calculations
Laboratory concentration calculations must use the correct peptide amount.
The free active-moiety-equivalent molar concentration may be calculated as:
C (mol/L) = mpowder (g) × fBMT,base ÷ 1,025.2 (g/mol) ÷ V (L)
where mpowder is the weighed powder mass, fBMT,base is the bremelanotide free active-moiety-equivalent mass fraction as stated on the COA, and V is the final total volume.
Do not separately subtract acetate, water, or residual solvent from the assayed value if the COA result is already expressed on an anhydrous, counterion-free basis.
The COA reporting basis must be confirmed before applying this formula.
Gross powder weight should not automatically be used as pure free-active-moiety weight because the powder may also contain acetate, water, residual solvent, and other non-peptide material. Different suppliers may define “peptide content,” “assay,” and “net peptide content” differently; verify the definition and calculation basis before use.
This formula is included only to explain laboratory concentration records.
It must not be used as a human or veterinary dosing calculation.
Research References
- National Center for Biotechnology Information. PubChem Compound Summary for Bremelanotide, CID 9941379.
View source - U.S. Food and Drug Administration. VYLEESI (bremelanotide injection) prescribing information, Sections 11 and 12.1. Initial U.S. Approval: 2019.
View source - IUPHAR/BPS Guide to Pharmacology. Melanocortin Receptors.
View source - International Council for Harmonisation. ICH Q2(R2): Validation of Analytical Procedures, corrected 2025 version.
View source - European Medicines Agency. Guideline on the Development and Manufacture of Synthetic Peptides (EMA/CHMP/CVMP/QWP/367182/2025, effective 1 June 2026).
View source - International Council for Harmonisation. ICH Q3C(R9): Impurities — Guideline for Residual Solvents.
View source - Hoofnagle AN, Whiteaker JR, Carr SA, et al. Recommendations for the generation, quantification, storage, and handling of peptides used for mass-spectrometry-based assays. Clinical Chemistry. 2016;62(1):48-69. doi:10.1373/clinchem.2015.250563.
View source - ARRIVE Guidelines. ARRIVE 2.0 reporting guidance for laboratory animal research.
View source
Research Use Only Disclaimer
Research Use Only: The bremelanotide/PT-141 research material supplied by NEXALUME LABS is intended and labeled solely for laboratory research use.
It is not the approved Vyleesi (bremelanotide injection) drug product and is not intended, manufactured, tested, or released for human or veterinary administration.
This article provides general scientific information regarding standard laboratory in vitro and in vivo research contexts only, and does not constitute a validated experimental protocol, medical guidance, clinical guidance, veterinary guidance, or treatment advice.
