What Is PT-141 Acetate?
PT-141 acetate is the acetate salt of bremelanotide, a synthetic cyclic heptapeptide with the condensed sequence Ac-Nle-c[Asp-His-D-Phe-Arg-Trp-Lys]-OH. It is studied as a melanocortin receptor ligand and is supplied as a bulk research peptide for laboratory and analytical use. PT-141 acetate is not the same as the finished prescription drug Vyleesi, and bulk research material does not inherit FDA approval status.
PT-141 Acetate Identity Table
| Property | Information |
|---|---|
| Name | Bremelanotide acetate |
| Development Code | PT-141 |
| Sequence | Ac-Nle-c[Asp-His-D-Phe-Arg-Trp-Lys]-OH |
| Peptide Length | 7 amino acids (cyclic) |
| CAS (Free Base) | 189691-06-3 |
| CAS (Acetate) | 1607799-13-2 |
| Molecular Formula (Free Base) | C₅₀H₆₈N₁₄O₁₀ |
| Molecular Formula (Acetate) | C₅₂H₇₂N₁₄O₁₂ |
| Molecular Weight (Free Base) | ~1025.2 g/mol |
| Molecular Weight (Acetate) | ~1085.2 g/mol |
| Appearance | White or off-white powder |
| Typical Research Use | Melanocortin receptor research, peptide structure studies and analytical method development |
PT-141 Is a Synthetic Cyclic Heptapeptide
PT-141 is not an ordinary linear short peptide. It is a synthetic cyclic heptapeptide containing seven amino acid residues with several non-standard structural features that are critical to its identity and analytical verification.
The peptide has an N-terminal acetyl group (Ac-) and a C-terminal free carboxylic acid (-OH). The sequence contains norleucine (Nle), a non-proteinogenic amino acid used in place of methionine, as well as D-phenylalanine (D-Phe), whose stereochemical configuration is an important identity attribute.
The defining structural feature is the lactam bridge formed between the side chains of aspartic acid (Asp) and lysine (Lys), creating a constrained cyclic ring. This cyclization is not cosmetic - it constrains the peptide's three-dimensional conformation and is essential to the molecule's identity. A linear peptide with the same amino acid composition is not the same compound.
PT-141 and the Melanocortin Peptide Family
PT-141 belongs to the melanocortin peptide family, a group of molecules related to alpha-melanocyte-stimulating hormone (α-MSH). The endogenous α-MSH is a 13-amino-acid linear peptide with the sequence Ac-SYSMEHFRWGKPV-NH₂. PT-141 is not α-MSH itself; rather, it is a synthetic analog designed around the conserved His-Phe-Arg-Trp pharmacophore found in melanocortin peptides.
The cyclic design of PT-141 serves several research purposes. Cyclization constrains the peptide backbone into a conformation that can interact with melanocortin receptors, while the Nle substitution and D-Phe incorporation improve stability and receptor selectivity relative to the native linear peptide. These modifications mean that PT-141 must be evaluated as a distinct synthetic molecule, not as a simple fragment or derivative of α-MSH.
PT-141 Free Base vs PT-141 Acetate
PT-141 can be supplied in different salt forms, and the distinction between free base and acetate matters for procurement, dosing calculations and analytical documentation.
| Comparison Point | PT-141 Free Base | PT-141 Acetate |
|---|---|---|
| CAS Number | 189691-06-3 | 1607799-13-2 |
| Molecular Formula | C₅₀H₆₈N₁₄O₁₀ | C₅₂H₇₂N₁₄O₁₂ |
| Molecular Weight | ~1025.2 g/mol | ~1085.2 g/mol |
| Mass Basis | Peptide molecule only | Peptide + acetate counter-ion mass |
| Procurement Focus | Identity, purity, content | Identity, purity, content, acetate content |
The acetate form includes acetate as a counter-ion, which contributes to the total powder weight but does not represent additional active peptide. Buyers should confirm the stated assay basis, acetate content and molecular form used for quantitative calculations rather than comparing supplier specifications by HPLC purity or powder weight alone. A product labeled simply "PT-141" without specifying the salt form is insufficient for rigorous procurement.
What Is PT-141 Studied For?
PT-141 is studied primarily as a melanocortin receptor ligand in pharmacological and analytical research contexts. Research areas include receptor pharmacology, ligand-receptor interaction studies, peptide structure-activity relationship investigations, and analytical method development for peptide identification and quantification.
This article does not provide human use recommendations, dosage guidance or therapeutic advice. Bulk PT-141 acetate is intended for laboratory research and analytical use only. Any therapeutic application requires appropriate regulatory authorization and must be conducted under the supervision of qualified medical and regulatory professionals.
Is PT-141 Acetate the Same as an Approved Drug?
No. It is important to distinguish four levels of identity that are often conflated:
Bulk research peptide - PT-141 acetate powder sold for laboratory and analytical use, without finished-product formulation or regulatory approval for therapeutic use.
Active pharmaceutical ingredient (API) - bremelanotide acetate as a drug substance manufactured under pharmaceutical-grade quality and regulatory controls.
Approved finished drug product - a specific formulation, dosage form and delivery device approved by a regulatory authority for a defined indication.
Brand name - Vyleesi, the trade name of the FDA-approved bremelanotide injection product.
Vyleesi was approved by the U.S. FDA in June 2019 as a subcutaneous injection (1.75 mg/0.3 mL) for the treatment of premenopausal women with acquired, generalized hypoactive sexual desire disorder (HSDD). The FDA label explicitly states that Vyleesi is not indicated for HSDD in postmenopausal women or in men, and is not indicated to enhance sexual performance. This approval belongs to the finished drug product only - bulk PT-141 acetate research material does not inherit it.
How Is PT-141 Acetate Identified?
Analytical identification of PT-141 acetate requires multiple orthogonal methods, because no single technique can confirm every aspect of this complex cyclic peptide:
LC-MS (liquid chromatography-mass spectrometry) provides molecular-mass evidence consistent with the claimed bremelanotide peptide. Intact-mass data support peptide identity but do not by themselves establish acetate stoichiometry, amino-acid sequence, cyclization or D-Phe stereochemistry.
HPLC (high-performance liquid chromatography) assesses chromatographic purity by measuring the relative area of the target peak versus peptide-related impurities under a specified method.
Peptide mapping or sequence-related testing provides additional evidence of amino-acid composition and sequence where required.
Acetate content and water content should be evaluated separately where relevant to the supplied form and assay basis, and are measured to establish the actual active-peptide fraction per gram of supplied powder.
Residual TFA and residual solvent testing are performed where applicable to assess purification-related residues.
For a cyclic peptide containing a D-amino acid, identity and stereochemical verification are especially critical. HPLC purity alone cannot confirm that the lactam bridge is properly formed or that the D-Phe configuration is correct. Likewise, intact molecular mass alone cannot distinguish L-Phe from D-Phe because stereoisomers have the same nominal molecular mass. Appropriate orthogonal or stereochemical methods are therefore required when stereochemical confirmation is critical.
Documents Required for B2B Research Purchasing
A credible supplier should provide batch-specific documentation including COA, HPLC chromatogram, LC-MS identity report, peptide assay, acetate content, water content and residual solvent data, all referencing the same batch number. For a detailed guide to evaluating these documents, see How to Evaluate PT-141 Acetate Quality: HPLC, LC-MS and COA Guide.
FAQ
What does PT-141 stand for?
PT-141 is the historical investigational development code name for bremelanotide, a synthetic cyclic heptapeptide studied as a melanocortin receptor ligand.
Is PT-141 a linear or cyclic peptide?
PT-141 is a cyclic heptapeptide. It contains a lactam bridge between the side chains of aspartic acid (Asp) and lysine (Lys), which constrains the peptide conformation. A linear peptide with the same amino acids is not the same compound.
What is the sequence of PT-141?
The condensed sequence is Ac-Nle-c[Asp-His-D-Phe-Arg-Trp-Lys]-OH. It contains seven amino acid residues, including norleucine (Nle) and D-phenylalanine (D-Phe), with an N-terminal acetyl group and a C-terminal free acid.
Why is PT-141 supplied as an acetate?
Acetate is a common counter-ion used in peptide purification and supply. The acetate form includes acetate mass in the total powder weight, so buyers must confirm the stated assay basis, acetate content and molecular form used for quantitative calculations.
How should researchers compare supplier specifications?
Researchers should compare suppliers on an equivalent active-peptide basis: confirm the salt form (free base or acetate), CAS number, molecular-weight reference, peptide assay basis, HPLC purity, acetate content, water content and batch-specific analytical documentation (COA, HPLC chromatogram, LC-MS report).
References
- U.S. Food and Drug Administration. VYLEESI (bremelanotide injection) Prescribing Information. Approval: 2019. https://www.accessdata.fda.gov/drugsatfda_docs/label/2019/210557s000lbl.pdf
- PubChem. Bremelanotide. CID 9941379. National Library of Medicine. https://pubchem.ncbi.nlm.nih.gov/compound/Bremelanotide
- PubChem. Bremelanotide Acetate. National Library of Medicine. https://pubchem.ncbi.nlm.nih.gov/compound/Bremelanotide-Acetate
- DrugBank. Bremelanotide. DB11653. https://go.drugbank.com/drugs/DB11653
Looking for PT-141 acetate powder for laboratory research? HDM Biotech provides batch-specific COA, supporting HPLC chromatogram, LC-MS identity data, peptide assay, acetate and water content analysis, sample support and bulk supply options according to the confirmed product specification.
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