PT-141 Molecular Weight, Sequence & CAS Reference

Chemical Profile and Core Molecular Specifications of PT-141

PT-141, chemically designated as Bremelanotide, is a synthetic cyclic heptapeptide derived from the broader class of melanocortin receptor agonists. Originally synthesized during investigations into skin pigmentation via α-MSH analogs, PT-141 was isolated after researchers noted distinct central nervous system receptor activation patterns separate from peripheral melanogenesis. In laboratory settings, PT-141 is primarily studied for its role as a selective agonist at melanocortin receptors, specifically the MC3R and MC4R subtypes, which modulate central physiological responses involved in neuroendocrine signaling and sexual-health pathways.

To establish precise concentration values during quantitative assays, laboratory investigators must rely on exact physicochemical specifications. PT-141 possesses a empirical molecular formula of C50H68N14O10 and a calculated monoisotopic mass of 1024.52 Da, with a standard average molecular weight of 1025.18 g/mol. The compound is officially indexed in the Chemical Abstracts Service registry under CAS Number 189691-06-3. For experimental bench work requiring verified molecular standards, researchers can reference the complete spectrum of cataloged items in our all peptides hub.

Understanding these baseline chemical metrics is vital when conducting liquid chromatography-mass spectrometry (LC-MS) or nuclear magnetic resonance (NMR) spectroscopy. Small variations in molecular mass calculations can significantly alter molarity calculations during *in vitro* binding assays or electrophysiological experiments. Researchers utilizing high-purity research materials must verify that physical lot attributes match published parameters prior to experimental initiation.

Primary Amino Acid Sequence and Cyclic Structure Analysis

The primary sequence of PT-141 is defined as Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH. Structurally, PT-141 is a synthetic derivative of Melanotan II (MT-2), retaining the core pharmacophore sequence required for melanocortin receptor activation while featuring a modified C-terminus. The sequence incorporates non-proteinogenic amino acids, specifically Nle (Norleucine) at position 1 and a D-enantiomer configuration of Phenylalanine (D-Phe) at position 4 within the ring, which imparts enhanced enzymatic resistance against central endopeptidases.

The defining structural hallmark of PT-141 is its side-chain-to-side-chain lactam cyclization. The cyclic core is formed through an amide bond bridge spanning the carboxyl side chain of Aspartic Acid (Asp) at position 2 and the epsilon-amino side chain of Lysine (Lys) at position 7. This intramolecular cyclization constrains the peptide into a stable beta-turn conformation, preserving the receptor-binding domain (His-D-Phe-Arg-Trp) in a rigid spatial arrangement optimized for melanocortin receptor interaction.

This structural rigidity drastically reduces conformational entropy compared to linear endogenous peptide ligands like native α-MSH. As a result, PT-141 exhibits enhanced receptor affinity and prolonged biological half-life in preclinical test systems. Investigating researchers examining sequence dynamics can review lot-specific analytical data directly via our third-party COA registry.

Salt Forms, Counterion Dynamics, and Net Peptide Content

In commercial and research synthesis, PT-141 is typically isolated as a lyophilized powder in a salt form—most commonly as an acetate salt (Bremelanotide Acetate) or, less frequently, a trifluoroacetate (TFA) salt. During solid-phase peptide synthesis (SPPS), acidic cleavage and purification buffers introduce counterions that associate with basic amino acid residues (such as the Arg and Lys side chains and the N-terminal amine). Understanding the presence of these counterions is critical for accurate gravimetric preparation.

The gross mass weighed on a laboratory balance includes the active peptide cation, residual bound counterions (e.g., acetate or TFA anions), and bound moisture (hydrophobic and hydrophilic water of hydration). The Net Peptide Content (NPC) represents the actual percentage of dry weight composed strictly of the target peptide chain. Typically, high-grade lyophilized PT-141 exhibits a net peptide content ranging between 80% and 90%, with the remainder comprised of counterions and residual moisture.

To calculate exact molar concentrations for *in vitro* tissue bath or receptor binding assays, researchers must adjust the weighed mass using the lot-specific Net Peptide Factor derived from nitrogen analysis or amino acid analysis (AAA). Failing to account for salt content will introduce systematic errors, underestimating the actual peptide concentration required for quantitative biochemical evaluation. For accurate bench calculations, scientists are encouraged to utilize our interactive reconstitution calculator.

Receptor Target Dynamics and Preclinical Research Applications

In preclinical model systems, PT-141 operates primarily as a potent agonist of central melanocortin receptors. Unlike early melanocortin peptides that preferentially target peripheral MC1R to drive melanogenesis, PT-141 exhibits significant binding affinity for MC3R (Ki ≈ 5.3 nM) and MC4R (Ki ≈ 0.83 nM). Experimental data indicate that the activation of central MC4R pathways in hypothalamic regions, including the paraventricular nucleus (PVN), plays a key role in modulating autonomic neuroendocrine responses.

Preclinical investigations utilizing rodent models have established that PT-141 crosses the blood-brain barrier following systemic administration to engage central melanocortin pathways. Studies investigating central nervous system circuits demonstrate that PT-141-induced MC4R activation leads to downstream modulation of dopamine release within the mesolimbic pathway. This central mechanism distinguishes PT-141 from vasoactive agents, making it an invaluable pharmacological tool for researching central signaling networks linked to behavioral and sexual-health pathways.

Furthermore, researchers explore PT-141 in cellular assays to evaluate intracellular cyclic adenosine monophosphate (cAMP) accumulation. Upon agonist binding to the G-protein coupled melanocortin receptor, adenylyl cyclase is activated, converting ATP to cAMP. Quantifying cAMP accumulation across various cell lines expressing wild-type or mutant MC4R receptors provides critical insights into signal transduction dynamics, receptor desensitization, and arrestin recruitment.

Comparative Structural Analysis: Melanocortin Receptor Agonists

To contextualize PT-141 within the broader landscape of melanocortin research compounds, it is useful to compare its structural attributes against closely related peptides in the class. Structural modifications directly dictate receptor subtype selectivity, metabolic stability, and signaling bias. Below is a comparative overview of key parameters across prominent research melanocortins:

When evaluated alongside related compounds, PT-141 stands out due to its removal of the C-terminal amide group present in Melanotan II, replacing it with a free carboxylic acid C-terminus (Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH). This subtle functional group alteration shifts the receptor selectivity profile, reducing MC1R binding affinity relative to MC4R, thereby minimizing peripheral melanogenic responses during neurobiological investigations. Researchers can explore additional structural profiles across our research library hub.

Analytical Verification Protocols: Mass Spectrometry and Chromatographic Purity

Ensuring experimental reproducibility requires rigorous analytical validation of PT-141 identity and purity. At PX1 Research, every lot undergoes stringent quality control testing using orthogonal analytical methods, including High-Performance Liquid Chromatography (HPLC) coupled with Electrospray Ionization Mass Spectrometry (ESI-MS). HPLC testing utilizes reverse-phase C18 columns with gradient elution (water/acetonitrile containing 0.1% TFA) to isolate and quantify organic impurities.

Mass spectrometry confirms the exact monoisotopic mass and charge states of the cyclic peptide. Under positive ion ESI-MS mode, PT-141 typically displays prominent protonated molecular ions at [M+H]+ m/z 1025.5 and doubly charged species at [M+2H]2+ m/z 513.3. Comparing observed fragmentation patterns against theoretical mass spectra confirms intact lactam bridge integrity and rules out sequence truncation or linear precursor contamination.

In addition to purity and identity confirmation, analytical testing for research-grade peptides must include quantification of bacterial endotoxins via Limulus Amebocyte Lysate (LAL) assays. PX1 Research enforces strict limits, ensuring endotoxin levels remain below 0.05 EU/mg. This guarantees that cell culture systems and animal tissue models remain free from confounding pyrogenic interference during sensitivity assays. Standardized samples of PT-141 10mg are shipped with full analytical documentation for verification.

Solubility, Reconstitution, and Storage Stability Protocols

Lyophilized PT-141 acetate exhibits excellent solubility in aqueous solutions due to its polar residues and cyclic conformation. For laboratory reconstitution, standard laboratory protocols utilize sterile Bacteriostatic Water (0.9% benzyl alcohol) or sterile phosphate-buffered saline (PBS, pH 7.4). When reconstituting, the solvent should be introduced along the internal glass wall of the vial, followed by gentle swirling. Direct high-shear agitation or vigorous shaking must be avoided to prevent mechanical shearing or surface-induced peptide aggregation.

Long-term stability of the lyophilized powder is optimized when stored at -20°C to -80°C in a desiccated environment protected from light exposure. Under these conditions, the intact cyclic structure remains stable for up to 24 months without significant hydrolytic degradation or oxidation of the Tryptophan (Trp) residue. Once reconstituted, stock solutions should be aliquoted into single-use polypropylene microcentrifuge tubes to prevent repeated freeze-thaw cycles.

Reconstituted liquid stock solutions stored at 4°C maintain analytical stability for up to 30 days. For longer storage of aqueous aliquots, keeping samples at -80°C is recommended, though researchers must account for potential cryo-concentration effects. Detailed handling guidelines and bulk procurement options for institutional laboratories are available through our wholesale lab account portal.

Quality Assurance Standards at PX1 Research

PX1 Research is committed to supplying high-purity research compounds synthesized in state-of-the-art USA-based facilities adhering to GMP-compliant quality management standards. Every lot of PT-141 is subjected to rigorous independent testing in ISO 17025 accredited analytical laboratories. This comprehensive verification process includes HPLC purity assessment, mass spectrometry structural confirmation, moisture content analysis, counterion determination, and endotoxin screening.

We prioritize supply chain transparency and analytical integrity, ensuring that every vial delivered to your facility strictly adheres to the stated specifications. Orders placed Monday through Friday ship same-day from our distribution centers in California and Arizona. Researchers can rely on PX1 Research for consistent, highly pure materials designed to produce verifiable and reproducible data across preclinical research applications.