cyclic heptapeptide raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
Reviewed 2026-08-01. Anything still debated is marked as such rather than presented as settled.
Melanotan-2, also written Melanotan II, is a synthetic cyclic heptapeptide designed as an analogue of alpha-melanocyte-stimulating hormone. Its sequence is Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2, and the lactam bridge between the aspartate and lysine side chains constrains the peptide into a ring. This structural change increases receptor affinity and metabolic stability relative to the native hormone. The compound was created in the 1980s as a research tool for studying pigmentation biology.
Melanocytes are the pigment-producing cells of the skin, and they carry melanocortin-1 receptors on their surface. When the receptor is activated, cyclic adenosine monophosphate rises inside the cell and raises the activity of enzymes such as tyrosinase, which increases melanin output. Melanotan-2 binds melanocortin-1 receptors in vitro and in animal models, and this binding is generally described as the basis for the tanning effect. Other receptors account for different effects: melanocortin-4 receptors contribute to appetite and erectile signalling, while melanocortin-3 and melanocortin-5 receptors contribute to energy balance and exocrine function.
The compound was developed in the late 1980s and 1990s by academic researchers investigating photoprotection. The rationale held that stimulating melanin production might reduce ultraviolet damage to skin and lower skin cancer risk. Early work examined receptor binding, pigment response, and short-term tolerability in small studies. That program did not produce an approved drug, and formal development stalled after early-phase trials. Whether induced pigmentation confers meaningful photoprotection remains an open question.
Outside regulated medicine, melanotan II circulates through online vendors as a research chemical, often marketed for tanning. Products sold this way vary widely in purity, concentration, and labeling accuracy, and independent testing has documented discrepancies. Published reports describe both pigment effects and adverse reactions, including nausea, flushing, and darkening of existing moles. Long-term safety data are sparse, and no large controlled trial has established a risk profile. Questions about cumulative effects on melanocytes remain unresolved in the literature.
Melanotan II is a synthetic peptide analog modeled on alpha-melanocyte-stimulating hormone, a naturally occurring signaling peptide involved in pigmentation. Its structure is a cyclic heptapeptide containing two non-natural substitutions, norleucine at position four and D-phenylalanine at position seven. These modifications resist enzymatic breakdown and extend the molecule's activity relative to the native hormone. The compound binds melanocortin receptors and is studied mainly as a pharmacological tool rather than a therapeutic product. It has never received approval as a medicine in any major jurisdiction.
| Property | Value | Notes |
|---|---|---|
| Compound class | Synthetic cyclic heptapeptide | Alpha-MSH analogue containing a D-phenylalanine residue |
| Molecular formula | C50H69N15O9 | Average molecular mass approximately 1024.2 g/mol |
| Appearance | White to off-white lyophilised powder | Normally supplied as a freeze-dried solid in a sealed vial |
| Solubility | Freely soluble in water and polar solvents | Dissolves readily in aqueous buffers and in alcohol-water mixtures |
| Receptor targets | MC1R, MC3R, MC4R, MC5R | Acts as a non-selective melanocortin receptor agonist |
Published pharmacokinetic information is limited and comes mainly from small studies rather than registrational trials. Plasma half-life is usually described as short, on the order of tens of minutes, followed by rapid tissue distribution and clearance of the intact peptide. Metabolites and low concentrations of parent compound have been reported in urine, a detail relevant to anti-doping and forensic testing. Whether repeated exposure changes receptor sensitivity or clearance over time remains an open question. Values differ noticeably between analytical assays, so published numbers should be read as approximate rather than definitive.
Melanotan II is a synthetic cyclic heptapeptide with the sequence Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2, corresponding to a molecular formula of C50H69N15O9 and a monoisotopic mass near 1024 daltons. It was designed as a structural analogue of alpha-melanocyte-stimulating hormone, a peptide hormone produced by cleavage of proopiomelanocortin. A lactam bridge between the aspartate and lysine side chains closes the ring, and the C-terminal amide removes a free carboxyl group. Both modifications increase resistance to enzymatic degradation compared with the linear parent hormone. Four substitutions distinguish it from afamelanotide, the linear analogue studied under the name melanotan I.
Receptor-binding studies classify melanotan II as a non-selective melanocortin agonist. It interacts with MC1R, MC3R, MC4R and MC5R, with reported affinities in the low nanomolar range and no strong subtype preference. Activation of MC1R on dermal melanocytes shifts pigment synthesis toward eumelanin, the dark polymer deposited in melanosomes and transferred to keratinocytes. Because the same peptide engages MC4R in the hypothalamus, it also appears in animal work on food intake and erectile response, which is why it is discussed in both pigment and metabolic research. Which receptor populations dominate after systemic exposure in humans is not fully established.
== History == Nitrogen mustards arose from the derivatization of sulphur mustard gas after military personnel exposed to it during World War I were observed to have decreased white blood cell counts. Since the sulphur mustard gas was too toxic to be used in humans, Gilman hypothesized that by reducing the electrophilicity of the agent, which made it highly chemically reactive towards electron-rich groups, then less toxic drugs could be obtained. To this end, he made analogues that were less electrophilic by exchanging the sulphur with a nitrogen, leading to the nitrogen mustards. With an acceptable therapeutic index in humans, nitrogen mustards were first introduced in the clinic in 1946. Aliphatic mustards were developed first, such as mechlorethamine hydrochloride (mustine hydrochloride), which is still used in the clinic today. In the 1950s, aromatic mustards like chlorambucil were introduced as less toxic alkylating agents than the aliphatic nitrogen mustards, proving to be less electrophilic and react with DNA more slowly. Additionally, these agent can be administered orally, a significant advantage. Chlorambucil was first synthesized by Everett et al.
==== Price regulations ==== In a bid to lower soaring gas prices, Castillo reintroduced liquefied petroleum gas (LPG) to the Fuel Price Stabilization Fund (FEPC). The FEPC was created in 2002 and serves as a price support by giving a range of minimum and maximum consumer prices. In theory, the FEPC is self-sustaining. Should the price of gas be above the maximum consumer price, the FEPC will subsidize the cost for consumers. If the price of gas is below the minimum consumer price, then the profits will be given to the FEPC. However, LPG was removed from the FEPC in 2020, due to financial costs and scepticism on whether consumer prices were affected by the fiscal intervention. The reintroduction of LPG to the FEPC by Castillo reversed the 2020 policy decision. Additionally, while Pedro Castillo's Economic Minister Pedro Francke and then Prime Minister Guido Bellido have denied any plans to institute price controls, the Free Peru caucus later attempted to modify the constitution to implement them. The amendment would have allowed the state to regulate the "supply and prices of goods and services produced by public and private companies" due to shortages or a state of emergency. However, the amendment failed to pass within the opposition-controlled Congress.
=== COSMIC: Identification confidence === The COSMIC confidence score assigns a confidence to CSI:FingerID structure identifications. The idea is similar to False Discovery Rates: All molecules in a large dataset are analysed using CSI:FingerID, the top-ranked hit for each molecule will be evaluated by COSMIC and the most trustworthy identifications can be selected for further analysis. COSMIC does not re-rank structure candidates of a particular molecule nor does it discard any identifications. COSMIC employs a confidence score that combines E-value estimation and a linear support vector machine (SVM) with enforced directionality. Calibration of CSI:FingerID scores is achieved using E-value estimates. Generating decoys for small molecule structures is a non-trivial task, that is why candidates in PubChem serve as a proxy for decoys here. The score distribution is modeled as a mixture distribution of log-normal distributions, and the P-value and E-value of a hit score are estimated using the kernel density estimate of PubChem candidate scores. The SVM is employed to classify whether a hit is correct, utilizing features such as the calibrated score, score differences to other candidates, the total peak intensity explained by the fragmentation tree, and the cardinality of molecular fingerprints. Learning is constrained to a linear SVM to mitigate the risk of overfitting, and the directionality of features is enforced. This involves making upfront decisions about whether high or low values of a feature should enhance the confidence in an identification.
==== Iraq ==== Over 50 think tanks have emerged in Iraq, particularly in the Kurdistan Region. Iraq's leading think tank is the Middle East Research Institute (MERI), based in Erbil. MERI is an independent non-governmental policy research organization, established in 2014 and publishes in English, Kurdish, and Arabic. It was listed in the global ranking by the United States's Lauder Institute of the University of Pennsylvania as 46th in the Middle East.
Sources: en.wikipedia.org
Marcus S. Albernaz, MD Shirley A. Carraway, Ed.D. James W. "Jim" Chestnutt Charlester T. Crumpler, Jr. Ernest L. "Ernie" Evans Jimmy F. Garris Robert J. "Bob" Greczyn, Jr. W. Phillip "Phil" Hodges J. Bryant Kittrell, III C. Bynum Satterwhite Anand "Andy" Tewari, MD
The two substrates of this enzyme are D-sorbitol 6-phosphate and oxidised nicotinamide adenine dinucleotide (NAD+). Its products are fructose 6-phosphate (shown in its open-chain form), reduced NADH, and a proton. This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-OH group of donor with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is D-sorbitol-6-phosphate:NAD+ 2-oxidoreductase. Other names in common use include ketosephosphate reductase, ketosephosphate reductase, D-sorbitol 6-phosphate dehydrogenase, D-sorbitol-6-phosphate dehydrogenase, sorbitol-6-P-dehydrogenase, and D-glucitol-6-phosphate dehydrogenase. This enzyme participates in fructose and mannose metabolism.
The Streptavidin-Binding Peptide (SBP)-Tag is a 38-amino acid sequence that may be engineered into recombinant proteins. Recombinant proteins containing the SBP-Tag bind to streptavidin and this property may be utilized in specific purification, detection or immobilization strategies. The sequence of the SBP tag is MDEKTTGWRGGHVVEGLAGELEQLRARLEHHPQGQREP.
==== Empirical correlations ==== Empirical correlations are simple mathematical expressions intended to approximate a liquid's properties over a range of experimental conditions, such as varying temperature and pressure. They are constructed by fitting simple functional forms to experimental data. For example, the temperature-dependence of liquid viscosity is sometimes approximated by the function
=== Joint operation against Niño Guerrero === In June 2026, a military operation was carried to kill Héctor Rusthenford Guerrero Flores, known as Niño Guerrero, the leader of the Venezuelan criminal gang Tren de Aragua. US president Donald Trump announced that Guerrero was killed in a airstrike on 12 June in Venezuela conducted in coordination with Venezuelan authorities. Venezuelan officials confirmed their participation in the operation.
Sources: en.wikipedia.org
No. It is a laboratory-made peptide, while the natural hormone is alpha-melanocyte-stimulating hormone, a longer peptide produced by the pituitary gland and by skin cells. Melanotan-2 mimics only a short active region of that hormone and contains non-natural residues such as D-phenylalanine.
No approved regulatory indication exists in major markets. An approval exists for a different peptide, afamelanotide, which is used for a rare photosensitivity disorder called erythropoietic protoporphyria. Melanotan-2 itself remains a research compound with no cleared clinical role.
Melanocortin-1 receptors on melanocytes are the receptor most closely linked to pigment production. The peptide is not selective, however, and also activates melanocortin-3, melanocortin-4, and melanocortin-5 receptors. That lack of selectivity is the usual explanation offered for both its range of observed effects and its off-target effects.
It is a synthetic cyclic peptide designed as an analog of alpha-melanocyte-stimulating hormone. It acts on melanocortin receptors and is best known from research into pigmentation. It is not an approved pharmaceutical product.