cyclic heptapeptide is one of those subjects where the details matter more than the headlines. This page pulls together the background, the mechanisms, and the practical points readers ask about most.
Last reviewed on 2026-07-31. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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.
Melanotan-2 is a synthetic cyclic heptapeptide designed as an analogue of alpha-melanocyte-stimulating hormone. Its sequence incorporates a lactam bridge that constrains the peptide into a ring, which increases resistance to enzymatic breakdown relative to the natural hormone. Researchers at the University of Arizona synthesised the compound in the late 1980s and early 1990s while studying pigmentation pathways. It has never received marketing approval from any national medicines regulator. In the scientific literature it is usually described as a laboratory research reagent rather than a therapeutic product.
The peptide acts as a non-selective agonist at melanocortin receptors, showing affinity for MC1R, MC3R, MC4R and MC5R. Activation of MC1R on melanocytes drives the conversion of tyrosine into melanin and shifts production toward the darker eumelanin form. MC4R signalling in the central nervous system is linked to appetite and energy balance, which helps explain why reduced food intake appeared in early human studies. Effects on MC4R and on vascular tone also account for the erectile responses recorded as unexpected findings in those same trials.
Melanotan-2 is frequently confused with afamelanotide, a linear analogue authorised in the European Union for erythropoietic protoporphyria. The two compounds differ in chain length, ring structure and receptor selectivity, so findings for one cannot be transferred directly to the other. Published controlled human data on melanotan-2 remain sparse, and much of what circulates online derives from small studies or unpublished reports. Questions about effect size, dose-response behaviour and long-term safety therefore remain unresolved.
| Property | Value | Notes |
|---|---|---|
| Chemical class | Synthetic cyclic heptapeptide | Belongs to the melanocortin agonist family |
| Key substitutions | Nle4 and D-Phe7 | Improve resistance to enzymatic degradation |
| Molecular formula | C50H69N15O9 | Approximately 1024 g/mol |
| Regulatory status | Not approved as a medicine | Distributed as a research chemical |
| Common synonyms | Melanotan II, MT-II, MT-2 | Spelling varies across sources |
Melanotan-2 is a synthetic cyclic heptapeptide designed as an analogue of alpha-melanocyte-stimulating hormone, the naturally occurring peptide involved in pigmentation signalling. Its sequence is conventionally written as Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2, with a lactam bridge joining the aspartate side chain to the lysine side chain. The empirical formula is C50H69N15O9 and the monoisotopic mass lies near 1023.5 daltons. N-terminal acetylation and the D-configured phenylalanine both increase resistance to enzymatic breakdown compared with the parent hormone.
Pharmacologically, melanotan-2 behaves as a non-selective agonist across the melanocortin receptor family. Binding at MC1R on dermal melanocytes promotes eumelanin synthesis, which underlies the tanning response described in early human work. Activity at the centrally expressed MC4R receptor is associated with reported effects on appetite and erectile function. Because the peptide does not discriminate strongly among receptor subtypes, attributing any single observed effect to one receptor pathway is generally not possible without selective antagonists or receptor knockout models.
Melanotan II is a synthetic cyclic heptapeptide that acts as an agonist at melanocortin receptors. It was designed as a structural analogue of alpha-melanocyte-stimulating hormone, the endogenous peptide involved in pigment production. The analogue carries a lactam bridge that constrains the ring and slows enzymatic breakdown relative to the native hormone. In research literature it appears under several abbreviations, and naming conventions are not fully standardized. Published descriptions usually place it within the broader melanocortin agonist family.
Receptor binding at MC1R on melanocytes raises intracellular cyclic AMP and increases expression of tyrosinase and related enzymes. The downstream result is greater synthesis of eumelanin, the dark pigment, without ultraviolet exposure acting as the trigger. The compound is not selective, however, and also engages MC3R, MC4R and MC5R, which are expressed in the central nervous system and elsewhere. That lack of selectivity is the explanation usually offered for effects reported outside pigmentation, including appetite suppression and nausea. Selectivity remains a central theme in comparative studies of related peptides.
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.
Early published reports described melanotan-2 as a tanning agent without sun protection, which means darkening is not the same as protection against ultraviolet radiation. Later studies explored the peptide in erectile dysfunction, hemorrhagic shock, and some skin conditions. No regulator in the United States or Europe has approved it for clinical use. Many products labelled melanotan-2 are sold without approval and their identity and purity are unverified. Its long-term safety in humans remains an open question.
Published human data come mostly from small, short studies rather than large controlled trials. Reported outcomes include increased skin pigmentation and, in some reports, effects on appetite and libido, but sample sizes are small and follow-up is limited. Whether long-term use produces durable pigment changes or adverse effects is not established. Because products sold outside pharmacies are not standardized, the actual content of any given vial is often unknown. Independent testing of such material is uncommon.
Melanotan II is a synthetic cyclic heptapeptide analog derived from the core sequence of alpha-melanocyte-stimulating hormone. Researchers at the University of Arizona synthesized it during the 1980s while studying pigmentation and appetite signaling. The compound is not an approved medicine in any major jurisdiction and appears mainly in laboratory and research-chemical settings. Its structure incorporates a lactam bridge between side chains, which constrains the ring and slows enzymatic breakdown relative to the natural hormone.
Melanotan II binds several melanocortin receptor subtypes rather than a single target. MC1R on melanocytes drives melanin synthesis, while MC3R and MC4R participate in energy balance, appetite, and sexual response pathways. This lack of selectivity explains why reported effects extend beyond skin darkening. Substitutions at positions four and seven, including norleucine and D-phenylalanine, increase potency and resistance to peptidases. Understanding which receptor mediates which effect remains an active area of investigation.
=== Acting and filmmaking === Samberg majored in experimental film. He became an online star and made his own comedy videos with his friends Akiva Schaffer and Jorma Taccone. When YouTube was created in 2005, the streaming of their videos became much more widespread. Samberg became a featured player on Saturday Night Live in part because of the work he had done on his sketch comedy website TheLonelyIsland.com, which helped him land an agent and eventually get hired at Saturday Night Live. Prior to joining its cast, Samberg was (and remains) a member of the comedy troupe the Lonely Island, along with Taccone and Schaffer. The trio began writing for Saturday Night Live in 2005 and released their debut album Incredibad in 2009. Samberg appeared in numerous theatrical films, commercials, music videos, and hosted special events, including the 2009 MTV Movie Awards. In 2012, Samberg delivered the Class Day speech at Harvard University, and he starred with Adam Sandler in That's My Boy. The same year, he starred with Adam Sandler again in Hotel Transylvania as Jonathan, a role he reprised for its sequels Hotel Transylvania 2, Hotel Transylvania 3: Summer Vacation and Hotel Transylvania: Transformania. In September 2012, Samberg played Cuckoo in the BAFTA nominated BBC Three series Cuckoo; and, in 2013, he landed the role of Detective Jake Peralta in Fox's (later NBC's) police sitcom Brooklyn Nine-Nine, which first aired on September 17 of the same year. Samberg won the Golden Globe Award for Best Actor – Television Series Musical or Comedy in 2014 for his role as Peralta.
===== Bangladesh ===== American ties with Bangladesh were strained during Sheikh Hasina's rule, due to American accusations of human rights violations; India discouraged the United States from pressing too hard on these accusations to avoid giving ground to Islamist parties in future Bangladeshi elections. However, under Bangladesh's Yunus ministry, Bangladesh-US relations have improved, though Bangladesh's ties with India have worsened.
=== Leg surgery === In surgeries, the principle superficial neurovascular bundles at risk are, medially, the great saphenous vein and its accompanying nerve, and, laterally, the superficial peroneal nerve. The superficial peroneal nerve originates from the common peroneal nerve near the neck of the fibula and passes between the peroneus longus and brevis muscles, supplying motor branches to these muscles. The superficial branch then continues onto the dorsum of the foot to supply sensory fibers to the skin there. The main deep neurovascular bundle at risk is the posterior tibial artery. It lies on the posterior aspect of the tibialis posterior and flexor digitorum longus muscle, and medial to the belly of flexor hallucis longus muscle. It also gives rise to medial plantar artery and lateral plantar artery. During surgery, these neurovascular bundles, both superficial and deep, should be protected in order to prevent neurological damage. A common anatomically informed, surgical technique to avoid damaging neurovascular bundles is to undermine anteriorly to the posterior tibial margin after reaching the fascia, in order to avoid the saphenous vein and nerve. The deep posterior compartment here is superficial and readily accessible. The fascia of the deep posterior compartment is carefully opened distally and proximally, under the belly of the soleus muscle, paying special attention to the posterior tibial neurovascular bundle.
Sources: en.wikipedia.org
They can be synthesized/released and broken down again in specific reactions by enzymes or ion channels. Some (such as Ca2+) can be stored in special organelles and quickly released when needed. Their production/release and destruction can be localized, enabling the cell to limit space and time of signal activity.
=== Non-ribosomal peptide synthase === The non-ribosomal peptide synthase (NRPS) is encoded by three genes: CepA, CepB, and CepC. CepA links the first three amino acids; CepB adds the fourth to sixth amino acids; CepC adds the last amino acid and includes a thioesterase domain to release the heptapeptide from the NRPS complex. The growing peptide chain is passed through modules for each amino acid. The basic organization of each module is A-PCP-C. The A, or adenylation, region activates the domain's amino acid to allow transfer to the PCP, or peptide carrying protein, region. The activated amino acid is transferred to a cysteine residue in the PCP region, which anchors the amino acid and prepares the amino acid to be added to the polypeptide. The C, or condensation, region attaches the amino acid to the polypeptide. In addition, modules 2, 4, and 5 have E regions that epimerize (switch the stereochemistry) of the added amino acid to produce the correct configuration. Module 7, the last module, has an X and TE region. The X region is responsible for recruiting several of the tailoring enzymes that will perform the necessary reactions (halogenation, glycosylation, methylation, oxidative cross-linking, and hydroxylations) to produce chloroeremomycin. Finally, the TE, or thioesterase, region releases chloroeremomycin from the NRPS complex.
Money serves three purposes: a store of value, a medium of exchange, and a unit of account. According to The Economist in 2014, bitcoin functions best as a medium of exchange. In 2015, The Economist noted that bitcoins had three qualities useful in a currency: they are "hard to earn, limited in supply and easy to verify". However, a 2018 assessment by The Economist stated that cryptocurrencies met none of these three criteria. Per some researchers, as of 2015, bitcoin functions more as a payment system than as a currency. In 2014, economist Robert J. Shiller wrote that bitcoin has potential as a unit of account for measuring the relative value of goods, as with Chile's Unidad de Fomento, but that "Bitcoin in its present form... doesn't really solve any sensible economic problem". In 2017, François Velde, senior economist at the Chicago Fed, described bitcoin as "unlikely by itself to replace monies in well-functioning monetary systems." The legal status of bitcoin varies substantially from one jurisdiction to another. Because of its decentralized nature and its global presence, regulating bitcoin is difficult. However, the use of bitcoin can be criminalized, and shutting down exchanges and the peer-to-peer economy in a given country would constitute a de facto ban. The use of bitcoin by criminals has attracted the attention of financial regulators, legislative bodies, and law enforcement. Nobel-prize winning economist Joseph Stiglitz says that bitcoin's anonymity encourages money laundering and other crimes. This is the main justification behind bitcoin bans.
Sources: en.wikipedia.org
== External links == "Corticotropin-releasing Factor Receptors: CRF1". IUPHAR Database of Receptors and Ion Channels. International Union of Basic and Clinical Pharmacology. Archived from the original on 2015-11-20. Retrieved 2008-12-04. Corticotropin-releasing+hormone+receptors at the U.S. National Library of Medicine Medical Subject Headings (MeSH) CRF+receptor+type+1 at the U.S. National Library of Medicine Medical Subject Headings (MeSH) Overview of all the structural information available in the PDB for UniProt: P34998 (Corticotropin-releasing factor receptor 1) at the PDBe-KB.
=== Founding === National Semiconductor was founded in Danbury, Connecticut, by Dr. Bernard J. Rothlein on May 27, 1959, when he and seven colleagues, Edward N. Clarke, Joseph J. Gruber, Milton Schneider, Robert L. Hopkins, Robert L. Koch, Richard R. Rau and Arthur V. Siefert, left their employment at the semiconductor division of Sperry Rand Corporation. The founding of the new company was followed by Sperry Rand filing a lawsuit against National Semiconductor for patent infringement. By 1965, as it was reaching the courts, the preliminaries of the lawsuit had caused the stock value of National to be depressed. The depressed stock values allowed Peter J Sprague to invest heavily in the company with Sprague's family funds. Sprague also relied on further financial backing from a pair of West Coast investment firms and a New York underwriter to take control as the chairman of National Semiconductor. At that time Sprague was 27 years old. Jeffrey S. Young characterized the era as the beginning of venture capitalism. That same year National Semiconductor acquired Molectro. Molectro was founded in 1962 in Santa Clara, California, by J. Nall and D. Spittlehouse, who were formerly employed at Fairchild Semiconductor. The acquisition brought in two experts in linear semiconductor technologies, Robert Widlar and Dave Talbert, who were also formerly employed at Fairchild. The acquisition of Molectro provided National with the technology to launch itself in the fabrication and manufacture of monolithic integrated circuits.
==== Cholestasis ==== Liver injury leads to impairment of bile flow and cases are predominated by itching and jaundice. Histology may show inflammation (cholestatic hepatitis) or it can be bland (without any parenchymal inflammation). On rare occasions, it can produce features similar to primary biliary cirrhosis due to progressive destruction of small bile ducts (vanishing duct syndrome).
Sources: en.wikipedia.org
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.
No regulatory agency has approved it for any indication. It is encountered as a research chemical sold outside pharmaceutical supply chains. Products marketed this way are not subject to the manufacturing and labeling requirements that apply to approved drugs.
Reports describe increased skin pigmentation as well as side effects such as nausea, flushing, and changes to existing moles. Much of the evidence comes from small studies and case reports rather than large trials. The long-term safety profile is therefore uncertain.
It is a synthetic cyclic heptapeptide modelled on alpha-melanocyte-stimulating hormone. A lactam bridge links two side chains, forming a ring that stabilises the molecule against proteolysis. It belongs to the broader melanocortin peptide family.