The short version of cyclic heptapeptide fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2026-07-10. Anything still debated is marked as such rather than presented as settled.
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 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.
| 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, 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.
Etoetonitazene is a benzimidazole derivative with opioid effects, first developed in the 1950s as part of the research that led to better-known compounds such as etonitazene. It is an analogue of etonitazene where the ethoxy sidechain has been extended to ethoxyethoxy. It is less potent than other benzimidazole class opioids, but is still a potent mu opioid receptor agonist with around 50x the potency of morphine, and has been sold as a designer drug since around 2022.
== Geography == Enewetak Atoll formed atop a seamount. The seamount was formed in the late Cretaceous. This seamount is now about 1,400 meters (4,600 ft) below sea level. It is made of basalt, and its depth is due to a general subsidence of the entire region and not because of erosion. Enewetak has a mean elevation above sea level of 3 meters (9.8 ft).
== Cause == Risk factors for allergies can be placed in two broad categories: host and environmental factors. Host factors include heredity, sex, race, and age, with heredity being by far the most significant. However, there has been a recent increase in the incidence of allergic disorders that cannot be explained by genetic factors alone. Four major environmental candidates are alterations in exposure to infectious diseases during early childhood, environmental pollution, allergen levels, and dietary changes.
Sources: en.wikipedia.org
This is normally achieved through regular blood tests, although continuous blood sugar testing equipment (Continuous Glucose Monitors or CGMs) are now becoming available which could help to refine this balancing act once widespread usage becomes common.
==== 2014 ==== In March 2014, Novaya Gazeta reported that 1st platoon of the military unit entered South Ossetia from North Ossetia on the night of 7 August 2008 to defend the Roki tunnel. At 4:00 AM on 7 August, one soldier was killed on the firing position after two shots were heard. According to the official version, the cause of death was suicide. However, the soldier's family and comrades' testimonies dispute the official cause of death. In August 2014, Anatoly Khrulyov, the commander of the 58th Army, said in an interview that at 12:03 a.m. on the night of 8 August 2008, he ordered to open the "alarm" packet containing the operational objective of the 58th Army and the plan to reinforce the peacekeepers in South Ossetia prepared in advance before August 2008. Khruloyv said that Russian troops approached the Gupta bridge in South Ossetia in four hours after "the declaration of war" by Georgia and engaged Georgian troops. Khrulyov said that if he had not contacted the General Staff during the war and received new orders, the 58th Army would have taken Tbilisi.
== Titanium dioxide and zinc oxide nanoparticles in sunscreen == Sunscreens are utilized to secure the skin from the destructive impacts of ultraviolet radiation from the sun. UVB (290-320 nm) together with UVA-2 (320–340 nm) and UVA-1 (340–400 nm) cause organic and metabolic reactions in the skin. Titanium dioxide (TiO2) and zinc oxide (ZnO) minerals are often utilized in sunscreens as inorganic physical sun blockers owing to their absorption of light in the UV range. As TiO2 is proven to be more effective for blocking UVB and ZnO in the UVA range, the mix of these particles guarantees a broad-band UV shield. To solve the cosmetic disadvantage of these opaque sunscreens, TiO2 and ZnO nanoparticles have been used as a replacement for TiO2 and ZnO microparticles. Since the surface area to volume proportion of particles increases as the particle measurement diminishes, nanoparticles (NPs), ie, nano objects with all dimensions in the nanoscale, might be increasingly (bio)reactive than typical mass materials. When particles become smaller than 100 nm, novel optical attributes develop, owing to discrete nature of nanoparticle optical energy levels. Pat et al., for instance, measured a 0.15 eV blue shift for 4.7 nm TiO2 nanoparticles relative to the bulk material counterpart. When particles become smaller than the ideal light dispersing size (roughly half of the wavelength) visible light is transmitted and the particles appear transparent. This phenomenon explains the cosmetically undesired opaqueness of inorganic sunscreens and makes the utilization of NPs monetarily appealing.
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.
No. It is a synthetic analogue carrying four amino acid changes, a lactam ring and an amidated C-terminus. The natural hormone is a linear thirteen-amino-acid peptide processed from proopiomelanocortin.