If you have been reading about cyclic heptapeptide and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Last reviewed on 2025-09-23. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Chemical class | Synthetic cyclic heptapeptide | Melanocortin receptor agonist |
| Molecular formula | C50H69N15O9 | Neutral form, mass near 1024.2 g/mol |
| Primary targets | MC1R, MC3R, MC4R, MC5R | Binding is non-selective across subtypes |
| Related compounds | Alpha-MSH, melanotan I, afamelanotide | Structurally or functionally related peptides |
| Common abbreviations | MT-II, MT-2 | Naming in the literature is not uniform |
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.
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.
Enzyme assays are laboratory procedures that measure the rate of enzyme reactions. Since enzymes are not consumed by the reactions they catalyse, enzyme assays usually follow changes in the concentration of either substrates or products to measure the rate of reaction. There are many methods of measurement. Spectrophotometric assays observe the change in the absorbance of light between products and reactants; radiometric assays involve the incorporation or release of radioactivity to measure the amount of product made over time. Spectrophotometric assays are most convenient since they allow the rate of the reaction to be measured continuously. Although radiometric assays require the removal and counting of samples (i.e., they are discontinuous assays), they are usually extremely sensitive and can measure very low levels of enzyme activity. An analogous approach is to use mass spectrometry to monitor the incorporation or release of stable isotopes as the substrate is converted into product. Occasionally, an assay fails and approaches are essential to resurrect a failed assay. The most sensitive enzyme assays use lasers focused through a microscope to observe changes in single enzyme molecules as they catalyse their reactions. These measurements either use changes in the fluorescence of cofactors during an enzyme's reaction mechanism, or of fluorescent dyes added onto specific sites of the protein to report movements that occur during catalysis.
==== American Federation of Government Employees v. Trump ==== A lawsuit was filed on February 6, 2025, by the American Foreign Service Association and the American Federation of Government Employees in the US District Court for the District of Columbia, requesting a temporary restraining order and preliminary injunction against the administration, claiming that it violated separation of powers, the Take Care Clause of the Constitution, and the Administrative Procedure Act and requesting that all attempts to shut down the agency be halted, all recent actions be reversed, and a new acting director be appointed. The following day, U.S. District Judge Carl Nichols, nominated by President Trump in 2019, stated from the bench that he would enter in a "temporary restraining order", pausing the plan to put thousands of employees on leave and pausing the accelerated removal of workers from their posts abroad. On February 21, 2025, Judge Nichols cleared the way for the Trump administration to move forward with pulling thousands of USAID staffers off the job in the United States and around the world, as part of an administration plan to also provide those abroad with a 30-day deadline to move back to the U.S. at government expense. Nichols had previously argued that Trump's actions threaten the safety of USAID workers abroad because many are deployed in unstable regions.
The FDA also said that coincidental natural mood variation is the most likely explanation for the apparent worsening of depression after the switch from Wellbutrin XL to Budeprion XL. After several years of denying patient reports, in 2012 the FDA reversed this opinion, announcing that "Budeprion XL 300 mg fails to demonstrate therapeutic equivalence to Wellbutrin XL 300 mg." The FDA did not test the bioequivalence of any of the other generic versions of Wellbutrin XL 300 mg, but requested that the four manufacturers submit data on this question to the FDA by March 2013. As of October 2013, the FDA has made determinations on the formulations from some manufacturers not being bioequivalent. In 2004, Ranbaxy was revealed to have been falsifying data regarding the generic drugs they were manufacturing. As a result, 30 products were removed from US markets and Ranbaxy paid $500 million in fines. The FDA investigated many Indian drug manufacturers after this was discovered, and as a result at least 12 companies have been banned from shipping drugs to the US. In 2017, The European Medicines Agency recommended suspension of a number of nationally approved medicines for which bioequivalence studies were conducted by Micro Therapeutic Research Labs in India, due to inspections identifying misrepresentation of study data and deficiencies in documentation and data handling.
Sources: en.wikipedia.org
Electron capture: the decay energy is 0.93 MeV and the decay product is uranium-236. This usually decays (with a half-life of 23 million years) to thorium-232. Beta emission: the decay energy is 0.48 MeV and the decay product is plutonium-236. This usually decays (half-life 2.8 years) to uranium-232, which usually decays (half-life 69 years) to thorium-228, which decays in a few years to lead-208. Alpha emission: the decay energy is 5.007 MeV and the decay product is protactinium-232. This decays with a half-life of 1.3 days to uranium-232. Neptunium-236 is a fissile material; it has an estimated critical mass of 6.79 kg (15.0 lb), though precise experimental data is not available (as sufficient material for criticality is not). 236Np is produced in small quantities via the (n,2n) and (γ,n) capture reactions of 237Np, however, it is nearly impossible to separate in any significant quantities from its parent 237Np. It is for this reason that despite its low critical mass and high neutron cross section, it has not been researched extensively as a nuclear fuel in weapons or reactors. Nevertheless, 236Np has been considered for use in mass spectrometry and as a radioactive tracer, because it decays predominantly by beta emission with a long half-life. Several alternative production routes for this isotope have been investigated, namely those that reduce isotopic separation from 237Np or the isomer 236mNp. The most favorable reactions to accumulate 236Np were shown to be proton and deuteron irradiation of uranium-238.
== History == Zopiclone was developed and first introduced in 1986 by Rhône-Poulenc S.A., now part of Sanofi, the main worldwide manufacturer. Initially, it was promoted as an improvement on benzodiazepines, which has since been disproven. On April 4, 2005, the U.S. Drug Enforcement Administration listed zopiclone under schedule IV, due to evidence that the drug has addictive properties similar to benzodiazepines. Zopiclone, as traditionally sold worldwide, is a racemic mixture of two stereoisomers, only one of which is active. In 2005, the pharmaceutical company Sepracor of Marlborough, Massachusetts, began marketing the active stereoisomer eszopiclone under the name Lunesta in the United States. This had the consequence of placing what is a generic drug in most of the world under patent control in the United States. Generic forms of Lunesta have since become available in the United States. Zopiclone is currently available off-patent in a number of European countries, Brazil, Canada, Hong Kong, and New Zealand. The eszopiclone/zopiclone difference is in the dosage—the strongest eszopiclone dosage contains 3 mg of the therapeutic stereoisomer, whereas the highest zopiclone dosage (10 mg) contains 5 mg of the active stereoisomer.
=== Sources === JYB = Jewish Year Book Bell, John; Millar, Victoria (19 May 2011). "Eleanor Farjeon". Oxford Dictionary of National Biography (online ed.). Oxford University Press. doi:10.1093/ref:odnb/33079. Brown, Andrew (2005). J D Bernal—The Sage of Science. Oxford: Oxford University Press. ISBN 0-19-851544-8. Grove, Jack (27 March 2013). "Tribunal slams academic for bringing anti-Semitism case". Times Higher Education. Retrieved 16 March 2020. Johns, Francis A (1983). "Manifestations of Arthur Waley: Some Bibliographical and Other Notes" (PDF). The British Library Journal. 9 (2): 171–184.
Sources: en.wikipedia.org
It is a synthetic cyclic heptapeptide and a non-selective melanocortin receptor agonist. Structurally it is modelled on alpha-melanocyte-stimulating hormone, a peptide that occurs naturally in the body.
Activation of MC1R increases pigment synthesis independently of ultraviolet exposure, which is the mechanism usually cited for darkening without sun exposure. Ultraviolet light still influences skin response through separate biological pathways.
Because the peptide binds several melanocortin receptor subtypes, its effects are not confined to pigmentation. This complicates interpretation of both intended and unintended outcomes reported in studies.
It is a synthetic cyclic heptapeptide analogue of alpha-melanocyte-stimulating hormone, containing seven amino acids with a lactam ring and a D-configured phenylalanine residue. It is supplied as a lyophilised powder for laboratory research.