A practical reference on cyclic heptapeptide: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
This page was last updated on 2026-05-27 and is reviewed periodically as new material appears.
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 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controlled human data on melanotan-2 remain sparse, and much of what circulates online derives from small studies or unpublished reports.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 |
|---|---|---|
| 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 |
Melanocortin receptors comprise five subtypes with distinct tissue distributions and functions. Melanotan-2 is described in the literature as a non-selective agonist that engages several of these subtypes, including MC1R, MC3R, MC4R, and MC5R. MC1R is the subtype most directly linked to melanin production in skin cells. Because the compound is not subtype-selective, its observed effects in experimental settings are generally attributed to activity across multiple receptor pathways rather than to a single target.
Melanotan-2 is a synthetic linear peptide built from seven amino acids arranged in a short chain. Its sequence is commonly written as Ac-Nle-Asp-His-D-Phe-Arg-Trp-Lys-NH2, which includes a modified N-terminus and an amidated C-terminus. The molecule belongs to the melanocortin family and acts as a receptor agonist. Structural features such as the D-phenylalanine residue and the Nle substitution are associated with increased stability against enzymatic degradation relative to the natural parent peptide.
The compound emerged from research programs in the 1980s that examined analogues of alpha-melanocyte-stimulating hormone for pigmentation and photoprotection. Investigators modified the native sequence to extend activity duration and potency. A related analogue, afamelanotide, was developed within the same broad line of inquiry and eventually gained approval in certain jurisdictions for a rare light-sensitivity condition. Melanotan-2 itself did not progress through the same regulatory route and has no approved therapeutic indication.
Two structural changes distinguish the synthetic peptide from the natural hormone. A norleucine residue replaces methionine at one position, and a D-configured phenylalanine replaces the natural L-form at another. Both substitutions slow enzymatic breakdown, which extends the molecule's persistence relative to the parent hormone. The lactam bridge further constrains the backbone into a stable conformation. These features are standard design strategies in peptide chemistry and are not unique to this compound; they appear across many research peptides built for improved stability.
The compound was developed in the late 1980s and early 1990s by academic researchers investigating melanocortin signaling and pigmentation. Early work explored whether synthetic analogs could reproduce effects of the natural hormone under controlled conditions. The molecule never advanced through the full regulatory pathway required for approval as a medicine. From the mid-2000s onward it appeared in unregulated consumer markets, often distributed through informal channels. That gap between research origins and commercial availability shapes how the compound is discussed today.
=== South Africa === In South Africa learnerships to qualify as a Phlebotomy Technician are offered by many public and private educational institutions as well as by private academies owned up by pathology laboratories (such as Ampath Laboratories, Lancet, PathCare) and healthcare service providers (such as Netcare, South African National Blood Service). Some of the larger retail pharmacy chains offering in-store clinical services (such as Clicks, Dis-Chem) also provide training for aspirant phlebotomists. Certification can be obtained from a number of examination and testing institutions. To work as a phlebotomist in South Africa, registration with the Health Professions Council of South Africa (HPCSA) is required.
== External links == Enkephalins at the U.S. National Library of Medicine Medical Subject Headings (MeSH) Nosek, Thomas M. "Section 6/6ch2/s6ch2_36". Essentials of Human Physiology. Archived from the original on 2016-03-24.
In a clinical trial, the rate of systolic orthostatic hypotension was 21% versus 9% with placebo and the rate of diastolic orthostatic hypotension was 12% versus 4% with placebo in people with Parkinson's disease taking the ODT form of selegiline. The risk of hypotension is greater at the start of treatment and in the elderly (3% vs. 0% with placebo). The rate of hypotension or orthostatic hypotension with the selegiline patch was 2.2% versus 0.5% with placebo in clinical trials of people with depression. Significant orthostatic blood pressure changes (≥10 mm Hg decrease) occurred in 9.8% versus 6.7% with placebo, but most of these cases were asymptomatic and heart rate was unchanged. The rates of other orthostatic hypotension-related side effects in this population were dizziness or vertigo 4.9% versus 3.1% with placebo and fainting 0.5% versus 0.0% with placebo. It is said that orthostatic hypotension is rarely seen with the selegiline transdermal patch compared to oral MAOIs. Caution is advised against rapidly rising after sitting or lying, especially after prolonged periods or at the start of treatment, as this can result in fainting. Falls are of particular concern in the elderly. MAOIs like selegiline may lower blood pressure by increasing dopamine levels and activating dopamine receptors, by increasing levels of the false neurotransmitter octopamine, and/or by other mechanisms. Meta-analyses published in the 1990s found that the addition of selegiline to levodopa increased mortality in people with Parkinson's disease.
10 February – An analysis of Outer London's Mini-Hollands active transport infrastructures indicates Low Traffic Neighbourhoods are highly effective and cost-efficient measures in terms of health economic benefits. 12 February – The first detection of water molecules on the surface of asteroids is announced, following spectral analysis of 7 Iris and 20 Massalia, two large main-belt objects.
Sources: en.wikipedia.org
=== United States === On 7 February 2026, Lance Cpl. Chukwuemeka E. Oforah, a US Marine, died in a non-combat incident after falling overboard from the amphibious assault ship USS Iwo Jima (LHD-7) while operating in the Caribbean Sea. Search and rescue efforts were unsuccessful. This is the only reported US military fatality during Operation Southern Spear.
==== Molecular fingerprints ==== A molecular fingerprint is a binary vector, where each position corresponds to a specific molecular property. In this representation, a given position X may encode the presence or absence of a particular substructure, with '1' indicating presence and '0' indicating absence. Various types of molecular fingerprints exist, including PubChem CACTVS fingerprints, Klekota-Roth fingerprints, MACCS fingerprints, and Extended-Connectivity Fingerprints (ECFP). A molecular fingerprint can be deterministically computed from a given molecular structure. Different molecular structures may yield the same molecular fingerprint.
== Chemistry == Omeprazole contains a tricoordinated sulfinyl sulfur in a pyramidal structure and therefore can exist as either the (S)- or (R)-enantiomers. Omeprazole is a racemate, an equal mixture of the two.
Beans, lima beans, yucca, yams, arracacia, caigua, pumpkin, and squash were available depending on the region. Wild vegetables eaten included cochayuyo, watercress, and cattail. Fruits consumed included lucuma, pacay, guava, and cucumbers. Meat came from either domesticated animals such as llamas, alpacas, and guinea pigs, or wild animals such as guanacos, vicuñas, deer, viscacha, partridges, doves, and ducks. Fish was also available. These foods would have been cooked and served in various ways. While on campaign, Incan armies made frequent use of dehydrated foods that could be prepared, preserved, and transported in sufficient quantities. During marches through desert regions, soldiers relied on a combination of dehydrated foods and fresh meat from the llamas accompanying the army as a means of transport.
This was the first observation of a nuclear reaction, that is, a reaction in which particles from one decay are used to transform another atomic nucleus. It also offered a new way to study the nucleus. Rutherford and James Chadwick then used alpha particles to "disintegrate" boron, fluorine, sodium, aluminum, and phosphorus before reaching a limitation associated with the energy of his alpha particle source. Eventually, in 1932, a fully artificial nuclear reaction and nuclear transmutation was achieved by Rutherford's colleagues Ernest Walton and John Cockcroft, who used artificially accelerated protons against lithium-7, to split this nucleus into two alpha particles. The feat was popularly known as "splitting the atom", and would win them the 1951 Nobel Prize in Physics for "Transmutation of atomic nuclei by artificially accelerated atomic particles", although it was not the nuclear fission reaction later discovered in heavy elements. English physicist James Chadwick discovered the neutron in 1932. Chadwick used an ionization chamber to observe protons knocked out of several elements by beryllium radiation, following up on earlier observations made by Joliot-Curies.
Sources: en.wikipedia.org
The general structure of the endoplasmic reticulum is a network of membranes called cisternae. These sac-like structures are held together by the cytoskeleton. The phospholipid membrane encloses the cisternal space (or lumen), which is continuous with the perinuclear space but separate from the cytosol. The functions of the endoplasmic reticulum can be summarized as the synthesis and export of proteins and membrane lipids, but varies between ER and cell type and cell function. The quantity of both rough and smooth endoplasmic reticulum in a cell can slowly interchange from one type to the other, depending on the changing metabolic activities of the cell. Transformation can include embedding of new proteins in membrane as well as structural changes. Changes in protein content may occur without noticeable structural changes.
An early-20th-century form of quackery was the treatment of maladies in a radiotorium. It was a small, sealed room for patients to be exposed to radon for its "medicinal effects". The carcinogenic nature of radon due to its ionizing radiation became apparent later. Radon's molecule-damaging radioactivity has been used to kill cancerous cells, but it does not increase the health of healthy cells. The ionizing radiation causes the formation of free radicals, which results in cell damage, causing increased rates of illness, including cancer. Exposure to radon has been suggested to mitigate autoimmune diseases such as arthritis in a process known as radiation hormesis. As a result, in the late 20th century and early 21st century, "health mines" established in Basin, Montana, attracted people seeking relief from health problems such as arthritis through limited exposure to radioactive mine water and radon. The practice is discouraged because of the well-documented ill effects of high doses of radiation on the body. Radioactive water baths have been applied since 1906 in Jáchymov, Czech Republic, but even before radon discovery they were used in Bad Gastein, Austria. Radium-rich springs are also used in traditional Japanese onsen in Misasa, Tottori Prefecture. Drinking therapy is applied in Bad Brambach, Germany, and during the early 20th century, water from springs with radon in them was bottled and sold (this water had little to no radon in it by the time it got to consumers due to radon's short half-life).
Stimulants such as epinephrine, theophylline, and salbutamol orally have been used to treat asthma, but inhaled adrenergic drugs are now preferred due to less systemic side effects. Pseudoephedrine is used to relieve nasal or sinus congestion caused by the common cold, sinusitis, allergic rhinitis, and other respiratory allergies; it is also used to relieve ear congestion caused by ear inflammation or infection.
Nicotine replacement therapy (NRT) products, including gums, patches, and lozenges, deliver the compound in slower, lower doses that are less addictive and are used medically to help people quit smoking. Synthetic derivatives of nicotine, such as varenicline, act as partial agonists at nicotinic receptors and are also used as smoking cessation aids. Nicotine itself is not classified as a carcinogen by either the International Agency for Research on Cancer or the Surgeon General of the United States. At high doses it can cause nicotine poisoning and respiratory paralysis. Nicotine is also a known teratogen, associated with adverse developmental effects during pregnancy, and may impair adolescent neurodevelopment, though the extent of this effect in humans remains debated.
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 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.