This is a working overview of lactam bridge, written for readers who want more than a one-paragraph summary but less than a textbook.
This page was last updated on 2026-02-20 and is reviewed periodically as new material appears.
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.
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.
Melanotan-2 is a synthetic peptide designed as an analog of alpha-melanocyte-stimulating hormone, a signaling molecule produced in the pituitary and skin. Its structure is a linear chain of seven amino acids that folds into a ring through an internal lactam bridge joining two side chains. The compound is sometimes written as MT-II or MEL-2 in informal and commercial contexts. It belongs to the melanocortin peptide family, a group of short signaling molecules that share a conserved core sequence recognized by melanocortin receptors.
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C50H69N15O9 | Cyclic heptapeptide, C-terminally amidated |
| Approximate molecular mass | 1024 Da | Monoisotopic mass of the free peptide |
| Appearance | White to off-white powder | Typically supplied as a lyophilised solid |
| Solubility class | Soluble in water and polar solvents | Also dissolves in neutral aqueous buffer |
| Common synonyms | Melanotan II, MT-II, MT-2 | Described as a melanocortin agonist in early literature |
Receptor studies place melanotan-2 among non-selective melanocortin agonists, binding MC1R, MC3R, MC4R and MC5R rather than a single subtype. Activation of MC1R on cutaneous melanocytes raises tyrosinase activity and shifts pigment synthesis toward eumelanin, which is darker and more photostable than pheomelanin. Central receptors, particularly MC4R, are associated with appetite suppression and with reported effects on sexual function. Because subtype selectivity is low, the same molecule engages pigment, metabolic and vascular pathways at once, and this breadth is a common explanation offered for the range of adverse events described in user reports.
No regulatory authority has approved melanotan-2 for human use, and several countries classify it as a prescription-only or controlled substance, which restricts lawful supply. Material sold online is generally labelled as a research chemical and is not required to meet pharmaceutical standards of identity or purity. Published human data consist mainly of small uncontrolled studies, case reports and adverse-event notifications, so the evidence base is descriptive rather than confirmatory. Whether repeated melanocyte stimulation alters long-term naevus behaviour remains an open question that no completed trial has resolved.
Melanotan-2 is a synthetic cyclic heptapeptide designed as a structural analogue of alpha-melanocyte-stimulating hormone, the endogenous tridecapeptide that regulates pigment production. Two modifications distinguish it from the natural hormone: norleucine replaces methionine at the N-terminus, which limits oxidation, and a D-phenylalanine substitution raises receptor affinity. The ring is closed through an aspartate-lysine lactam bridge, giving the molecule a constrained conformation. The free base has a molecular mass near 1024 daltons, and commercial material is usually supplied as an acetate salt. It appears in the literature as a research peptide rather than an approved therapeutic agent.
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.
== History == The All-China Federation of Supply and Marketing Cooperatives traces its origins to the former Central Cooperation Administration, founded by central government in November 1949. The first representative conference of all cooperative workers in China was held in July 1950, and the conference passed documents such as the "Law of the People's Republic of China on Cooperatives (Draft)" (中华人民共和国合作社法（草案）) and the "Articles of Association of the All China Federation of Cooperatives (Draft)" (中华全国合作社联合总社章程（草案）). The All-China Federation of Cooperatives (中华全国合作社联合总社) was established, which unified the leadership and management of supply and marketing, production, fisheries, handicrafts, consumption, and credit cooperatives throughout the whole country. The All-China Federation of Supply and Marketing Cooperatives became a member of the International Cooperative Alliance (ICA) on 14 August 1985.
On a pressure/temperature phase diagram (see figure), there are curves separating solid from vapor, vapor from liquid, and liquid from solid. These meet at a single point called the triple point, where all three phases can coexist. The triple point is at a temperature of 273.16 K (0.01 °C; 32.02 °F) and a pressure of 611.657 pascals (0.00604 atm; 0.0887 psi); it is the lowest pressure at which liquid water can exist. Until 2019, the triple point was used to define the Kelvin temperature scale. The water/vapor phase curve terminates at 647.096 K (373.946 °C; 705.103 °F) and 22.064 megapascals (3,200.1 psi; 217.75 atm). This is known as the critical point. At higher temperatures and pressures the liquid and vapor phases form a continuous phase called a supercritical fluid. It can be gradually compressed or expanded between gas-like and liquid-like densities; its properties (which are quite different from those of ambient water) are sensitive to density. For example, for suitable pressures and temperatures it can mix freely with nonpolar compounds, including most organic compounds. This makes it useful in a variety of applications including high-temperature electrochemistry and as an ecologically benign solvent or catalyst in chemical reactions involving organic compounds. In Earth's mantle, it acts as a solvent during mineral formation, dissolution and deposition.
=== Books === In September 2019, Sinclair published Lifespan: Why We Age – and Why We Don't Have To co-written with journalist Matthew LaPlante and translated into 18 languages. This was also released as an audiobook on Audible and read by Sinclair. Sinclair broadly discusses his longevity practices on social media and includes them in his book. They include daily doses of nicotinamide mononucleotide (NMN) and resveratrol, which Sinclair claims are activators of SIRT1.
=== Substrate-like inhibitors === Substrate-like inhibitors (Figure 4) are more common than the non-substrate-likes. They bind either covalently or non-covalently and have a basic structure where the P1-substituent occupies the S1-pocket and the P2-substituent occupies the S2-pocket. Usually they contain a proline mimetic that occupies the S1-pocket. Large substituents on the 2-cyanopyrrolidine ring are normally not tolerated since the S1-pocket is quite small. Since DPP-4 is identical with the T-cell activation marker CD26 and DPP-4 inhibitors are known to inhibit T-cell proliferation, these compounds were initially thought to be potential immunomodulators. When the function against type 2 diabetes was discovered, the cyanopyrrolidines became a highly popular research material. A little later vildagliptin and saxagliptin, which are the most developed cyanopyrrolidine DPP-4 inhibitors to date, were discovered.
The French are also known for their violet syrup, most commonly made from an extract of violets. In the United States, this French violet syrup is used to make violet scones and marshmallows. Viola essence flavours the liqueurs Creme Yvette, Creme de Violette, and Parfait d'Amour. It is also used in confectionery, such as Parma Violets and C. Howard's Violet candies.
Sources: en.wikipedia.org
The DNA passing through the nanopore changes its ion current. This change is dependent on the shape, size and length of the DNA sequence. Each type of the nucleotide blocks the ion flow through the pore for a different period of time. The method does not require modified nucleotides and is performed in real time. Nanopore sequencing is referred to as "third-generation" or "long-read" sequencing, along with SMRT sequencing. Early industrial research into this method was based on a technique called 'exonuclease sequencing', where the readout of electrical signals occurred as nucleotides passed by alpha(α)-hemolysin pores covalently bound with cyclodextrin. However the subsequent commercial method, 'strand sequencing', sequenced DNA bases in an intact strand. Two main areas of nanopore sequencing in development are solid state nanopore sequencing, and protein based nanopore sequencing. Protein nanopore sequencing utilizes membrane protein complexes such as α-hemolysin, MspA (Mycobacterium smegmatis Porin A) or CssG, which show great promise given their ability to distinguish between individual and groups of nucleotides. In contrast, solid-state nanopore sequencing utilizes synthetic materials such as silicon nitride and aluminum oxide and it is preferred for its superior mechanical ability and thermal and chemical stability. The fabrication method is essential for this type of sequencing given that the nanopore array can contain hundreds of pores with diameters smaller than eight nanometers.
=== Glyoxylate cycle === The glyoxylate cycle is a variant of the citric acid cycle. It is an anabolic pathway occurring in plants and bacteria utilizing the enzymes isocitrate lyase and malate synthase. Some intermediate steps of the cycle are slightly different from the citric acid cycle; nevertheless oxaloacetate has the same function in both processes. This means that oxaloacetate in this cycle also acts as the primary reactant and final product. In fact the oxaloacetate is a net product of the glyoxylate cycle because its loop of the cycle incorporates two molecules of acetyl-CoA.
Many psychedelics are classified under Schedule I of the United Nations Convention on Psychotropic Substances of 1971 as drugs with the greatest potential to cause harm and no acceptable medical uses. In addition, many countries have analogue laws; for example, in the United States, the Federal Analogue Act of 1986 automatically forbids any drugs sharing similar chemical structures or chemical formulas to prohibited substances if sold for human consumption. In July 2022, though, under the United States Food and Drug Administration, the drug psilocybin was on track to be approved of as a treatment for depression, and MDMA as a treatment for post-traumatic stress disorder. U.S. states such as Oregon and Colorado have also instituted decriminalization and legalization measures for accessing psychedelics and states like New Hampshire are attempting to do the same. J.D. Tuccille argues that increasing rates of use of psychedelics in defiance of the law are likely to result in more widespread legalization and decriminalization of access to the substances in the United States (as has happened with alcohol and cannabis).
He was a consistent performer in an inconsistent season for the Bombers, polling 16 Brownlow votes from a total of 43 received by Essendon players, including a three-vote game in his 100th AFL game, finishing equal-seventh in the 2010 Brownlow Medal count, and having the highest number of votes for a player from a team finishing outside the final eight. Watson was once again awarded the Crichton Medal, earning 291 points, which was 50 points clear of runner-up Heath Hocking. Watson had a relatively good season in 2011 despite missing six weeks with a hamstring injury, earning 15 Brownlow votes and finishing runner-up in the Crichton Medal, losing out to up-and-coming third-year midfielder David Zaharakis. Watson completed an outstanding 2012 season by winning the Brownlow Medal with 30 votes (though he was later ruled ineligible after being suspended during the Essendon Football Club supplements saga). Along with his third Crichton Medal, he also won a handful of other accolades, including the AFLPA best captain award, the Lou Richards Medal and selection in the 2012 All-Australian team as the centreman. Watson missed three weeks with a broken collarbone in 2013, but had another consistent season, earning 17 Brownlow votes, finishing runner-up in the Crichton Medal to former St Kilda utility (and later successor as captain) Brendon Goddard, and being named on the interchange in the 2013 All-Australian team. Between 2006 and 2013, Watson finished all but one season in the top two for votes for the Crichton Medal.
Sources: en.wikipedia.org
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.
Afamelanotide is the linear analogue [Nle4-D-Phe7]-alpha-MSH, sometimes called melanotan I, while melanotan II is cyclic and carries three further substitutions. The two are distinct molecules and are not interchangeable in analytical testing.
Binding to the four melanocortin receptor subtypes is well documented in vitro. The relative contribution of each subtype to whole-body effects in humans is far less certain.
It is a synthetic seven-amino-acid peptide modeled on alpha-melanocyte-stimulating hormone. It carries two non-natural substitutions and a cyclic bridge that increase its stability relative to the natural hormone. It circulates as a research chemical and is not an approved medicine.