 | This article may be too technical for most readers to understand.(March 2021) |
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| Formula | C28H32N2O2 |
| Molar mass | 428.576 g·mol−1 |
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BU72 is an extremely potent opioid used in pharmacological research.
BU72 is an agonist for the μ-opioid receptor with exceptionally high binding affinity and potency, comparable to carfentanil. [1] It also has extremely high efficacy, giving a stronger maximal effect than the standard full agonist DAMGO. [2] In animal studies, it was found to be a potent analgesic, with a slow onset and long duration of action. [3] [4]
BU72 was used to produce the first crystal structure of the active μ-opioid receptor, [1] and is now widely used to model the activation process. [5] [6] [7] The stereochemistry has recently been revised, with the phenyl group in the (R) configuration. [8] [9] In the crystal structure, BU72 appears to bond to the receptor covalently, [10] [11] but this seems not to occur in vivo, since the compound binds reversibly, and preventing bond formation has no effect on affinity. [1]
Synthesis: [12]
An agonist is a chemical that activates a receptor to produce a biological response. Receptors are cellular proteins whose activation causes the cell to modify what it is currently doing. In contrast, an antagonist blocks the action of the agonist, while an inverse agonist causes an action opposite to that of the agonist.
A receptor antagonist is a type of receptor ligand or drug that blocks or dampens a biological response by binding to and blocking a receptor rather than activating it like an agonist. Antagonist drugs interfere in the natural operation of receptor proteins. They are sometimes called blockers; examples include alpha blockers, beta blockers, and calcium channel blockers. In pharmacology, antagonists have affinity but no efficacy for their cognate receptors, and binding will disrupt the interaction and inhibit the function of an agonist or inverse agonist at receptors. Antagonists mediate their effects by binding to the active site or to the allosteric site on a receptor, or they may interact at unique binding sites not normally involved in the biological regulation of the receptor's activity. Antagonist activity may be reversible or irreversible depending on the longevity of the antagonist–receptor complex, which, in turn, depends on the nature of antagonist–receptor binding. The majority of drug antagonists achieve their potency by competing with endogenous ligands or substrates at structurally defined binding sites on receptors.
Opioid receptors are a group of inhibitory G protein-coupled receptors with opioids as ligands. The endogenous opioids are dynorphins, enkephalins, endorphins, endomorphins and nociceptin. The opioid receptors are ~40% identical to somatostatin receptors (SSTRs). Opioid receptors are distributed widely in the brain, in the spinal cord, on peripheral neurons, and digestive tract.
Functional selectivity is the ligand-dependent selectivity for certain signal transduction pathways relative to a reference ligand at the same receptor. Functional selectivity can be present when a receptor has several possible signal transduction pathways. To which degree each pathway is activated thus depends on which ligand binds to the receptor. Functional selectivity, or biased signaling, is most extensively characterized at G protein coupled receptors (GPCRs). A number of biased agonists, such as those at muscarinic M2 receptors tested as analgesics or antiproliferative drugs, or those at opioid receptors that mediate pain, show potential at various receptor families to increase beneficial properties while reducing side effects. For example, pre-clinical studies with G protein biased agonists at the μ-opioid receptor show equivalent efficacy for treating pain with reduced risk for addictive potential and respiratory depression. Studies within the chemokine receptor system also suggest that GPCR biased agonism is physiologically relevant. For example, a beta-arrestin biased agonist of the chemokine receptor CXCR3 induced greater chemotaxis of T cells relative to a G protein biased agonist.
The μ-opioid receptors (MOR) are a class of opioid receptors with a high affinity for enkephalins and beta-endorphin, but a low affinity for dynorphins. They are also referred to as μ(mu)-opioid peptide (MOP) receptors. The prototypical μ-opioid receptor agonist is morphine, the primary psychoactive alkaloid in opium and for which the receptor was named, with mu being the first letter of Morpheus, the compound's namesake in the original Greek. It is an inhibitory G-protein coupled receptor that activates the Gi alpha subunit, inhibiting adenylate cyclase activity, lowering cAMP levels.
The nociceptin opioid peptide receptor (NOP), also known as the nociceptin/orphanin FQ (N/OFQ) receptor or kappa-type 3 opioid receptor, is a protein that in humans is encoded by the OPRL1 gene. The nociceptin receptor is a member of the opioid subfamily of G protein-coupled receptors whose natural ligand is the 17 amino acid neuropeptide known as nociceptin (N/OFQ). This receptor is involved in the regulation of numerous brain activities, particularly instinctive and emotional behaviors. Antagonists targeting NOP are under investigation for their role as treatments for depression and Parkinson's disease, whereas NOP agonists have been shown to act as powerful, non-addictive painkillers in non-human primates.
The δ-opioid receptor, also known as delta opioid receptor or simply delta receptor, abbreviated DOR or DOP, is an inhibitory 7-transmembrane G-protein coupled receptor coupled to the G protein Gi/G0 and has enkephalins as its endogenous ligands. The regions of the brain where the δ-opioid receptor is largely expressed vary from species model to species model. In humans, the δ-opioid receptor is most heavily expressed in the basal ganglia and neocortical regions of the brain.
Naltrindole is a highly potent, highly selective delta opioid receptor antagonist used in biomedical research. In May 2012 a paper was published in Nature with the structure of naltrindole in complex with the mouse δ-opioid G-protein coupled receptor, solved by X-ray crystallography.
Dezocine, sold under the brand name Dalgan, is an atypical opioid analgesic which is used in the treatment of pain. It is used by intravenous infusion and intramuscular injection.
DAMGO is a synthetic opioid peptide with high μ-opioid receptor specificity. It was synthesized as a biologically stable analog of δ-opioid receptor-preferring endogenous opioids, leu- and met-enkephalin. Structures of DAMGO bound to the μ opioid receptor reveal a very similar binding pose to morphinans.
In pharmacology and biochemistry, allosteric modulators are a group of substances that bind to a receptor to change that receptor's response to stimuli. Some of them, like benzodiazepines or alcohol, function as psychoactive drugs. The site that an allosteric modulator binds to is not the same one to which an endogenous agonist of the receptor would bind. Modulators and agonists can both be called receptor ligands.
8-Carboxamidocyclazocine (8-CAC) is an opioid analgesic drug related to cyclazocine, discovered by medicinal chemist Mark P. Wentland and co-workers in Cogswell Laboratory at Rensselaer Polytechnic Institute. Similarly to cyclazocine, 8-CAC acts as an agonist at both the μ- and κ-opioid receptors, but has a much longer duration of action than cyclazocine, and does not have μ antagonist activity. Unexpectedly, it was discovered that the phenolic hydroxyl group of cyclazocine could be replaced by a carboxamido group with only slight loss of potency at opioid receptors, and this discovery has subsequently been used to develop many novel opioid derivatives where the phenolic hydroxy group has been replaced by either carboxamide or a variety of larger groups. Due to their strong κ-opioid agonist activity, these drugs are not suited for use as analgesics in humans, but have instead been researched as potential drugs for the treatment of cocaine addiction.
Mitragynine pseudoindoxyl is a rearrangement product of 7-hydroxymitragynine an active metabolite of mitragynine.
Buprenorphine/samidorphan is a combination formulation of buprenorphine and samidorphan which is under development as an add on to antidepressants in treatment-resistant depression (TRD).
PZM21 is an experimental opioid analgesic drug that is being researched for the treatment of pain. It is claimed to be a functionally selective μ-opioid receptor agonist which produces μ-opioid receptor mediated G protein signaling, with potency and efficacy similar to morphine, but with less β-arrestin 2 recruitment. However, recent reports highlight that this might be due to its low intrinsic efficacy, rather than functional selectivity or 'G protein bias' as initially reported. In tests on mice, PZM21 was slightly less potent than morphine or TRV130 as an analgesic, but also had significantly reduced adverse effects, with less constipation than morphine, and very little respiratory depression, even at high doses. This research was described as a compelling example of how modern high-throughput screening techniques can be used to discover new chemotypes with specific activity profiles, even at targets such as the μ-opioid receptor which have already been thoroughly investigated. More recent research has suggested however that at higher doses, PZM21 is capable of producing classic opioid side effects such as respiratory depression and development of tolerance and may have only limited functional selectivity.
β-Funaltrexamine (β-FNA) is an irreversible opioid antagonist that was used to create the first crystal structure of the μ-opioid receptor. Chemically, it is a naltrexone derivative with a methyl-fumaramide group in the 6-position. In addition to its μ-opioid receptor irreversible antagonism, β-FNA is an agonist of the κ-opioid receptor and produces κ-opioid-receptor-mediated analgesic effects in animals. This has limited its usefulness and contributed to the development of methocinnamox as a functionally irreversible antagonist of the μ-opioid receptor with no agonistic actions.
beta-Fuoxymorphamine (β-fuoxymorphamine) is an opioid acting at μ-opioid receptors. It is used experimentally.
Peripherally acting μ-opioid receptor antagonists (PAMORAs) are a class of chemical compounds that are used to reverse adverse effects caused by opioids interacting with receptors outside the central nervous system (CNS), mainly those located in the gastrointestinal tract. PAMORAs are designed to specifically inhibit certain opioid receptors in the gastrointestinal tract and with limited ability to cross the blood–brain barrier. Therefore, PAMORAs do not affect the analgesic effects of opioids within the central nervous system.
SR-17018 is a drug which acts as a biased agonist at the μ-opioid receptor, selective for activation of the G-protein signalling pathway over β-arrestin 2 recruitment. In animal studies it produces analgesic effects but with less respiratory depression and development of tolerance than conventional opioids.
Jan Steyaert is a Belgian bioengineer and molecular biologist. He started his career as an enzymologist but the Steyaertlab is best known for pioneering work on (engineered) nanobodies for applications in structural biology, omics and drug design. He is full professor and teaches biochemistry at the Vrije Universiteit Brussel and Director of the VIB-VUB Center for Structural Biology, one of the Research Centers of the Vlaams Instituut voor Biotechnologie (VIB). He was involved in the foundation of three spin-off companies: Ablynx, Biotalys, and Confo Therapeutics.
