Cannabinoids are several structural classes of compounds found in the cannabis plant primarily and most animal organisms or as synthetic compounds. The most notable cannabinoid is the phytocannabinoid tetrahydrocannabinol (THC) (delta-9-THC), the primary psychoactive compound in cannabis. Cannabidiol (CBD) is also a major constituent of temperate cannabis plants and a minor constituent in tropical varieties. At least 100 distinct phytocannabinoids have been isolated from cannabis, although only four have been demonstrated to have a biogenetic origin. It was reported in 2020 that phytocannabinoids can be found in other plants such as rhododendron, licorice and liverwort, and earlier in Echinacea.
Cannabinoid receptors, located throughout the body, are part of the endocannabinoid system of vertebrates– a class of cell membrane receptors in the G protein-coupled receptor superfamily. As is typical of G protein-coupled receptors, the cannabinoid receptors contain seven transmembrane spanning domains. Cannabinoid receptors are activated by three major groups of ligands:
Cannabinol (CBN) is a mildly psychoactive phytocannabinoid that acts as a low affinity partial agonist at both CB1 and CB2 receptors. This activity at CB1 and CB2 receptors constitutes interaction of CBN with the endocannabinoid system (ECS).
WIN 55,212-2 is a chemical described as an aminoalkylindole derivative, which produces effects similar to those of cannabinoids such as tetrahydrocannabinol (THC) but has an entirely different chemical structure.
Cannabinoid receptor 1 (CB1), is a G protein-coupled cannabinoid receptor that in humans is encoded by the CNR1 gene. And discovered, by determination and characterization in 1988, and cloned in 1990 for the first time. The human CB1 receptor is expressed in the peripheral nervous system and central nervous system. It is activated by endogenous cannabinoids called endocannabinoids, a group of retrograde neurotransmitters that include lipids, such as anandamide and 2-arachidonoylglycerol; plant phytocannabinoids, such as docosatetraenoylethanolamide found in wild daga, the compound tetrahydrocannabinol which is an active constituent of the psychoactive drug cannabis; and synthetic analogs of tetrahydrocannabinol. CB1 is antagonized by the phytocannabinoid tetrahydrocannabivarin at low doses and at higher doses, it activate the CB1 receptor as an agonist, but with less potency than tetrahydrocannabinol.
The cannabinoid receptor 2(CB2), is a G protein-coupled receptor from the cannabinoid receptor family that in humans is encoded by the CNR2 gene. It is closely related to the cannabinoid receptor 1 (CB1), which is largely responsible for the efficacy of endocannabinoid-mediated presynaptic-inhibition, the psychoactive properties of tetrahydrocannabinol (THC), the active agent in cannabis, and other phytocannabinoids. The principal endogenous ligand for the CB2 receptor is 2-Arachidonoylglycerol (2-AG).
AM-411 is an analgesic drug that is a cannabinoid agonist. It is a derivative of Δ8-THC substituted with an adamantyl group at the 3-position, demonstrating that the binding pocket for the alkyl chain at this position can accommodate significant bulk.
AM-919 is an analgesic drug which is a cannabinoid receptor agonist. It is a derivative of HU-210 which has been substituted with a 6β-(3-hydroxypropyl) group. This adds a "southern" aliphatic hydroxyl group to the molecule as seen in the CP-series of nonclassical cannabinoid drugs, and so AM-919 represents a hybrid structure between the classical dibenzopyran and nonclassical cannabinoid families.
AM-938 (part of the AM cannabinoid series) is an analgesic drug which is a cannabinoid receptor agonist. It is a derivative of HU-210 which has been substituted with a 6β-(3-hydroxyprop-1-ynyl) group. This adds a "southern" aliphatic hydroxyl group to the molecule as seen in the CP-series of nonclassical cannabinoid drugs, and so AM-938 represents a hybrid structure between the classical and nonclassical cannabinoid families, with the 6-hydroxyalkyl chain rigidified with a triple bond. This gives AM-938 a greater degree of selectivity, so while it is still a potent agonist at both CB1 and CB2, it is reasonably selective for CB2, with a Ki of 0.3 nM at CB2 and 1.2 nM at CB1, a selectivity of around four-fold.
AM-4030 is an analgesic drug which is a cannabinoid receptor agonist. It is a derivative of HU-210 which has been substituted with a 6β-((E)-3-hydroxyprop-1-enyl) group. This adds a "southern" aliphatic hydroxyl group to the molecule as seen in the CP-series of nonclassical cannabinoid drugs, and so AM-4030 represents a hybrid structure between the classical and nonclassical cannabinoid families, with the 6-hydroxyalkyl chain rigidified with a double bond with defined stereochemistry. This gives AM-4030 a greater degree of selectivity, so while it is still a potent agonist at both CB1 and CB2, it is reasonably selective for CB1, with a Ki of 0.7nM at CB1 and 8.6nM at CB2, a selectivity of around 12x. Resolution of the enantiomers of AM-4030 yields an even more potent compound, although with less selectivity, with the (−) enantiomer AM-4030a having a Ki of 0.6nM at CB1 and 1.1nM at CB2.
A cannabinoid receptor antagonist, also known simply as a cannabinoid antagonist or as an anticannabinoid, is a type of cannabinoidergic drug that binds to cannabinoid receptors (CBR) and prevents their activation by endocannabinoids. They include antagonists, inverse agonists, and antibodies of CBRs. The discovery of the endocannabinoid system led to the development of CB1 receptor antagonists. The first CBR inverse agonist, rimonabant, was described in 1994. Rimonabant blocks the CB1 receptor selectively and has been shown to decrease food intake and regulate body-weight gain. The prevalence of obesity worldwide is increasing dramatically and has a great impact on public health. The lack of efficient and well-tolerated drugs to cure obesity has led to an increased interest in research and development of CBR antagonists. Cannabidiol (CBD), a naturally occurring cannabinoid and a non-competitive CB1/CB2 receptor antagonist, as well as Δ9-tetrahydrocannabivarin (THCV), a naturally occurring cannabinoid, modulate the effects of THC via direct blockade of cannabinoid CB1 receptors, thus behaving like first-generation CB1 receptor inverse agonists, such as rimonabant. CBD is a very low-affinity CB1 ligand, that can nevertheless affect CB1 receptor activity in vivo in an indirect manner, while THCV is a high-affinity CB1 receptor ligand and potent antagonist in vitro and yet only occasionally produces effects in vivo resulting from CB1 receptor antagonism. THCV has also high affinity for CB2 receptors and signals as a partial agonist, differing from both CBD and rimonabant.
Abnormal cannabidiol (Abn-CBD) is a synthetic regioisomer of cannabidiol, which unlike most other cannabinoids produces vasodilator effects, lowers blood pressure, and induces cell migration, cell proliferation and mitogen-activated protein kinase activation in microglia, but without producing any psychoactive or sedative effects. Abn-CBD can be found as an impurity in synthetic cannabidiol.
AM-630 (6-Iodopravadoline) is a drug that acts as a potent and selective inverse agonist for the cannabinoid receptor CB2, with a Ki of 32.1 nM at CB2 and 165x selectivity over CB1, at which it acted as a weak partial agonist. It is used in the study of CB2 mediated responses and has been used to investigate the possible role of CB2 receptors in the brain. AM-630 is significant as one of the first indole derived cannabinoid ligands substituted on the 6-position of the indole ring, a position that has subsequently been found to be important in determining affinity and efficacy at both the CB1 and CB2 receptors, and has led to the development of many related derivatives.
AM-2233 is a drug that acts as a highly potent full agonist for the cannabinoid receptors, with a Ki of 1.8 nM at CB1 and 2.2 nM at CB2 as the active (R) enantiomer. It was developed as a selective radioligand for the cannabinoid receptors and has been used as its 131I derivative for mapping the distribution of the CB1 receptor in the brain. AM-2233 was found to fully substitute for THC in rats, with a potency lower than that of JWH-018 but higher than WIN 55,212-2.
KM-233 is a synthetic cannabinoid drug which is a structural analog of Δ8-tetrahydrocannabinol (THC), the less active but more stable isomer of the active component of Cannabis. KM-233 differs from Δ8-THC by the pentyl side chain being replaced by a 1,1-dimethylbenzyl group. It has high binding affinity in vitro for both the CB1 and CB2 receptors, with a CB2 affinity of 0.91 nM and 13-fold selectivity over the CB1 receptor. In animal studies, it has been found to be a potential treatment for glioma, a form of brain tumor. Many related analogues are known where the 1,1-dimethylbenzyl group is substituted or replaced by other groups, with a fairly well established structure-activity relationship.
Cannabidiol-dimethylheptyl (CBD-DMH or DMH-CBD) is a synthetic homologue of cannabidiol where the pentyl chain has been replaced by a dimethylheptyl chain. Several isomers of this compound are known. The most commonly used isomer in research is (−)-CBD-DMH, which has the same stereochemistry as natural cannabidiol, and a 1,1-dimethylheptyl side chain. This compound is not psychoactive and acts primarily as an anandamide reuptake inhibitor, but is more potent than cannabidiol as an anticonvulsant and has around the same potency as an antiinflammatory. Unexpectedly the “unnatural” enantiomer (+)-CBD-DMH, which has reversed stereochemistry from cannabidiol, was found to be a directly acting cannabinoid receptor agonist with a Ki of 17.4nM at CB1 and 211nM at CB2, and produces typical cannabinoid effects in animal studies, as does its 7-OH derivative.
11-Hydroxycannabinol (11-OH-CBN) is the main active metabolite of cannabinol (CBN), one of the active components of cannabis, and has also been isolated from cannabis itself. It is more potent than CBN itself, acting as an agonist of CB1 with around the same potency as THC, but is a weak antagonist at CB2.
ADB-BINACA (also known as ADMB-BZINACA using EMCDDA naming standards) is a cannabinoid designer drug that has been found as an ingredient in some synthetic cannabis products. It was originally developed by Pfizer as a potential analgesic, and is a potent agonist of the CB1 receptor with a binding affinity (Ki) of 0.33 nM and an EC50 of 14.7 nM.
AM-11245 is a drug which is a cannabinoid agonist from the classical cannabinoid family. It has high affinity and efficacy at both the CB1 and CB2 cannabinoid receptors, with a Ki of 0.4nM at both CB1 and CB2, and an EC50 of ~0.06nM at CB1 and 0.2nM at CB2, making it one of the most potent cannabinoid agonists identified to date.
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