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).
JWH-015 is a chemical from the naphthoylindole family that acts as a subtype-selective cannabinoid agonist. Its affinity for CB2 receptors is 13.8 nM, while its affinity for CB1 is 383 nM, meaning that it binds almost 28 times more strongly to CB2 than to CB1. However, it still displays some CB1 activity, and in some model systems can be very potent and efficacious at activating CB1 receptors, and therefore it is not as selective as newer drugs such as JWH-133. It has been shown to possess immunomodulatory effects, and CB2 agonists may be useful in the treatment of pain and inflammation. It was discovered and named after John W. Huffman.
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.
L-759,633 is an analgesic drug that is a cannabinoid agonist. It is a fairly selective agonist for the CB2 receptor, with selectivity of 163x for CB2 over CB1.
L-759,656 is an analgesic drug that is a cannabinoid agonist. It is a highly selective agonist for the CB2 receptor, with selectivity of 414x for CB2 over CB1, although it is still not as selective as newer agents such as HU-308.
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.
AM-1241 (1-(methylpiperidin-2-ylmethyl)-3-(2-iodo-5-nitrobenzoyl)indole) is a chemical from the aminoalkylindole family that acts as a potent and selective agonist for the cannabinoid receptor CB2, with a Ki of 3.4 nM at CB2 and 80 times selectivity over the related CB1 receptor. It has analgesic effects in animal studies, particularly against "atypical" pain such as hyperalgesia and allodynia. This is thought to be mediated through CB2-mediated peripheral release of endogenous opioid peptides, as well as direct activation of the TRPA1 channel. It has also shown efficacy in the treatment of amyotrophic lateral sclerosis in animal models.
A-834,735 is a drug developed by Abbott Laboratories that acts as a potent cannabinoid receptor full agonist at both the CB1 and CB2 receptors, with a Ki of 12 nM at CB1 and 0.21 nM at CB2. Replacing the aromatic 3-benzoyl or 3-naphthoyl group found in most indole derived cannabinoids with the 3-tetramethylcyclopropylmethanone group of A-834,735 and related compounds imparts significant selectivity for CB2, with most compounds from this group found to be highly selective CB2 agonists with little affinity for CB1. However, low nanomolar CB1 binding affinity is retained with certain heterocyclic 1-position substituents such as (N-methylpiperidin-2-yl)methyl (cf. AM-1220, AM-1248), or the (tetrahydropyran-4-yl)methyl substituent of A-834,735, resulting in compounds that still show significant affinity and efficacy at both receptors despite being CB2 selective overall.
AM-1221 is a drug that acts as a potent and selective agonist for the cannabinoid receptor CB2, with a Ki of 0.28 nM at CB2 and 52.3 nM at the CB1 receptor, giving it around 180 times selectivity for CB2. The 2-methyl and 6-nitro groups on the indole ring both tend to increase CB2 affinity while generally reducing affinity at CB1, explaining the high CB2 selectivity of AM-1221. However, despite this relatively high selectivity for CB2, its CB1 affinity is still too strong to make it useful as a truly selective CB2 agonist, so the related compound AM-1241 is generally preferred for research purposes.
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-679 (part of the AM cannabinoid series) is a drug that acts as a moderately potent agonist for the cannabinoid receptors, with a Ki of 13.5 nM at CB1 and 49.5 nM at CB2. AM-679 was one of the first 3-(2-iodobenzoyl)indole derivatives that was found to have significant cannabinoid receptor affinity, and while AM-679 itself has only modest affinity for these receptors, it was subsequently used as a base to develop several more specialised cannabinoid ligands that are now widely used in research, including the potent CB1 agonists AM-694 and AM-2233, and the selective CB2 agonist AM-1241. AM-679 was first identified as having been sold as a cannabinoid designer drug in Hungary in 2011, along with another novel compound 1-pentyl-3-(1-adamantoyl)indole.
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.
AM-1248 is a drug that acts as a moderately potent agonist for both the cannabinoid receptors CB1 and CB2, but with some dispute between sources over its exact potency and selectivity. Replacing the 3-(1-naphthoyl) group found in many indole derived cannabinoid ligands, with an adamantoyl group, generally confers significant CB2 selectivity, but reasonable CB1 affinity and selectivity is retained when an N-methylpiperidin-2-ylmethyl substitution is used at the indole 1-position. The related compound 1-pentyl-3-(1-adamantoyl)indole was identified as having been sold as a cannabinoid designer drug in Hungary in 2011, along with another synthetic cannabinoid AM-679.
AM-1235 (1-(5-fluoropentyl)-3-(naphthalen-1-oyl)-6-nitroindole) is a drug that acts as a potent and reasonably selective agonist for the cannabinoid receptor CB1.
AM-1220 is a drug that acts as a potent and moderately selective agonist for the cannabinoid receptor CB1, with around 19 times selectivity for CB1 over the related CB2 receptor. It was originally invented in the early 1990s by a team led by Thomas D'Ambra at Sterling Winthrop, but has subsequently been researched by many others, most notably the team led by Alexandros Makriyannis at the University of Connecticut. The (piperidin-2-yl)methyl side chain of AM-1220 contains a stereocenter, so there are two enantiomers with quite different potency, the (R)-enantiomer having a Ki of 0.27 nM at CB1 while the (S)-enantiomer has a much weaker Ki of 217 nM.
AB-001 (1-pentyl-3-(1-adamantoyl)indole) is a designer drug that was found as an ingredient in synthetic cannabis smoking blends in Ireland in 2010 and Hungary and Germany in 2011. It is unclear who AB-001 was originally developed by, but it is structurally related to compounds such as AM-1248 and its corresponding 1-(tetrahydropyran-4-ylmethyl) analogue, which are known to be potent cannabinoid agonists with moderate to a high selectivity for CB2 over CB1. The first published synthesis and pharmacological evaluation of AB-001 revealed that it acts as a full agonist at CB1 (EC50 = 35 nM) and CB2 receptors (EC50 = 48 nM). However, AB-001 was found to possess only weak cannabimimetic effects in rats at doses up to 30 mg/kg, making it less potent than the carboxamide analogue APICA, which possesses potent cannabimimetic activity at doses of 3 mg/kg.
MN-25 (UR-12) is a drug invented by Bristol-Myers Squibb, that acts as a reasonably selective agonist of peripheral cannabinoid receptors. It has moderate affinity for CB2 receptors with a Ki of 11 nM, but 22x lower affinity for the psychoactive CB1 receptors with a Ki of 245 nM. The indole 2-methyl derivative has the ratio of affinities reversed however, with a Ki of 8 nM at CB1 and 29 nM at CB2, which contrasts with the usual trend of 2-methyl derivatives having increased selectivity for CB2 (cf. JWH-018 vs JWH-007, JWH-081 vs JWH-098).
AM-2389 is a classical cannabinoid derivative which acts as a potent and reasonably selective agonist for the CB1 receptor, with a Ki of 0.16 nM, and 26× selectivity over the related CB2 receptor. It has high potency in animal tests of cannabinoid activity, and a medium duration of action. Replacing the 1',1'-dimethyl substitution of the dimethylheptyl side chain of classical cannabinoids with cyclopropyl or cyclopentyl results in higher potency than cyclobutyl, but only the cyclobutyl derivatives show selectivity for CB1 over CB2. High selectivity for CB1 over CB2 is difficult to achieve (cf. AM-906, AM-1235), as almost all commonly used CB1 agonists have similar or greater affinity for CB2 than CB1, and the only truly highly selective CB1 agonists known as of 2012 are eicosanoid derivatives such as O-1812.
AM-1714 (part of the AM cannabinoid series) is a drug that acts as a reasonably selective agonist of the peripheral cannabinoid receptor CB2, with sub-nanomolar affinity and 490x selectivity over the related CB1 receptor. In animal studies it has both analgesic and anti-allodynia effects. The 9-methoxy derivative AM-1710 has similar CB2 affinity but only 54x selectivity over CB1.
