Enantioselective synthesis of 1-methoxy- and 1-deoxy-2'-methyl-delta8-tetrahydrocannabinols: new selective ligands for the CB2 receptor

Two new series of cannabinoids were prepared and their affinities for the CB1 and CB2 receptors were determined. These series are the (2'R)- and (2'S)-1-methoxy- and 1-deoxy-3-(2'-methylalkyl)-delta8-tetrahydrocannabinols, with alkyl side chains of three to seven carbon atoms. These compounds were prepared by a route that employed the enantioselective synthesis of the resorcinol precursors to the cannabinoid ring system. All of these compounds have greater affinity for the CB2 receptor than the CB1 receptor and four of them, (2'R)-1-methoxy-3-(2'-methylbutyl)-delta8-THC (JWH-359), (2'S)-1-deoxy-3-(2'-methylbutyl)-delta8-THC (JWH-352), (2'S)-1-deoxy-3-(2'-methylpentyl)-delta8-THC (JWH-255), and (2'R)-1-deoxy-3-(2'-methylpentyl)-delta8-THC (JWH-255), have good affinity (K(i) = 13-47 nM) for the CB2 receptor and little affinity (K(i) = 1493 to >10,000 nM) for the CB1 receptor. In the 1-deoxy-3-(2'-methylalkyl)-delta8-THC series, the 2'S-methyl compounds in general have greater affinity for the CB2 receptor than the corresponding 2'R isomers.     

1-Methoxy-, 1-deoxy-11-hydroxy- and 11-hydroxy-1-methoxy-Delta(8)-tetrahydrocannabinols: new selective ligands for the CB2 receptor

Three series of new cannabinoids were prepared and their affinities for the CB₁ and CB₂ cannabinoid recptors were determined. These are the 1-methoxy-3-(1′,1′-dimethylalkyl)-, 1-deoxy-11-hydroxy-3-(1′,1′-dimethylalkyl)- and 11-hydroxy-1-methoxy-3-(1′,1′-dimethylalkyl)-Δ⁸-tetrahydrocannabinols, which contain alkyl chains from dimethylethyl to dimethylheptyl appended to C-3 of the cannabinoid. All of these compounds have greater affinity for the CB₂ receptor than for the CB₁ receptor, however only 1-methoxy-3-(1′,1′-dimethylhexyl)-Δ⁸-THC (JWH-229, 6e) has effectively no affinity for the CB₁ receptor (K_i=3134±110 nM) and high affinity for CB₂ (K_i=18±2 nM).     

Structure-activity relationships for 1',1'-dimethylalkyl-Delta8-tetrahydrocannabinols

A series of 1',1'-dimethylalkyl-Delta(8)-tetrahydrocannabinol analogues with C-3 side chains of 2-12 carbon atoms has been synthesized and their in vitro and in vivo pharmacology has been evaluated. The lowest member of the series, 1',1'-dimethylethyl-Delta(8)-THC (8, n=0) has good affinity for the CB(1) receptor, but is inactive in vivo. The dimethylpropyl (8, n=1) through dimethyldecyl (8, n=8) all have high affinity for the CB(1) receptor and are full agonists in vivo. 1',1'-Dimethylundecyl-Delta(8)-THC (8, n=9) has significant affinity for the receptor (K(i)=25.8+/-5.8 nM), but has reduced potency in vivo. The dodecyl analogue (8, n=10) has little affinity for the CB(1) receptor and is inactive in vivo. A quantitative structure-activity relationship study of the side chain region of these compounds is consistent with the concept that for optimum affinity and potency the side chain must be of a length which will permit its terminus to loop back in proximity to the phenolic ring of the cannabinoid.     

3-(1',1'-Dimethylbutyl)-1-deoxy-delta8-THC and related compounds: synthesis of selective ligands for the CB2 receptor

The synthesis and pharmacology of 15 1-deoxy-delta8-THC analogues, several of which have high affinity for the CB2 receptor, are described. The deoxy cannabinoids include 1-deoxy-11-hydroxy-delta8-THC (5), 1-deoxy-delta8-THC (6), 1-deoxy-3-butyl-delta8-THC (7), 1-deoxy-3-hexyl-delta8-THC (8) and a series of 3-(1',1'-dimethylalkyl)-1-deoxy-delta8-THC analogues (2, n = 0-4, 6, 7, where n = the number of carbon atoms in the side chain-2). Three derivatives (17-19) of deoxynabilone (16) were also prepared. The affinities of each compound for the CB1 and CB2 receptors were determined employing previously described procedures. Five of the 3-(1',1'-dimethylalkyl)-1-deoxy-delta8-THC analogues (2, n = 1-5) have high affinity (Ki = < 20 nM) for the CB2 receptor. Four of them (2, n = 1-4) also have little affinity for the CB1 receptor (Ki = > 295 nM). 3-(1',1'-Dimethylbutyl)-1-deoxy-delta8-THC (2, n = 2) has very high affinity for the CB2 receptor (Ki = 3.4 +/- 1.0 nM) and little affinity for the CB1 receptor (Ki = 677 +/- 132 nM).     

3-Indolyl-1-naphthylmethanes: new cannabimimetic indoles provide evidence for aromatic stacking interactions with the CB(1) cannabinoid receptor

A series of 1-pentyl-1H-indol-3-yl-(1-naphthyl)methanes (9-11) and 2-methyl-1-pentyl-1H-indol-3-yl-(1-naphthyl)methanes (12-14) have been synthesized to investigate the hypothesis that cannabimimetic 3-(1-naphthoyl)indoles interact with the CB(1) receptor by hydrogen bonding to the carbonyl group. Indoles 9-11 have significant (K(i)=17-23nM) receptor affinity, somewhat less than that of the corresponding naphthoylindoles (5, 15, 16). 2-Methyl-1-indoles 12-14 have little affinity for the CB(1) receptor, in contrast to 2-methyl-3-(1-naphthoyl)indoles 17-19, which have affinities comparable to those of 5, 15, 16. A cannabimimetic indene hydrocarbon (26) was synthesized and found to have K(i)=26+/-4nM. Molecular modeling and receptor docking studies of naphthoylindole 16, its 2-methyl congener (19) and indolyl-1-naphthylmethanes 11 and 14, combined with the receptor affinities of these cannabimimetic indoles, strongly suggest that these cannabinoid receptor ligands bind primarily by aromatic stacking interactions in the transmembrane helix 3-4-5-6 region of the CB(1) receptor.     

Phase I hydroxylated metabolites of the K2 synthetic cannabinoid JWH-018 retain in vitro and in vivo cannabinoid 1 receptor affinity and activity

Background

K2 products are synthetic cannabinoid-laced, marijuana-like drugs of abuse, use of which is often associated with clinical symptoms atypical of marijuana use, including hypertension, agitation, hallucinations, psychosis, seizures and panic attacks. JWH-018, a prevalent K2 synthetic cannabinoid, is structurally distinct from Δ⁹-THC, the main psychoactive ingredient in marijuana. Since even subtle structural differences can lead to differential metabolism, formation of novel, biologically active metabolites may be responsible for the distinct effects associated with K2 use. The present study proposes that K2''s high adverse effect occurrence is due, at least in part, to distinct JWH-018 metabolite activity at the cannabinoid 1 receptor (CB1R).

Methods/Principal Findings

JWH-018, five potential monohydroxylated metabolites (M1–M5), and one carboxy metabolite (M6) were examined in mouse brain homogenates containing CB1Rs, first for CB1R affinity using a competition binding assay employing the cannabinoid receptor radioligand [³H]CP-55,940, and then for CB1R intrinsic efficacy using an [³⁵S]GTPγS binding assay. JWH-018 and M1–M5 bound CB1Rs with high affinity, exhibiting K_i values that were lower than or equivalent to Δ⁹-THC. These molecules also stimulated G-proteins with equal or greater efficacy relative to Δ⁹-THC, a CB1R partial agonist. Most importantly, JWH-018, M2, M3, and M5 produced full CB1R agonist levels of activation. CB1R-mediated activation was demonstrated by blockade with O-2050, a CB1R-selective neutral antagonist. Similar to Δ⁹-THC, JWH-018 and M1 produced a marked depression of locomotor activity and core body temperature in mice that were both blocked by the CB1R-preferring antagonist/inverse agonist AM251.

Conclusions/Significance

Unlike metabolites of most drugs, the studied JWH-018 monohydroxylated compounds, but not the carboxy metabolite, retain in vitro and in vivo activity at CB1Rs. These observations, combined with higher CB1R affinity and activity relative to Δ⁹-THC, may contribute to the greater prevalence of adverse effects observed with JWH-018-containing products relative to cannabis.     

Synthesis and pharmacology of 1-alkyl-3-(1-naphthoyl)indoles: steric and electronic effects of 4- and 8-halogenated naphthoyl substituents

To develop SAR at both the cannabinoid CB(1) and CB(2) receptors for 3-(1-naphthoyl)indoles bearing moderately electron withdrawing substituents at C-4 of the naphthoyl moiety, 1-propyl and 1-pentyl-3-(4-fluoro, chloro, bromo and iodo-1-naphthoyl) derivatives were prepared. To study the steric and electronic effects of substituents at the 8-position of the naphthoyl group, the 3-(4-chloro, bromo and iodo-1-naphthoyl)indoles were also synthesized. The affinities of both groups of compounds for the CB(1) and CB(2) receptors were determined and several of them were evaluated in vivo in the mouse. The effects of these substituents on receptor affinities and in vivo activity are discussed and structure-activity relationships are presented. Although many of these compounds are selective for the CB(2) receptor, only three JWH-423, 1-propyl-3-(4-iodo-1-naphthoyl)indole, JWH-422, 2-methyl-1-propyl-3-(4-iodo-1-naphthoyl)indole, the 2-methyl analog of JWH-423 and JWH-417, 1-pentyl-3-(8-iodo-1-naphthoyl)indole, possess the desirable combination of low CB(1) affinity and good CB(2) affinity.     

Novel sterically hindered cannabinoid CB1 receptor ligands

In the present study, 11 novel N-(3,3-diphenyl)propyl-2,2-diphenylacetamide derivatives (4a-d and 9a-g) and six triphenylacetamides (10a-c and 11a-c) were synthesized and tested as ligands of cannabinoid CB(1) and CB(2) receptors. All compounds exhibited affinity for CB(1) and CB(2) receptors. Four compounds (4b, 9a, 9b, and 11a) showed selectivity for CB(1) versus CB(2) receptors, although only the N-(3,3-diphenyl)propyl-2,2-diphenylacetamide (4b) can be considered a potent CB(1) ligand (K(i)=58 nM). It was 140-fold selective over CB(2) receptors (K(i)=7800 nM) and behaved as an inverse agonist by stimulating forskolin-induced cAMP formation in mouse N18TG2 neuroblastoma cells. This compound is the first of a novel class of tetraphenyl CB(1) ligands that, in view of its easy synthesis and high affinity for CB(1) receptors and despite its sterical hindrance, will be useful for the design of new blockers of this therapeutically exploitable receptor type.     

1-Pentyl-3-phenylacetylindoles, a new class of cannabimimetic indoles

A new class of cannabimimetic indoles, with 3-phenylacetyl or substituted 3-phenylacetyl substituents, has been prepared and their affinities for the cannabinoid CB1 and CB2 receptors have been determined. In general those compounds with a 2-substituted phenylacetyl group have good affinity for both receptors. The 4-substituted analogs have little affinity for either receptor, while the 3-substituted compounds are intermediate in their affinities. Two of these compounds, 1-pentyl-3-(2-methylphenylacetyl)indole (JWH-251) and 1-pentyl-3-(3-methoxyphenylacetyl)indole (JWH-302), have 5-fold selectivity for the CB1 receptor with modest affinity for the CB2 receptor. GTPgammaS determinations indicate that both compounds are highly efficacious agonists at the CB1 receptor and partial agonists at the CB2 receptor.     

1-Methoxy-, 1-deoxy-11-hydroxy- and 11-Hydroxy-1-methoxy-Δ-tetrahydrocannabinols: new selective ligands for the CB2 receptor

Three series of new cannabinoids were prepared and their affinities for the CB₁ and CB₂ cannabinoid recptors were determined. These are the 1-methoxy-3-(1′,1′-dimethylalkyl)-, 1-deoxy-11-hydroxy-3-(1′,1′-dimethylalkyl)- and 11-hydroxy-1-methoxy-3-(1′,1′-dimethylalkyl)-Δ⁸-tetrahydrocannabinols, which contain alkyl chains from dimethylethyl to dimethylheptyl appended to C-3 of the cannabinoid. All of these compounds have greater affinity for the CB₂ receptor than for the CB₁ receptor, however only 1-methoxy-3-(1′,1′-dimethylhexyl)-Δ⁸-THC (JWH-229, 6e) has effectively no affinity for the CB₁ receptor (K_i=3134±110 nM) and high affinity for CB₂ (K_i=18±2 nM).     

1-Alkyl-2-aryl-4-(1-naphthoyl)pyrroles: new high affinity ligands for the cannabinoid CB1 and CB2 receptors

Two series of 1-alkyl-2-aryl-4-(1-naphthoyl)pyrroles were synthesized and their affinities for the cannabinoid CB(1) and CB(2) receptors were determined. In the 2-phenyl series (5) the N-alkyl group was varied from n-propyl to n-heptyl. A second series of 23 1-pentyl-2-aryl-4-(1-naphthoyl)-pyrroles (6) was also prepared. Several compounds in both series have CB(1) receptor affinities in the 6-30nM range. The high affinities of these pyrrole derivatives relative to JWH-030 (1, R=C(5)H(11)) support the hypothesis that these pyrroles interact with the CB(1) receptor primarily by aromatic stacking.     

Synthesis and pharmacology of 1-deoxy analogs of CP-47,497 and CP-55,940

A series of 1-deoxy analogs of CP-47,497 (8 and 13, n=0-7) and 1-deoxy analogs of CP-55,940 (9, n=0-7) have been synthesized and their affinities for the cannabinoid CB(1) and CB(2) receptors have been determined. Although the majority of these compounds exhibit selectivity for the CB(2) receptor, none have greater than modest affinity for either receptor. The interactions of these 1-deoxy nontraditional cannabinoids with the CB(2) receptor are discussed.     

Stereochemical selectivity of methanandamides for the CB1 and CB2 cannabinoid receptors and their metabolic stability.

Several chiral, analogues of the endogenous cannabinoid receptor ligand, arachidonylethanolamide (anandamide), methylated at the 2,1' and 2' positions using asymmetric synthesis were evaluated in order to study (a) stereoselectivity of binding to CB1 and CB2 cannabinoid receptors; and (b) metabolic stability with regard to anandamide amidase. Enantiomerically pure 2-methyl arachidonic acids were synthesized through diastereoselective methylation of the respective chiral 2-oxazolidinone enolate derivatives and CB1 and CB2 receptor affinities of the resulting chiral anandamides were evaluated using a standard receptor binding assay. Introduction of a single 2-methyl group increased affinity for CB1, led to limited enantioselectivity and only modestly improved metabolic stability. However, a high degree of enantio- and diastereoselectivity was observed for the 2,1'-dimethyl analogues. (R)-N-(1-methyl-2-hydroxyethyl)-2-(R)-methyl-arachidonamide (4) exhibited the highest CB1 receptor affinity in this series with a K(i) of 7.42 nM, an at least 10-fold improvement on anandamide (K(i)=78.2 nM). The introduction of two methyl groups at the 2-position of anandamide led to no change in affinity for CB1 but somewhat enhanced metabolic stability. Conversely, chiral headgroup methylation in the 2-gem-dimethyl series led to chiral analogues possessing a wide range of CB1 affinities. Of these the (S)-2,2,2'-trimethyl analogue (12) had the highest affinity for CB1 almost equal to that of anandamide. In agreement with our previous anandamide structure-activity relationship work, the analogues in this study showed high selectivity for the CB1 receptor over CB2. The results are evaluated in terms of stereochemical factors affecting the ligand's affinity for CB1 using receptor-essential volume mapping as an aid. Based on the results, a partial CB1 receptor site model is proposed, that bears two hydrophobic pockets capable of accommodating 1'- and 2-methyl groups     

Synthesis and biological evaluation of 1,8-naphthyridin-4(1H)-on-3-carboxamide derivatives as new ligands of cannabinoid receptors

Cannabinoid receptors have been studied extensively in view of their potential functional role in several physiological and pathological processes. For this reason, the search for new potent, selective ligands for subtype CB receptors, CB(1) and CB(2), is still of great importance, in order to investigate their role in various physiological functions. The present study describes the synthesis and the biological properties of a series of 1,8-naphthyridine derivatives, characterised by the presence of some important structural requirements exhibited by other classes of cannabinoid ligands, such as an aliphatic or aromatic carboxamide group in position 3, and an alkyl or arylalkyl substituent in position 1. These compounds were assayed for binding both to the brain and to peripheral cannabinoid receptors (CB(1) and CB(2)). The results obtained indicate that the naphthyridine derivatives examined possess a greater affinity for the CB(2) receptor than for the CB(1) receptor. In particular, derivatives 6a and 7a possess an appreciable affinity for the CB(2) receptor, with K(i) values of 5.5 and 8.0 nM respectively; also compounds 4a, 5a and 8a exhibit a good CB(2) affinity, with K(i) values in the range of 10-44 nM. Furthermore, compounds 3g-i and 18 revealed a good CB(2) selectivity, with a CB(1)/CB(2) ratio >20.     

A pyridone analogue of traditional cannabinoids. A new class of selective ligands for the CB(2) receptor

A pyridone analogue (5) of the potent bicyclic cannabinoid CP 47,497 (6) has been synthesized as a model for one conformational isomer of anandamide and to test the hypothesis that an amide carbonyl may serve as a hydrogen bond acceptor in interactions with the CB(1) cannabinoid receptor. Pyridone 5 was synthesized from 6-bromo-2-methoxypyridine (10) by palladium catalyzed coupling with 1-pentyne to provide 11. Catalytic hydrogenation of 11 and hydrolysis to pyridone 13 followed by N-alkylation gave 1-propyl-6-pentyl-2-pyridone (15). Bromination of 15 gave dibromide 18, which underwent Heck coupling with cyclohex-2-en-1-one to give enone 19. Catalytic hydrogenation of 19 gave ketone 20 which was reduced using NaBH(4) to alcohol 5. Reduction of 20 with K-Selectride gave the axial epimer of 5 (21). Neither alcohol 5 nor 21 have significant affinity for the CB(1) receptor (K(i) > 970 nM), but both have moderately high affinity for the CB(2) receptor (K(i) < 60 nM).     

Synthesis and structure-activity relationships of a series of pyrrole cannabinoid receptor agonists

We designed and synthesized a series of pyrrole derivatives with the aim of investigating the structure-activity relationship (SAR) for the binding of non-classical agonists to CB(1) and CB(2) cannabinoid receptors. Superposition of two pyrrole-containing cannabinoid agonists, JWH-007 and JWH-161, allowed us to identify positions 1, 3 and 4 of the pyrrole nucleus as amenable to additional investigation. We prepared the 1-alkyl-2,5-dimethyl-3,4-substituted pyrroles 10a-e, 11a-d, 17, 21, 25 and the tetrahydroindole 15, and evaluated their ability to bind to and activate cannabinoid receptors. Noteworthy in this set of compounds are the 4-bromopyrrole 11a, which has an affinity for CB(1) and CB(2) receptors comparable to that of well-characterized heterocyclic cannabimimetics such as Win-55,212-2; the amide 25, which, although possessing a moderate affinity for cannabinoid receptors, demonstrates that the 3-naphthoyl group, commonly present in indole and pyrrole cannabimimetics, can be substituted by alternative moieties; and compounds 10d, 11d, showing CB(1) partial agonist properties.     

Tricyclic pyrazoles. Part 1: synthesis and biological evaluation of novel 1,4-dihydroindeno[1,2-c]pyrazol-based ligands for CB1and CB2 cannabinoid receptors

Cannabinoids receptors, cellular elements of the endocannabinoid system, have been the focus of extensive studies because of their potential functional role in several important physiological and pathological processes. To further evaluate the properties of CB receptors, especially CB(1) and CB(2) subtypes, we have designed, using SR141716A as a benchmark, a new series of rigid 1-aryl-1,4-dihydroindeno[1,2-c]pyrazole-3-carboxamides. Compounds 1 were synthesized from substituted 1-aryl-1,4-dihydroindeno[1,2-c]pyrazole-3-carboxylic acids and requisite amines. The various analogues were assayed for binding both to the brain and peripheral cannabinoid receptors (CB(1) and CB(2)). Seven of the new compounds displayed very high in vitro CB(2) binding affinities, especially 1a, 1b, 1c, 1e, 1g, 1h and 1j which showed K(i) values of 0.34, 0.225, 0.27, 0.23, 0.385, 0.037 and 0.9 nM, respectively. Compounds 1a, 1b, 1c and 1h showed the highest selectivity for CB(2) receptor with K(i)(CB(1)) to K(i)(CB(2)) ratios of 6029, 5635, 5814 and 9810, respectively. Noticeably, 1h exhibited the highest affinity and selectivity for CB(2) receptors.     

Structure-activity relationships for 1-alkyl-3-(1-naphthoyl)indoles at the cannabinoid CB(1) and CB(2) receptors: steric and electronic effects of naphthoyl substituents. New highly selective CB(2) receptor agonists

In an effort to improve indole-based CB(2) cannabinoid receptor ligands and also to develop SAR for both the CB(1) and CB(2) receptors, 47 indole derivatives were prepared and their CB(1) and CB(2) receptor affinities were determined. The indole derivatives include 1-propyl- and 1-pentyl-3-(1-naphthoyl)indoles both with and without a 2-methyl substituent. Naphthoyl substituents include 4- and 7-alkyl groups as well as 2-, 4-, 6-, 7-methoxy and 4-ethoxy groups. The effects of these substituents on receptor affinities are discussed and structure-activity relationships are presented. In the course of this work three new highly selective CB(2) receptor agonists were identified, 1-propyl-3-(4-methyl-1-naphthoylindole (JWH-120), 1-propyl-2-methyl-3-(6-methoxy-1-naphthoylindole (JWH-151), and 1-pentyl-3-(2-methoxy-1-naphthoylindole (JWH-267). GTPgammaS assays indicated that JWH-151 is a full agonist at CB(2), while JWH-120 and JWH-267 are partial agonists. Molecular modeling and receptor docking studies were carried out on a set of 3-(4-propyl-1-naphthoyl)indoles, a set of 3-(6-methoxy-1-naphthoyl)indoles and the pair of N-pentyl-3-(2-methoxy-1-naphthoyl)indoles. Docking studies indicated that the CB(1) receptor affinities of these compounds were consistent with their aromatic stacking interactions in the aromatic microdomain of the CB(1) receptor.     

Structural modifications of the cannabinoid side chain towards C3-aryl and 1',1'-cycloalkyl-1'-cyano cannabinoids

The compounds reported in this study are Delta(8)-THC analogues in which the C3 five-carbon linear side chain of Delta(8)-THC was replaced with aryl and 1',1'-cycloalkyl substituents. Of the compounds described here analogues 2d (CB(1), K(i)=11.7 nM. CB(2), K(i)=9.39 nM) and 2f (CB(1), K(i)=8.26 nM. CB(2), K(i)=3.86 nM) exhibited enhanced binding affinities for CB(1) and CB(2), exceeding that of Delta(8)-THC. Efficient procedures for the synthesis of these novel cannabinoid analogues are described.     

Synthesis and structure-activity relationships (SARs) of 1,5-diarylpyrazole cannabinoid type-1 (CB(1)) receptor ligands for potential use in molecular imaging

Cannabinoid type-1 (CB(1)) receptor ligands, derived from the 1,5-diarylpyrazole core template of rimonabant (Acomplia), have been the focus of several studies aimed at examining structure-activity relationships (SARs). The purpose of this study was to design and synthesize a set of compounds based on the 1,5-diarylpyrazole template while focusing on the potential for discovery of CB(1) receptor radioligands that might be used as probes with in vivo molecular imaging. Each synthesized ligand was evaluated for potency as an antagonist at CB(1) and cannabinoid type-2 (CB(2)) receptors in vitro using a GTPgamma(35)S-binding assay. clog P values were calculated with Pallas 3.0. The antagonist binding affinities (K(B)) at CB(1) receptors ranged from 11 to >16,000 nM, CB(1) versus CB(2) selectivities from 0.6 to 773, and clog Ps from 3.61 to 6.25. An interesting new ligand, namely N-(piperidin-1-yl)-1-(2-bromophenyl)-5-(4-methoxyphenyl)-4-methyl-1H-pyrazole-3-carboxamide (9j), emerged from the synthesized set with appealing properties (K(B)=11 nM; CB(1) selectivity>773; clog P=5.85), for labeling with carbon-11 and development as a radioligand for imaging brain CB(1) receptors in vivo with positron emission tomography (PET).