Cannabimimetic activity (delta 1-THC cue) of cannabidiol monomethyl ether and two stereoisomeric hexahydrocannabinols in rats and pigeons

An emerging trend in Novel Psychoactive Substances (NPSs): designer THC

Since its discovery as one of the main components of cannabis and its affinity towards the cannabinoid receptor CB1, serving as a means to exert its psychoactivity, Δ9-tetrahydrocannabinol (Δ9-THC) has inspired medicinal chemists throughout history to create more potent derivatives. Initially, the goal was to synthesize chemical probes for investigating the molecular mechanisms behind the pharmacology of Δ9-THC and finding potential medical applications. The unintended consequence of this noble intent has been the proliferation of these compounds for recreational use. This review comprehensively covers the most exhaustive number of THC-like cannabinoids circulating on the recreational market. It provides information on the chemistry, synthesis, pharmacology, analytical assessment, and experiences related to the psychoactive effects reported by recreational users on online forums. Some of these compounds can be found in natural cannabis, albeit in trace amounts, while others are entirely artificial. Moreover, to circumvent legal issues, many manufacturers resort to semi-synthetic processes starting from legal products extracted from hemp, such as cannabidiol (CBD). Despite the aim to encompass all known THC-like molecules, new species emerge on the drug users' pipeline each month. Beyond posing a significantly high public health risk due to unpredictable and unknown side effects, scientific research consistently lags behind the rapidly evolving recreational market.

Hexahydrocannabinol poisoning reported to French poison centres

INTRODUCTION

Hexahydrocannabinol is a hexahydro derivative of cannabinol. Poisoning with hexahydrocannabinol was first observed in Europe in May 2022.

METHOD

This is a retrospective observational study of cases of self-reported hexahydrocannabinol exposure reported to French poison centres between 1 January 2022 and 31 May 2023.

RESULTS

There were 37 cases, including 19 in May 2023. The median age of the patients was 36 (interquartile range 28-43) years, and most were men. Eight patients had a history of substance use disorder. The route of exposure was ingestion in 24, inhalation (smoking or vaping) in 10, inhalation and ingestion in two and sublingual in one. Clinical features were neurological (85 per cent), cardiovascular (61 per cent), gastrointestinal (33 per cent), psychiatric (27 per cent) and ocular (21 per cent). Fifty-nine per cent of the patients were hospitalized. In four patients, the Poisoning Severity Score was 0 (asymptomatic); in 15 patients, the Score was 1 (minor); in 16, the Score was 2 (moderate); and in two cases, the Score was 3 (severe). In 70 per cent of patients, the outcome was known, and all recovered. Testing of biological samples was only undertaken in six cases. Five patients had positive blood or urine tests for hexahydrocannabinol; in two patients, tetrahydrocannabinol and metabolites were also detected. In addition, there was an additional patient in whom Δ8- and Δ9-tetrahydrocannabinol was detected in the substances used.

DISCUSSION

Clinical effects reported in this series included neuropsychiatric and somatic effects. Whilst these cases related to self-reported hexahydrocannabinol use, it is likely that tetrahydrocannabinol use also contributed to the effects in a substantial proportion of cases. This study has some limitations, such as the lack of available information due to the retrospective nature of the study. As a result, it probably overestimates the number of moderate and severe cases due to under-reporting of cases of little or no severity. Analysis of the patient's blood and urine was performed only in six patients, so we cannot be certain that the products consumed by the other patients were hexahydrocannabinol.

CONCLUSION

The clinical effects attributed to hexahydrocannabinol were neurological, cardiovascular, gastrointestinal, psychiatric and ocular predominantly and were sometimes serious.

Conversion of Cannabidiol (CBD) into Psychotropic Cannabinoids Including Tetrahydrocannabinol (THC): A Controversy in the Scientific Literature

Cannabidiol (CBD) is a naturally occurring, non-psychotropic cannabinoid of the hemp plant Cannabis sativa L. and has been known to induce several physiological and pharmacological effects. While CBD is approved as a medicinal product subject to prescription, it is also widely sold over the counter (OTC) in the form of food supplements, cosmetics and electronic cigarette liquids. However, regulatory difficulties arise from its origin being a narcotic plant or its status as an unapproved novel food ingredient. Regarding the consumer safety of these OTC products, the question whether or not CBD might be degraded into psychotropic cannabinoids, most prominently tetrahydrocannabinol (THC), under in vivo conditions initiated an ongoing scientific debate. This feature review aims to summarize the current knowledge of CBD degradation processes, specifically the results of in vitro and in vivo studies. Additionally, the literature on psychotropic effects of cannabinoids was carefully studied with a focus on the degradants and metabolites of CBD, but data were found to be sparse. While the literature is contradictory, most studies suggest that CBD is not converted to psychotropic THC under in vivo conditions. Nevertheless, it is certain that CBD degrades to psychotropic products in acidic environments. Hence, the storage stability of commercial formulations requires more attention in the future.

Enantioselective Total Synthesis of Potent 9β-11-Hydroxyhexahydrocannabinol

The first total synthesis of potent cannabinoid, 9β-11-hydroxyhexahydrocannabinol, is achieved through a proline-catalyzed inverse-electron-demand Diels-Alder reaction. Using this asymmetric catalysis, the cyclohexane ring is constructed with two chiral centers as a single diastereomer with 97% ee. The creation of the third chiral center and benzopyran ring is demonstrated with the elegant synthetic strategies. This mild and efficient synthetic methodology provides a new route for the asymmetric synthesis of the other potent hexahydrocannabinols.

Preclinical studies on the reinforcing effects of cannabinoids. A tribute to the scientific research of Dr. Steve Goldberg

RATIONALE

The reinforcing effects of most abused drugs have been consistently demonstrated and studied in animal models, although those of marijuana were not, until the demonstration 15 years ago that delta-9-tetrahydrocannabinol (THC) could serve as a reinforcer in self-administration (SA) procedures in squirrel monkeys. Until then, those effects were inferred using indirect assessments.

OBJECTIVES

The aim of this manuscript is to review the primary preclinical procedures used to indirectly and directly infer reinforcing effects of cannabinoid drugs.

METHODS

Results will be reviewed from studies of cannabinoid discrimination, intracranial self-stimulation (ICSS), conditioned place preference (CPP), as well as change in levels of dopamine assessed in brain areas related to reinforcement, and finally from self-administration procedures. For each procedure, an evaluation will be made of the predictive validity in detecting the potential abuse liability of cannabinoids based on seminal papers, with the addition of selected reports from more recent years especially those from Dr. Goldberg's research group.

RESULTS AND CONCLUSIONS

ICSS and CPP do not provide consistent results for the assessment of potential for abuse of cannabinoids. However, drug discrimination and neurochemistry procedures appear to detect potential for abuse of cannabinoids, as well as several novel "designer cannabinoid drugs." Though after 15 years transfer of the self-administration model of marijuana abuse from squirrel monkeys to other species remains somewhat problematic, studies with the former species have substantially advanced the field, and several reports have been published with consistent self-administration of cannabinoid agonists in rodents.

Cannabinoid withdrawal in mice: inverse agonist vs neutral antagonist

RATIONALE

Previous reports shows rimonabant's inverse properties may be a limiting factor for treating cannabinoid dependence. To overcome this limitation, neutral antagonists were developed, to address mechanisms by which an inverse agonist and neutral antagonist elicit withdrawal.

OBJECTIVE

The objective of this study is to introduce an animal model to study cannabinoid dependence by incorporating traditional methodologies and profiling novel cannabinoid ligands with distinct pharmacological properties/modes of action by evaluating their pharmacological effects on CB1-receptor (CB1R) related physiological/behavioral endpoints.

METHODS

The cannabinergic AM2389 was acutely characterized in the tetrad (locomotor activity, analgesia, inverted screen/catalepsy bar test, and temperature), with some comparisons made to Δ(9)-tetrahydrocannabinol (THC). Tolerance was measured in mice repeatedly administered AM2389. Antagonist-precipitated withdrawal was characterized in cannabinoid-adapted mice induced by either centrally acting antagonists, rimonabant and AM4113, or an antagonist with limited brain penetration, AM6545.

RESULTS

In the tetrad, AM2389 was more potent and longer acting than THC, suggesting a novel approach for inducing dependence. Repeated administration of AM2389 led to tolerance by attenuating hypothermia that was induced by acute AM2389 administration. Antagonist-precipitated withdrawal signs were induced by rimonabant or AM4113, but not by AM6545. Antagonist-precipitated withdrawal was reversed by reinstating AM2389 or THC.

CONCLUSIONS

These findings suggest cannabinoid-precipitated withdrawal may not be ascribed to the inverse properties of rimonabant, but rather to rapid competition with the agonist at the CB1R. This withdrawal syndrome is likely centrally mediated, since only the centrally acting CB1R antagonists elicited withdrawal, i.e., such responses were absent after the purported peripherally selective CB1R antagonist AM6545.

"Herbal incense": designer drug blends as cannabimimetics and their assessment by drug discrimination and other in vivo bioassays

Recently, synthetic cannabinoids originally designed for testing in the laboratory only have found use recreationally in designer herbal blends, originally called "Spice". The myriad of compounds found are for the most part potent full agonists of the cannabinoid receptor 1, producing effects similar to tetrahydrocannabinol (THC) and marijuana. Drug discrimination of these compounds offers a specific behavioral test that can help determine whether these new synthetic compounds share a similar "subjective high" with the effects of marijuana/THC. By utilization of drug discrimination and other behavioral techniques, a better understanding of these new "designer" cannabinoids may be reached to assist in treating both the acute and chronic effects of these drugs. The paper provides a brief exposé of modern cannabinoid research as a backdrop to the recreational use of designer herbal blend cannabimimetics.

AM2389, a high-affinity, in vivo potent CB1-receptor-selective cannabinergic ligand as evidenced by drug discrimination in rats and hypothermia testing in mice

RATIONALE

The endocannabinoid signaling system (ECS) has been targeted for developing novel therapeutics since ECS dysfunction has been implicated in various pathologies. Current focus is on chemical modifications of the hexahydrocannabinol (HHC) nabilone (Cesamet(®)).

OBJECTIVE

To characterize the novel, high-affinity cannabinoid receptor 1 (CB(1)R) HHC-ligand AM2389 [9β-hydroxy-3-(1-hexyl-cyclobut-1-yl)-hexahydrocannabinol in two rodent pre-clinical assays.

MATERIALS AND METHODS

CB(1)R mediation of AM2389-induced hypothermia in mice was evaluated with AM251, a CB(1)R-selective antagonist/inverse agonist. Additionally, two groups of rats discriminated the full cannabinergic aminoalkylindole AM5983 (0.18 and 0.56 mg/kg) from vehicle 20 min post-injection in a two-choice operant conditioning task motivated by 0.1% saccharin/water. Generalization/substitution tests were conducted with AM2389, AM5983, and Δ(9)-tetrahydrocannabinol (Δ(9)-THC).

RESULTS

Δ(9)-THC (30 mg/kg)-induced hypothermia exhibited a faster onset and shorter duration of action compared with AM2389 (0.1 and 0.3 mg/kg). AM251 (3 and 10 mg/kg) attenuated/blocked hypothermia induced by 0.3 mg/kg AM2389. In drug discrimination, the order of potency was AM2389 > AM5983 > Δ(9)-THC with ED(50) values of 0.0025, 0.0571, and 0.2635 mg/kg, respectively, in the low-dose condition. The corresponding ED(50) values in the high-dose condition were 0.0069, 0.1246, and 0.8438 mg/kg, respectively. Onset of the effects of AM2389 was slow with a protracted time-course; the functional, perceptual in vivo half-life was approximately 17 h.

CONCLUSIONS

This potent cannabinergic HHC exhibited a slow onset of action with a protracted time-course. The AM2389 chemotype appears well suited for further drug development, and AM2389 currently is used to probe behavioral consequences of sustained ECS activation.

Cannabinergic aminoalkylindoles, including AM678=JWH018 found in 'Spice', examined using drug (Δ(9)-tetrahydrocannabinol) discrimination for rats

We examined four different cannabinergic aminoalkylindole ligands, including one drug (AM678=JWH018) found in herbal 'Spice' concoctions, for their ability to substitute for Δ(9)-tetrahydrocannabinol (THC), and the ability of the cannabinoid receptor 1-selective antagonist/inverse agonist rimonabant to block the substitution, 30 and 90 min after intraperitoneal injection. Rats trained to discriminate the effects of vehicle from those produced by 3 mg/kg of THC were used. The order of potency was: AM5983≥AM678>AM2233>WIN55212-2 at both test intervals. AM5983 and AM678 appeared eight times more potent than THC, followed by AM2233 (about twice as potent as THC), and WIN55212-2 approximately THC at the 30-min test interval. The aminoalkylindoles showed reduced potency (i.e. an increased ED50 value) at the longer injection-to-test interval of 90 min compared with testing at 30 min. The rightward shifts by coadministration of rimonabant were approximately 8-fold to 12-fold for AM5983 and AM678, compared with an approximately 3-fold rightward shift for the WIN55212-2 curve. AM2233 (1.8 mg/kg) substitution was also blocked by 1 mg/kg of rimonabant. In conclusion, AM5983 and AM678=JWH018 are potent cannabimimetics derived from an aminoalkylindole template. WIN55212-2 seemed to interact differently with rimonabant, compared with either AM5983 or AM678, indicating potential differences in the mechanism(s) of action among cannabinergic aminoalkylindoles.

Discriminative stimulus functions in rats of AM1346, a high-affinity CB1R selective anandamide analog

OBJECTIVE

To characterize in vivo the high-affinity CB(1) cannabinoid receptor (CB(1)R) selective anandamide analog AM1346 [alkoxyacid amide of N-eicosa-tetraenylamine] using drug discrimination. Substitution tests involved Delta(9)-tetrahydrocannabinol (Delta(9)-THC) and R-(+)-methanandamide (mAEA), a metabolically stable analog of anandamide (AEA), as well as the CB(1)R antagonist/inverse agonist rimonabant; D: -amphetamine and morphine were also examined to assess pharmacological specificity.

MATERIALS AND METHODS

Rats were initially trained to discriminate between i.p.-injected vehicle and 3 mg/kg AM1346 (group 3 mg/kg; t' = 20 min); subsequently, the rats were retrained with 5.6 mg/kg AM1346 (group 5.6 mg/kg; t' = 20 min).

RESULTS

Dose-generalization curves of AM1346, Delta(9)-THC, and mAEA suggested the following order of potency: Delta(9)-THC > AM1346 > mAEA both for rats discriminating between 3 and 5.6 mg/kg AM1346 from vehicle. In group 3 mg/kg, challenge by 1 mg/kg rimonabant resulted in parallel shifts to the right of the dose-generalization curves for Delta(9)-THC and AM1346, suggesting surmountable antagonism. Surmountable antagonism was not demonstrated with rimonabant-mAEA combinations. A long duration of effect was indicated when 3 mg/kg AM1346 was examined after different time intervals following i.p. administration (group 3 mg/kg). The in vivo half-life was close to 5 h. Neither D: -amphetamine nor morphine generalized in either of groups 3 mg/kg and 5.6 mg/kg, suggesting pharmacological specificity.

CONCLUSION

Unlike mAEA, the surmountable antagonism between rimonabant and AM1346 showed that the structural features of AEA can be modified to produce novel ligands that reduce the dissociation between the discriminative stimulus and rate decreasing effects of CB(1)R agonists derived from an AEA template.

Divergent effects of cannabidiol on the discriminative stimulus and place conditioning effects of Delta(9)-tetrahydrocannabinol

Cannabis sativa (marijuana plant) contains myriad cannabinoid compounds; yet, investigative attention has focused almost exclusively on Delta(9)-tetrahydrocannabinol (THC), its primary psychoactive substituent. Interest in modulation of THC's effects by these other cannabinoids (e.g., cannabidiol (CBD)) has been stimulated anew by recent approval by Canada of Sativex (a 1:1 dose ratio combination of CBD:THC) for the treatment of multiple sclerosis. The goal of this study was to determine the degree to which THC's abuse-related effects were altered by co-administration of CBD. To this end, CBD and THC were assessed alone and in combination in a two-lever THC discrimination procedure in Long-Evans rats and in a conditioned place preference/aversion (CPP/A) model in ICR mice. CBD did not alter the discriminative stimulus effects of THC at any CBD:THC dose ratio tested. In contrast, CBD, at CBD:THC dose ratios of 1:1 and 1:10, reversed CPA produced by acute injection with 10mg/kg THC. When administered alone, CBD did not produce effects in either procedure. These results suggest that CBD, when administered with THC at therapeutically relevant ratios, may ameliorate aversive effects (e.g., dysphoria) often associated with initial use of THC alone. While this effect may be beneficial for therapeutic usage of a CBD:THC combination medication, our discrimination results showing that CBD did not alter THC's discriminative stimulus effects suggest that CBD:THC combination medications may also produce THC-like subjective effects at these dose ratios.

Discriminative stimulus functions of AM-1346, a CB1R selective anandamide analog in rats trained with Delta9-THC or (R)-methanandamide (AM-356)

OBJECTIVE

To characterize in vivo the high-affinity cannabinoid CB1 receptor (CB1R) selective anandamide analog AM-1346 [alkoxyacid amide of N-eicosa-tetraenylamine] using drug discrimination procedures. D-amphetamine and also morphine in the (R)-methanandamide-trained group (see below) were examined to assess pharmacological specificity.

METHODS

Three groups of rats were trained to discriminate between vehicle and (1) 1.8 mg/kg Delta9-tetrahydrocannabinol (Delta9-THC); (2) 5.6 mg/kg Delta9-THC; and (3) 10 mg/kg (R)-methanandamide (AM-356; a metabolically stable analog of anandamide). Delta9-THC was given i.p. 30 min and (R)-methanandamide 15 min before training.

RESULTS

AM-1346 generalized to all three training conditions, both at 15 and 30 min after administration. The rank order potency was: Delta9-THC > AM-1346 > (R)-methanandamide. AM-1346 appeared slightly more potent 30 min compared to 15 min postadministration. In the presence of 0.3 mg/kg of the CB1R antagonist/inverse agonist SR-141716A, the dose generalization curves of Delta9-THC and AM-1346 resulted in parallel shifts to the right in the 1.8 mg/kg Delta9-THC-trained group. A long duration of action for AM-1346 (relative to AM-356) was indicated in tests where AM-1346 was examined in the 5.6 mg/kg Delta9-THC-trained group. Neither D-amphetamine, nor morphine generalized in either of the groups, suggesting pharmacological specificity.

CONCLUSION

Unlike (R)-methanandamide, the surmountable antagonism between SR-141716A and AM-1346 shows that the structural features of anandamide can be modified in ways that reduce the dissociation between the discriminative stimulus and rate decreasing effects of CB1R agonists derived from an anandamide template.

Systemic or intrahippocampal cannabinoid administration impairs spatial memory in rats

The purpose of the present study was to investigate the disruptive effects of cannabinoids on working memory as assessed in the eight-arm radial-maze. Systemic administration of delta 9-THC, WIN-55,212-2, and CP-55,940 increased the number of errors committed in the radial-maze. CP-55,940 was the most potent cannabinoid in impairing memory (ED50 = 0.13 mg/kg). delta 9-THC and WIN-55,212-2 disrupted maze-choice accuracy at equipotent doses (ED50 values = 2.1 and 2.2 mg/kg, respectively). In addition, systemic administration of each of these agents retarded completion time. Whereas the doses of delta 9-THC and CP-55,940 required to retard maze performance were higher than those needed to increase error numbers, WIN-55,212-2 was equipotent in both of these measures. On the other hand, neither anandamide, the putative endogenous cannabinoid ligand, nor cannabidiol, an inactive naturally occurring cannabinoid, had any apparent effects on memory. A second aim of this study was to elucidate the neuroanatomical substrates mediating the disruptive effects of cannabinoids on memory. Intrahippocampal injections of CP-55,940 impaired maze performance in a dose-dependent manner (ED50 = 8 micrograms/rat), but did not retard the amount of time required to complete the maze. The effects of intrahippocampal CP-55,940 were apparently specific to cognition because no other cannabinoid pharmacological effects (e.g., antinociception, hypothermia, and catalepsy) were detected. This dissociation between choice accuracy in the radial-maze and other cannabinoid pharmacological effects suggests that the working memory deficits produced by cannabinoids may be mediated by cannabinoid receptors in the hippocampus.

Discriminative stimulus- and open-field effects of the enantiomers of 11-hydroxy-delta-8-tetrahydrocannabinol in pigeons and gerbils

The cannabimimetic activity of the two enantiomers of 11-hydroxy-delta-8-tetrahydrocannabinol (11-OH-delta-8-THC) was evaluated in pigeons trained to discriminate between the presence and absence of (-)-delta-9-tetrahydrocannabinol [(-)-delta-9-THC]. (-)-11-OH-Delta-8-THC exhibited cannabimimetic activity with a potency (ED50, 0.17 mg/kg) similar to that of delta-9-THC. The duration of action for (-)-11-OH-delta-8-THC was shorter than that observed for delta-9-THC. No cannabimimetic activity was seen after administrations of (+)-11-OH-delta-8-THC, indicating enantiomeric selectivity for the discriminable effects. A dose-related decrease in response rate occurred with (-)-11-OH-delta-8-THC, but not with (+)-11-OH-delta-8-THC; the latter compound produced an increase in responding at 3 mg/kg. Open-field behavior in Mongolian gerbils indicated marked suppression of rearing (vertical activity) after treatments with (-)-delta-9-THC and (-)-11-OH-delta-8-THC; this did not occur after (+)-11-OH-delta-8-THC. The results support the notion of cannabimimetic enantiospecificity.

Delta 9-tetrahydrocannabinol discrimination in rats as a model for cannabis intoxication

Studies of the discriminative stimulus effects of delta 9-THC are reviewed. The results of generalization studies in rats trained to discriminate delta 9-THC from nondrug provide evidence for the pharmacological specificity of the delta 9-THC stimulus. Only cannabinoid analogs of delta 9-THC substitute fully for delta 9-THC. The ability of cannabinoids to produce delta 9-THC-like discriminative stimulus effects appears to predict delta 9-THC- or marihuana-like effects in humans. Of the 11 cannabinoids tested in rats and humans, the results with 9 are in complete concordance, and results with the remaining two are inconclusive. This concordance provides evidence for the validity of delta 9-THC discrimination in rats as an animal model of cannabis intoxication. A number of natural and synthetic cannabinoids have delta 9-THC-like discriminative stimulus effects. They represent a 5,600-fold range of relative potencies. Micromolar potency estimates and relative potencies to delta 9-THC for these compounds are provided. Correlations between these values and potencies for cellular actions of cannabinoids can be used to establish the neural substrates of cannabis intoxication.

A random walk through a cannabis field

The present overview covers various aspects of research going on in the Cannabis field in the Department of Natural Products at the Hebrew University. In the first part we discuss, and try to explain, the reason for the absence of the term Cannabis (and possibly also opium) in the Old Testament. In the second part we bring evidence that, contrary to widely held views, stereospecificity of cannabinoid action is extremely high, and in certain cases almost absolute. Previous results seem to have been due to impurities in the samples tested. (+)-Delta-1-THC, (+)-delta-6-THC and (+)-7-hydroxy-delta-6-THC, when purified sufficiently, exhibit activity of about 1% of that of the natural (-) enantiomers. A new labelled cannabinoid ligand has been prepared by catalytic reduction of (-)-7-hydroxy-delta-6-THC dimethylheptyl. The equatorial C-1 epimer obtained binds to the cannabinoid receptor with a KI of 40 pM. This compound is one of the most active cannabinoids tested so far for binding to the canabinoid receptor, and may become an important tool in cannabinoid research.

The molecular basis of cannabinoid activity

Cannabinoids have been known to exhibit a wide variety of biological effects. Over the past fifty years numerous analogs were synthesized in an attempt to understand the structural requirements for each cannabinoid activity. Only recently, however, some important findings have focused new attention on this field of research. These findings include: (a) The development of novel "non-classical" potent cannabinoid analogs which exhibit similar pharmacological profiles with their "classical" counterparts; (b) The demonstration that there are specific cannabinoid binding sites in cell cultures as well as in mammalian brains; (c) Biophysical studies related to the interactions of cannabinoids with membranes which lead to a better understanding of those molecular properties which are required for cannabinoid activity; (d) Detailed and uniform pharmacological testing on a sizeable number of analogs allowing for a more detailed dissection of the cannabinoid effects and respective "structure activity relationships." The newly increased interest in cannabinoid research opens the door for a better understanding and potential treatment in cases of abuse as well as novel therapeutic opportunities through the design and synthesis of pharmacologically more selective analogs.

Separation of the discriminative stimulus effects of stereoisomers of delta 2- and delta 3-tetrahydrocannabinols in pigeons

Pigeons, trained to discriminate between the presence or absence of delta 1-tetrahydrocannabinol (THC) (I) (0.56 mg/kg), were tested with (1S,4R)-delta 2-THC (II) (1-17.5 mg/kg), with the C-1 epimers of (4R)-delta 2-THC acetate, namely (1S,4R)-delta 2-THC acetate (IIIA) (3-17.5 mg/kg) and (1R,4R)-delta 2-THC acetate (IIIB) (1-17.5 mg/kg) and with the enantiomers of delta 3-THC acetate, namely (1S)-delta 3-THC acetate (IVA) (1-10 mg/kg) and (1R)-delta 3-THC acetate (IVB) (3-30 mg/kg). The results indicated that (I) was considerably more potent than any of the other compounds evaluated (ED50 of compound I = 0.18 and 0.25 mg/kg at the two post-injection intervals examined, 90 and 270 min, respectively). Furthermore, of the two delta 2-THC acetates, compound (IIIB) was active whereas compound (IIIA) was not in comparable doses. The parent phenol of compound (IIIA), namely (II), was also inactive. Comparison of the pair of enantiomers, (IVA) and (IVB), showed the former to be significantly more potent than the latter. We have thus shown that the delta 1-THC-like cue properties are separated in the stereoisomers of delta 2- and delta 3-THC.

Enantiomeric cannabinoids: stereospecificity of psychotropic activity

The 1,1-dimethylheptyl homolog of (-)-(3R,4R)-7-hydroxy-delta-6- tetrahydrocannabinol (compound II) is highly psychotropic in mice, rats and pigeons. The (+)-(3S,4S) enantiomer (III) was found to be psychotropically inactive at doses up to several thousand times those of the ED50 of (II).