Tricyclic Pyrazole-Based Compounds as Useful Scaffolds for Cannabinoid CB1/CB2 Receptor Interaction.

Abstract

Cannabinoids comprise different classes of compounds, which aroused interest in recent years because of their several pharmacological properties. Such properties include analgesic activity, bodyweight reduction, the antiemetic effect, the reduction of intraocular pressure and many others, which appear correlated to the affinity of cannabinoids towards CB₁ and/or CB₂ receptors. Within the search aiming to identify novel chemical scaffolds for cannabinoid receptor interaction, the CB₁ antagonist/inverse agonist pyrazole-based derivative rimonabant has been modified, giving rise to several tricyclic pyrazole-based compounds, most of which endowed of high affinity and selectivity for CB₁ or CB₂ receptors. The aim of this review is to present the synthesis and summarize the SAR study of such tricyclic pyrazole-based compounds, evidencing, for some derivatives, their potential in the treatment of neuropathic pain, obesity or in the management of glaucoma.

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Keywords: tricyclic pyrazoles, structure-activity relationship, CB₂ agonist, CB₁ agonist, CB₁ neutral antagonist, anti-nociceptive activity, glaucoma, obesity

Article notes

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Received 2021 Mar 3; Accepted 2021 Mar 29; Collection date 2021 Apr.

Author notes

1. Introduction

Cannabinoids are a class of different chemical compounds (Figure 1), including the endocannabinoids (produced naturally in the body by humans and animals such as anandamide and 2-arachidonoylglycerol), the phytocannabinoids (derived from Cannabis, exemplified by Δ⁹-tetrahydrocannabinol, the major psychoactive component of Cannabis sativa, commonly known as marijuana), and the synthetic cannabinoids (produced chemically by human, comprising a wide array of chemical entities, i.e., the pyrazole-based compounds SR141716A and SR144528 and the indole based compound WIN-55,212-2) [1,2,3]. The physiological and behavioral effects of cannabinoids appear directly correlated to their affinity towards two different classes of specific receptors: CB₁ receptors located predominantly in the central nervous system [4], and CB₂ receptors which are mostly found in peripheral tissues [5]. In the brain, the CB₁ receptors are abundantly expressed in the hippocampus, cerebellum and striatum [6,7]. Among the peripheral tissues wherein the CB₁ receptors have been found, the enteric nervous system [8], testis, urinary bladder, vas deferens can be mentioned [9]. CB₁ receptor mRNA and protein have been furthermore identified in the rat and human eye, both in the retina and in the iris, and in the ciliary body [10]. CB₂ receptors are located in the marginal zones of the spleen, tonsils, immune cells [9,11] and to a much lesser extent in CNS [12]. Furthermore, CB₂ receptor mRNA was expressed in the adult rat retina, including the somas of retinal ganglion cells [13].

Figure 1Chemical structure of representative cannabinoids.

During the last years, several ligands endowed with high affinities and subtype selectivity for both receptors were identified. Such ligands were proposed as potential therapeutic targets for the treatment of several diseases, including neuropathic pain [14], cancer [15,16] and osteopor4osis [17].

Non-selective CB₁/CB₂ receptor agonists are the constituents of some approved medicines, i.e., Sativex^®, Cesamet^®, Marinol^®. Sativex contains approximately equal amounts of Δ⁹-tetrahydrocannabinol and the non-psychoactive phytocannabinoid cannabidiol, and is prescribed for neuropathic pain relief in adults with multiple sclerosis and as an adjunctive analgesic treatment for adult patients in advanced cancer [18]. Furthermore, the relevance of CB receptors as an emerging target of pharmacotherapy is documented also by the discovery of mixed CB₁/CB₂ receptor agonists as antiglaucoma agents [19].

The only cannabinoid receptor antagonist approved as a medicine to-date is the CB₁ antagonist/inverse agonist SR141716A (rimonabant, Acomplia^®, Figure 1). This compound has been developed for the treatment of obesity and related metabolic risk factors [20]. However, it was soon withdrawn for its serious psychiatric disorders including anxiety, depression and suicidal tendency. Although most pharmaceutical companies were deterred from developing a drug that displayed rimonabant-like CB₁ receptor antagonist/inverse agonist activity for the management of any disorders, this compound still remains an extremely valuable lead for the design of new ligands for CB receptors interaction [21,22]. Within this frame, the 4-alkyl-5-arylpyrazole skeleton of rimonabant has been modified, leading to benzocycloalkylpyrazole-based tricyclic systems of general formula I-IV (Figure 2). Modifications carried out on such scaffolds, allowed to accede to further pyrazole-based tricyclic systems of general formula V-XVII (Figure 2). Fine tuning of these tricyclic systems (vide infra) allowed to identify hundreds of molecules, most of which endowed with high affinity and selectivity for CB₁ or CB₂ receptors. In this review, pyrazole-based tricyclic compounds I-XVII are divided into four main groups according to the size of the central ring connected to the pyrazole one. If a five-membered ring is connected to the pyrazole, the compound belongs to (5,5)-condensed pyrazole derivatives, and if the connected ring is a six-, seven- or eight-membered ring, the compound belongs to (5,6)-, (5,7)- or (5,8)-condensed pyrazole derivatives. Here, we briefly present the synthesis and the bioactivities of pyrazole-based tricyclic compounds I-XVII investigated by us and other groups. Furthermore, this review surveys chemical and biological literature of some miscellaneous molecules featuring tricyclic pyrazole structure closely related to compounds I-XVII, investigated for cannabinoid receptor affinity.

Design of cannabinoid CB1/CB2 receptor ligands. — Figure 2Design of cannabinoid CB₁/CB₂ receptor ligands.

2. (5,5)-Condensed Pyrazole Derivatives

2.1. 1,4-dihydroindeno(1,2-c)pyrazole-Based Derivatives

The first (5,5)-condensed pyrazole derivatives synthesized by us for cannabinoid receptors interaction are those of general formula I (Figure 2) featuring the 1,4-dihydroindeno(1,2-c)pyrazole core. These compounds were designed as rigid analogs of CB₁ antagonist/inverse agonist SR141716A (rimonabant), endowed with a high affinity for CB₁ receptors and good selectivity over CB₂ receptors. It has been proposed that minimization of the flexibility of the lead compound through the introduction of structural constraints could have some impact on cannabinoid receptor interaction, maybe allowing the ligand to bind with high affinity and selectivity to its receptor. Accordingly, the first series of 1,4-dihydroindeno(1,2-c)pyrazole derivatives have been synthesized and evaluated for their in vitro binding affinities for CB₁ and CB₂ receptors. Most of these compounds are N-piperidine-carboxamides that differ for R substituent (Cl, F, I, CH₃, OCH₃), whereas G, quite often, maintained the 2,4-Cl-phenyl substitution pattern of rimonabant [23].

Compounds I were synthesized starting from the appropriate ketones 1 (Scheme 1) which were α-acylated by Claisen reaction, furnishing 1,3-diketoesters 2 as a tautomeric equilibrium shifted towards the alkenylidene structure (2′). The cyclization with appropriate hydrazines in refluxing EtOH gave the tricyclic dihydroindeno(1,2-c)pyrazole esters 3, which were hydrolyzed with KOH, affording the corresponding acids 4. Target compounds I were synthesized by condensation of acids 4, previously activated to acyl chlorides with SOCl₂, with the appropriate amines.

Scheme 1General synthetic route for the preparation of compounds I.

If not otherwise stated, the four-step general synthetic route for I compounds, with minor changes, was employed for the preparation of all compounds of general formula II-XVII, starting from the appropriate ketones and using the appropriate hydrazines and amines.

Our first SAR study revealed that several compounds incorporating the planar 1,4-dihydroindeno(1,2-c)pyrazole scaffold displayed very high in vitro binding affinity for CB₂ receptors comparable to, or exceeding, that of SR144528 (Figure 1), identified as the first highly potent and selective ligand for the CB₂ receptors. Representative derivatives are IAaX, IAhX, IAfX, IBaX (Figure 3), compound IAhX emerging for its high affinity for CB₂ receptors and exceptional selectivity over CB₁ receptor (CB₁/CB₂ selectivity ratio of 9811).

Structure of representative 1,4-dihydroindeno(1,2-c)pyrazoles (I). Affinities at CB1 and CB2 receptors were assessed by competition of (3H)-CP 55,940 in mouse cerebellum membranes and in mouse spleen homogenates, respectively [23]. Permission has been obtained and there is no copyright issue. — Figure 3Structure of representative 1,4-dihydroindeno(1,2-c)pyrazoles (I). Affinities at CB₁ and CB₂ receptors were assessed by competition of (³H)-CP 55,940 in mouse cerebellum membranes and in mouse spleen homogenates, respectively [23]. Permission has been obtained and there is no copyright issue.

Our results prompted us to investigate new 1,4-dihydroindeno(1,2-c)pyrazoles (I), which were obtained modifying the N-carboxamide moiety (Q) and the aryl substitution of the lead compounds IAaX and IAhX [24]. In general, our SAR study showed that the CB₁ receptor affinities of all the investigated compounds were lower than their CB₂ receptor affinities, evidencing the suitability of 1,4-dihydroindeno(1,2-c)pyrazole architecture to generate ligands for CB₂ receptor interaction. Representative compounds of this series are IDhX, IEhX, IFhX, IGhX (Figure 4), all displaying high CB₂ affinity and reasonable selectivity over CB₁ receptors, even if lower than that elicited by compounds IAaX and IAhX.

Structure of representative 1,4-dihydroindeno(1,2-c)pyrazoles (I) obtained by modification of carboxamide moiety of compound IAhX. Affinities at CB1 and CB2 receptors were assessed by competition of (3H)-CP 55,940 in mouse cerebellum membranes and in mouse spleen homogenates, respectively [24]. — Figure 4Structure of representative 1,4-dihydroindeno(1,2-c)pyrazoles (I) obtained by modification of carboxamide moiety of compound **IAhX**. Affinities at CB₁ and CB₂ receptors were assessed by competition of (³H)-CP 55,940 in mouse cerebellum membranes and in mouse spleen homogenates, respectively [24].

In vitro CB₂ intrinsic activity evaluation assay, based on the determination of P-ERK 1/2 increasing expression in human promyelocitic leukemia HL-60 cells exposed to the compounds to be assayed, highlighted agonist activity toward CB₂ receptors for derivatives IDhX, IEhX and for prototype IAaX, IAhX. In particular, the tested compounds significantly increased P-ERK 1/2 expression, reaching the maximum effect at the concentration of 10 nM with the following values: +61.3 ± 12.4% (IDhX), +125.0 ± 35.8% (IEhX), +65.0 ± 18.5% (IAaX), +83.0 ± 4.2% (IAhX) versus vehicle. Overall, the effect of tested compounds as CB₂ agonists was specific as it was blocked by the CB₂ receptor antagonist SR144528 [24].

By pursuing our interest in expanding SAR studies around 1,4-dihydroindeno(1,2-c)pyrazole core, especially in the light of the potential of CB₂ ligands for the treatment of immune disorders or as anti-nociceptive agents [14,25], novel derivatives have been designed, making use of molecular hybridization based on scaffold hopping [26]. In particular, based upon the putative interacting sites and structural features of selective CB₂ antagonist SR144528 (Figure 1), i.e., N₁-benzyl group, the C₃ carboxamide moiety, and the substitution of the C₅ phenyl ring [26,27], it was postulated that the introduction of such pharmacophoric elements in the tricyclic core of compound IAhX might provide new CB₂ ligands with potential therapeutic value. Briefly, different synthesized compounds were monoterpene derivatives incorporating bulky groups in the carboxamide moiety (i.e., fenchyl-, bornyl-, isopinocampheyl-, myrtanyl-, menthyl-), bearing a 6-CH₃,7-Cl or 6-Cl,7-CH₃ substitution pattern at the aryl ring of 1,4-dihydroindeno(1,2-c)pyrazole core. Some adamantane derivatives were also investigated, together with compounds incorporating simple cycloalkyl motifs at the carboxamide moiety. Compounds IAjX, IAkX, IHjX, IIjX, IKjX, IDjX, IDkX, IHkX (Figure 5) are representatives of these third series of I compounds. As described above for representative compounds depicted in Figure 3 and Figure 4, our SAR study carried out on a third series of molecules, evidenced for 1,4-dihydroindeno(1,2-c)pyrazole-based molecules preferential affinity for CB₂ receptors. However, the introduction of a chlorine atom, as well as its exchange with the methyl group in all-new hybrid compounds seemed to play a modest role in lowering the levels of CB₂-affinity as compared to the reference compounds IAaX and IAhX.

Structure of representative 1,4-dihydroindeno(1,2-c)pyrazoles (I) designed making use of molecular hybridization based on scaffold hopping. Affinities at CB1 and CB2 receptors were assessed by competition of (3H)-CP 55,940 in mouse cerebellum membranes and in mouse spleen homogenates, respectively [26]. — Figure 5Structure of representative 1,4-dihydroindeno(1,2-c)pyrazoles (I) designed making use of molecular hybridization based on scaffold hopping. Affinities at CB₁ and CB₂ receptors were assessed by competition of (³H)-CP 55,940 in mouse cerebellum membranes and in mouse spleen homogenates, respectively [26].

According to previous data obtained for compounds IAaX, IAhX, IDhX and IEhX, analogs IIjX, IDjX and IHkX, endowed with the highest affinity for CB₂ receptors, exhibited CB₂ agonism activity in in vitro model based on the determination of P-ERK 1/2 increasing expression in HL-60 cells, with maximum values reached at 125 nM for compounds IIjX (+54.5 ± 12.1%) and IDjX (+82.5 ± 19.1%), and at 50 nM for compound IHkX (+46.4 ± 15.6%) versus vehicle. Furthermore, the effect of such tested compounds on P-ERK ½ expression was counteracted by the reference CB₂ antagonist AM630, suggesting the correspondence between the detected effect and CB₂ modulation.

The obtained data confirmed that the flattening of 1,4-dihydroindeno(1,2-c)pyrazole core is important to assure agonist rather than antagonist activity, with respect to not condensed and more flexible analogs such as the antagonist SR144528.

Within this frame, a series of compounds incorporating the 1,4-dihydroindeno(1,2-c)pyrazole scaffold (I), sharing the N₁-benzyl group and bulky groups in the carboxamide moiety (i.e., IOkW, Figure 2) were claimed by Sanofi-Aventis, but no specific biological activity was presented [28]. However, the compounds of the invention were generally described as potent and selective CB₂ receptor antagonists with Ki values < 5 × 10⁻⁷ M. Antagonistic properties of such compounds have been demonstrated by the results in the models for inhibition of adenylate cyclase induced by forskolin, although no specific examples or data were disclosed.

Furthermore, 1,4-dihydroindeno(1,2-c)pyrazoles featuring a cyclopropyl or cyclohexyl building block in C₆ position were investigated by us, in order to evaluate the effect of cycloalkyl moiety in place of methyl group both on cannabinoid receptor binding and activity [29]. The most interesting compounds coming from this fourth series are depicted in Figure 6. Whereas, these analogs provided further insight regarding the structural features for CB₂ affinity and selectivity, our data evidenced that the introduction of a cyclopropyl moiety in most of the synthesized compounds seemed to play a modest role in lowering the CB₂ receptor affinity, especially if compared to compound IAhX. Interestingly, intrinsic activity for compounds IAlX, IHlX, ILlX, IJlX, evaluated by GTPγS binding assay, showed antagonist/inverse agonist properties (IC₅₀ for compound IAlX = 294 nM, for IHlX = 80 nM, for ILlX = 27 nM and for IJlX = 51 nM).

Structure and CB1/CB2 binding affinities of representative cyclopropyl-based 1,4-dihydroindeno(1,2-c)pyrazoles (I). Affinities at CB1 and CB2 receptors were evaluated by competition of (3H)-CP 55,940 in human CB1 or CB2 receptors transfected into HEK293 EBNA cells [29]. — Figure 6Structure and CB₁/CB₂ binding affinities of representative cyclopropyl-based 1,4-dihydroindeno(1,2-c)pyrazoles (I). Affinities at CB₁ and CB₂ receptors were evaluated by competition of (³H)-CP 55,940 in human CB₁ or CB₂ receptors transfected into HEK293 EBNA cells [29].

Independently, other groups investigated the biological properties of some 1,4-dihydroindeno(1,2-c])pyrazoles synthesized by our group. In particular, within the search aiming to characterize the molecular pharmacology of the most widely used CB₂ receptor ligands, it was reported for compound IAhX, namely Gp-1a, an affinity for the CB₂ receptors markedly different from that reported by our group (K_i CB₁ = 426 ± 0.08 nM, K_i CB₂ = 20.9 ± 0.23 nM; CB₁/CB₂ selectivity ratio = 20), using (³H)CP-55,940 and mouse brain and spleen as source for CB₁ and CB₂ receptors, respectively [30]. Furthermore, in contrast to our results, the same authors reported for Gp-1a inverse agonist properties on CB₂ receptors in GTPγS assay and resulted not active in hCB₂ receptor pERK assay [30]. Indeed, the first two series of 1,4-dihydroindeno(1,2-c)pyrazole-based compounds synthesized by our group [23,24], including Gp-1a, were described in a patent application providing methods and pharmaceutical compositions for reducing the serum level of immunoglobulin IgE in an animal or human subject [31]. In particular, it was reported the CB₂ agonist Gp-1a attenuated the serum levels of total IgE from BALB/e mice and the co-treatment with the CB₂ antagonist SR144528 reversed the Gp-1a effect. Therefore, the patent provided a method for modulating this type of antibody for the treatment of immune system-related conditions such as allergy, hay fever and the like. Biological literature concerning Gp-1a pointed out the relevance of such a compound as a useful pharmacological tool to ascertain in more detail the role of CB₂ receptors in physiopathological conditions [32,33,34,35,36]. Furthermore, the pharmacological relevance of 1,4-dihydroindeno(1,2-c)pyrazole-based I compounds emerged also from the significant anti-nociceptive activity of the potent and selective CB₂ agonist IDhX, namely NESS400, in Spared Nerve Injury (SNI) neuropathic mice, by alleviating both mechanical allodynia and thermal hyperalgesia [37].

2.2. Benzofuro(3,2-c)pyrazol-Based Derivatives (V)

Further condensed (5,5)-pyrazole derivatives were designed by us making use of bioisosteric replacement as drug design approach to obtain novel planar tricyclic scaffold for cannabinoid receptor interaction [38]. Following this approach, a new series of 1,4-dihydroindeno(1,2-c)pyrazole analogs, namely benzofuro(3,2-c)pyrazoles (V, Figure 2), containing an oxygen atom at position 4 instead of a methylene unit, were designed. The structure of representative compounds is depicted in Figure 7. These compounds were previously described by Neuroscienze Pharmaness S.C.A.R.L in a patent application claiming specific composition of microemulsions of pharmaceutical compounds. Indeed, the patent covers a more extensive series of tricyclic pyrazoles belonging both to (5,5) as well as (5,6) and (5,7]) series [39].

Structure of representative benzofuro(3,2-c)pyrazol-based derivatives (V). Affinities at CB1 and CB2 receptors were assessed by competition of (3H)-CP 55,940 in mouse cerebellum membranes and in mouse spleen homogenates, respectively [38]. — Figure 7Structure of representative benzofuro(3,2-c)pyrazol-based derivatives (V). Affinities at CB₁ and CB₂ receptors were assessed by competition of (³H)-CP 55,940 in mouse cerebellum membranes and in mouse spleen homogenates, respectively [38].

In general, our SAR study revealed high CB₂ receptor affinity for the new compounds, with values qualitatively similar with those of compound IDhX, as well as those of related analogs incorporating the 1,4-dihydroindeno(1,2-c)pyrazole skeleton. In contrast, a comparison of K_iCB₂ value of compound IAhX and that of the analog VAhX revealed two orders of magnitude decreased affinity for VAhX. Compounds VLhX and VMhX, featuring a bornyl and isopinocampheyl moiety at the carboxamide portion, exhibited the best CB₂ cannabinoid binding profiles among all synthesized derivatives. CB₂ functional assay carried out on HL-60 cells, based on the evaluation of P-ERK1/2 expression induced by cannabinoid ligands, evidenced agonism behavior for all synthesized compounds [38], with calculated maximum values, in most cases, exceeding that of the agonist WIN-55,212-2 (i.e., VAhX: dose 50 nM, 205 ± 12%; VDhX, dose 50 nM, 196 ± 20%; VLhX: dose 10 nM, 189 ± 11%; VMhX: dose 5 nM, 205 ± 6%; WIN-55,212-2: dose 75 nM, 190 ± 17% versus vehicle). Overall, the effect of tested compounds as CB₂ agonists was specific as it was blocked by the CB₂ receptor antagonist AM630 [38].

2.3. 1,4-Dihydrothieno(2′,3′-4,5)cyclopenta(1,2-c)pyrazole-Based Derivatives (VII) and 1,4-Dihydrothieno(3′,2′-4,5)cyclopenta(1,2-c])pyrazole-Based Derivatives (X)

To further investigate the versatility of (5,5)-pyrazole condensed tricyclic derivatives in the development of CB₂ ligands as therapeutic agents, our attention was focused on the benzene ring of the tricyclic indenopyrazole scaffold (I), by replacing it with a thiophene ring, giving rise the novel dihydrothienocyclopentapyrazole architecture which fine-tuning furnished novel derivatives with general formula VII (Figure 2). It was postulated that bioisosteric replacement benzene/thiophene could be an efficient strategy to develop novel CB₂ selective ligands and maybe provide further insight concerning structural features for cannabinoid receptor interaction [40]. In our SAR study, we planned to investigate the effect of changing the size of carboxamide moiety (Q), of methyl shifting from C₆ to C₇ of the tricyclic platform, as well as the effect related to the replacement of the N₁-dichlorophenyl group (X) with p-methylbenzyl moiety (Z) on cannabinoid receptor affinity. The structure of representative compounds is depicted in Figure 8. The major term, compound VIIAhX, displayed a high affinity for CB₂ receptors, even if 62-fold decreased with respect to the reference compound IAhX with selectivity ratio K_i CB₁/K_i CB₂ = 191. A similar trend was observed in several thienocyclopentapyrazole compounds (Figure 8) with the exception of VIINhX, which exhibited a mixed binding profile, reaching K_i values of 6.5 and 5.1 nM for CB₁ and CB₂, respectively. All these compounds profiled as full agonists at CB₂ receptors in an assay based on the determination of P-ERK 1/2 increasing expression in HL-60 cells [40].

Structure of representative 1,4-dihydrothieno(2′,3′-4,5)cyclopenta(1,2-c)pyrazole-based derivatives (VII). Affinities at CB1 and CB2 receptors were assessed by competition of (3H)-CP 55,940 in mouse cerebellum membranes and in mouse spleen homogenates, respectively [40]. — Figure 8Structure of representative 1,4-dihydrothieno(2′,3′-4,5)cyclopenta(1,2-c)pyrazole-based derivatives (**VII**). Affinities at CB₁ and CB₂ receptors were assessed by competition of (³H)-CP 55,940 in mouse cerebellum membranes and in mouse spleen homogenates, respectively [40].

Within this framework, a series of 1,4-dihydrothieno(3′,2′-4,5)cyclopenta(1,2-c)pyrazole-based derivatives with general formula X (Figure 2) were investigated. Representative compounds are depicted in Figure 9. Such compounds were described by Neuroscienze Pharmaness S.C.A.R.L in a patent application encompassing a more extensive series of condensed tricyclic pyrazoles [41]. According to binding data, shifting the sulfur atom of the 1,4-dihydrothieno(2′,3′-4,5)cyclopenta(1,2-c)pyrazole structural template from position 5 to 7 induced a significant impact on cannabinoid receptor affinity. In general, most of the investigated compounds exhibited a preferential affinity for CB₂ receptors, with different compounds showing mixed and high CB₁/CB₂ cannabinoid receptor affinities (XIhZ, XNhZ, XHhX, XIhY, XIhX, XIgX, Figure 9).

Structure of representative 1,4-dihydrothieno(3′,2′-4,5)cyclopenta(1,2-c)pyrazole-based derivatives (X). Affinities at CB1 and CB2 receptors were assessed by competition of (3H)-CP 55,940 in mouse cerebellum membranes and in mouse spleen homogenates, respectively [41]. — Figure 9Structure of representative 1,4-dihydrothieno(3′,2′-4,5)cyclopenta(1,2-c)pyrazole-based derivatives (X). Affinities at CB₁ and CB₂ receptors were assessed by competition of (³H)-CP 55,940 in mouse cerebellum membranes and in mouse spleen homogenates, respectively [41].

Amongst the compounds claimed in the patent application, derivatives XIhZ, XNhZ, XHhX were investigated to evaluate their intrinsic activity as agonist or antagonist on CB₁ receptors in an ex-vivo model based on the use of the vas deferens. According to the behavior of WIN-55,212-2 and other CB₁ ligands in mice vas deferens isolated organ assay [42], compounds XIhZ, XNhZ, XHhX showed agonist activity, with XIhZ the most effective in inhibiting the contractions induced by an electric stimulus compared to the basal value, as evidenced by the reported dose-response curve [41].

Compounds XIhZ, XNhZ, XHhX were also investigated for their ability to reduce intraocular pressure (IOP) which is considered a prominent risk factor for glaucoma development and progression [43]. The first study highlighting the relevance of CB₁/CB₂ agonists for the treatment of glaucoma was conducted in 1971, reporting that smoking marijuana significantly lowered the IOP [44]. Very positive results were reported also for WIN-55,212-2, which is the prototype of the aminoalkylindole class of synthetic cannabinoids, activating both CB₁ and CB₂ receptors, albeit with a proclivity for the CB₂ receptors. In particular, in normotensive rabbits, a single dose of WIN-55,212-2, either topical or systemic, significantly reduced IOP without apparent ocular toxicity, most likely through effects on CB₁ receptors [45]. Subsequent studies showed a reduction of IOP in glaucomatous rats after local and chronic administration of WIN-55,212-2, without adverse effects [46]. These findings are consistent with another experiment showing that WIN-55,212-2 decreased IOP in human glaucoma resistant to conventional therapies [47]. Further studies have demonstrated increased aqueous outflow after exposure to the CB₂ agonist JWH015, suggesting a beneficial function derived from CB₂ receptor activation in the treatment of ocular diseases such as glaucoma [48]. Neuroprotective properties of cannabinoids have been demonstrated in CNS neurodegenerative diseases with different mechanisms [49]. Several studies have shown in the retina that CB₁ agonists (Δ⁹-tetrahydrocannabinol and cannabidiol) protected ganglion cells from glutamate-excitotoxicity and ischemia caused by increased IOP [50,51]. Although all these data are promising, an important issue for the clinical potential of cannabinoids as anti-glaucoma agents has been cardiovascular and psychotropic side effects mediated by systemic and brain cannabinoid receptor activation [52,53,54]. Additionally, short duration of action of cannabinoids on IOP reduction (i.e., the duration of action after smoking marijuana is only 3–4 h) is another issue that has to be overcome in the application of these compounds in treating glaucoma. Actually, standard therapeutic options in treating glaucoma include a few IOP-lowering drugs as prostaglandin analogs, β-adrenoreceptor antagonists, α₂-adrenoreceptor agonists, carbonic anhydrase inhibitors, and cholinergic agonists [55]. When medical therapy failed to lower IOP, laser or surgical interventions are extremely considered in order to prevent disease progression toward blindness.

According to unmet medical need, compounds XIhZ, XNhZ, XHhX, exhibiting high and mixed CB₁/CB₂ receptor affinities, with a proclivity for CB₂ subtype, and endowed of CB₁ agonist properties, according to the CB receptor profile of the reference cannabinoidergic compound WIN-55,212-2, by using the animal model of old DBA/2J mice, were investigated for their ability to reduce IOP [41]. Compounds XIhZ, XNhZ, XHhX and WIN-55,212-2, which was used as reference compound, were dispersed in the commercial emulsion Tocrisolve™ and applied to the eye of old DBA/2J mice at a concentration of 100 µg or 50 µg. The obtained results, reported in Table 1, showed that commercial emulsion Tocrisolve™ (20, 40 µL) had no effect on the IOP. Furthermore, at the dose of 100 µg, all tested compounds were effective in reducing eye pressure as the reference compound WIN-55,212-2, while only XIhZ, at the dose of 50 µg was more effective in reducing IOP than the reference compound. What is claimed in the patent application was pharmaceutical compositions comprising emulsions or microemulsions may be useful to avoid systemic side effects of such cannabinoid compounds. The preliminary results reported in the patent application [41] for compound XIhZ could pave the way for the development of novel cannabinoidergic compounds as anti-glaucoma agents.

Table 1Intraocular pressure (IOP) variation in old DBA/2J mice after administration of compounds XIhZ, XNhZ, XHhX and WIN-55,212-2 as reference compounds. The results are expressed as percent decrease of the IOP with respect to the animal basal IOP value [41].

	Intraocular Pressure Decrease (%)
Time of Administration	Carrier		XIhZ		XNhZ		XHhX		WIN-55,212-2
(Minutes)	20 µL	40 µL	50 µg	100 µg	50 µg	100 µg	50 µg	100 µg	50 µg	100 µg
30	0.1	0.3	15.9	23.9	2.9	22.2	3.0	16.6	4.3	23.1
60	−0.1	0.0	15.0	22.8	2.2	22.4	2.0	14.0	3.0	21.3
90	0.2	−0.2	12.6	19.6	0.8	25.0	0.5	11.2	2.0	18.1
120	0.0	0.0	11.7	21.7	1.5	16.7	11.7	21.7	1.9	13.2

2.4. 1,4-Dihydropyrazolo(3,4-a)pyrrolizine-Based Derivatives (XV)

Continuing with our interest in expanding SAR studies on cannabinoid receptors, and taking into consideration the binding profile of compounds IAaX and IAhX, a new tricyclic pyrazole scaffold, namely 1,4-dihydropyrazolo(3,4-a)pyrrolizine XV, was designed on the basis of bioisosteric replacement approach (benzene/pyrrole) [56]. Representative compounds are depicted in Figure 10. Surprisingly, none of the new compounds exhibited a high affinity for CB₂ receptors, with K_i values above 314 nM. Negligible affinity was also determined for CB₁ receptors, with XVIhX reaching the K_i value of 142 nM.

Structure of representative 1,4-dihydropyrazolo(3,4-a)pyrrolizine-based derivatives (XV). Affinities at CB1 and CB2 receptors were assessed by competition of (3H)-CP 55,940 in mouse whole-brain membranes and in CHO cell membranes transfected with hCB2 receptors [56]. — Figure 10Structure of representative 1,4-dihydropyrazolo(3,4-a)pyrrolizine-based derivatives (XV). Affinities at CB₁ and CB₂ receptors were assessed by competition of (³H)-CP 55,940 in mouse whole-brain membranes and in CHO cell membranes transfected with hCB₂ receptors [56].

3. (5,6)-Condensed Pyrazole Derivatives

3.1. 4,5-Dihydro-1H-benzo(g)indazole-Based Derivatives (II)

The first (5,6)-condensed pyrazole derivatives synthesized by us are those of general formula II (Figure 2), featuring the 4,5-dihydro-1H-benzo(g)indazole scaffold which is a homologue of 1,4-dihydroindeno(1,2-c)pyrazole one (compounds I). Representative compounds are depicted in Figure 11 [57]. Most of such compounds were described by Sanofi-Aventis in a patent application as cannabinoid CB₁ receptor antagonists, but no biological data were reported [58].

Structure of representative 4,5-dihydro-1H-benzo(g)indazole-based derivatives (II). Affinities at CB1 and CB2 receptors were assessed by competition of (3H)-CP 55,940 in mouse cerebellum membranes and in mouse spleen homogenates, respectively [57]. — Figure 11Structure of representative 4,5-dihydro-1H-benzo(g)indazole-based derivatives (II). Affinities at CB₁ and CB₂ receptors were assessed by competition of (³H)-CP 55,940 in mouse cerebellum membranes and in mouse spleen homogenates, respectively [57].

Interestingly, as evidenced by K_i values of compounds IIAbX and IIAiX with respect to compounds IAaX and IAhX, increasing the carbocyclic central ring size by one methylene unit (from (5,5)- to (5,6)-condensed pyrazole derivatives) involved a marked loss of affinity for CB₂ receptors, a significant increase in CB₁ affinity, and a consequent loss of CB₂ selectivity. A similar trend was exhibited by other derivatives incorporating such 4,5-dihydro-1H-benzo(g)indazole scaffold (i.e., IIAeX and IIBbX). The SAR study carried out on the two homologous series I and II, prompted us to suppose that to achieve high binding affinity to CB₁ receptors and CB₁ over CB₂ selectivity it is important for the tricyclic system to be non-planar. To evaluate the functional profile, several compounds were assayed for the capability to affect gastrointestinal transit in mice, making use of the upper gastrointestinal test which is based on the determination of the intestinal length traveled by a non-absorbable marker as a consequence of the active compound administration. From this test, compound IIAbX was able to induce a dose-dependent gastrointestinal motility increase, as well as compound IIAiX. This effect was markedly reversed by the in vivo administration of CP-55,940, suggesting for the series of 4,5-dihydro-1H-benzo(g)indazole-3-carboxamides antagonistic profile for CB receptors [57].

3.2. 4,5-Dihydro-1H-thieno(2,3-g)indazole-Based Derivatives (VIII) and 4,5-Dihydro-1H-thieno(3,2-g)indazole-Based Derivatives (XI)

A number of compounds sharing a 4,5-dihydro-1H-thieno(2,3-g)indazole scaffold (VIII), which is a homolog of the previously-described 1,4-dihydrothieno(2′,3′-4,5)cyclopenta(1,2-c)pyrazole one (VII) were claimed by Neuroscienze Pharmaness S.C.A.R.L. [59]. The structure of representative compounds and CB₁/CB₂ receptor affinity values are reported in Figure 12. According to binding data, most compounds exhibited a potent and mixed CB₁/CB₂ binding profile, with a proclivity for CB₁ receptors. The thieno(2,3-g)indazole-based derivative VIIIAeX resulted in the most selective for CB₁ receptors between all reported compounds. The disclosed compound VIIIAeX, namely NESS038C6, highlighted CB₁ antagonism behavior by both in isolated organ assays and in vivo tests based on rat intestinal motility (data not shown). Chronic treatment with NESS038C6 in C57BL/6N diet-induced obesity (DIO) mice determined a significant reduction of weight which was comparable to that detected in DIO mice treated with SR141716 [60]. The Neuroscienze Pharmaness S.C.A.R.L. patent [59] encompasses also a series of isomeric compounds incorporating the 4,5-dihydro-1H-thieno(3,2-g)indazole scaffold XI (i.e., XIAbX, Figure 2) and others, but not cannabinoid binding receptor affinity was reported.

Structure of representative 4,5-dihydro-1H-thieno(2,3-g)indazole-based derivatives (VIII). Affinities at CB1 and CB2 receptors were assessed by competition of (3H)-CP 55,940 in mouse cerebellum membranes and in mouse spleen homogenates, respectively [59]. — Figure 12Structure of representative 4,5-dihydro-1H-thieno(2,3-g)indazole-based derivatives (**VIII**). Affinities at CB₁ and CB₂ receptors were assessed by competition of (³H)-CP 55,940 in mouse cerebellum membranes and in mouse spleen homogenates, respectively [59].

3.3. 1,5-Dihydroisothiochromen([4,3-c)pyrazole-Based Derivatives (XIII) and 1,4-Dihydrothiochromeno(4,3-c)pyrazole-Based Derivatives (XIV)

A series of derivatives featuring a 1,5-dihydroisothiochromeno(4,3-c]pyrazole- and 1,4-dihydrothiochromeno(4,3-c)pyrazole-scaffolds, XIII and XIV, respectively (i.e., XIIIBbX or XIVAbX, Figure 2) were claimed by Sanofi-Aventis for cannabinoid receptor interaction, but no biological activity was presented [58].

3.4. 4,5-Dihydro-1H-Pyrazolo(4,3-g)indolizine-Based Derivatives (XVI)

To further extend SAR study on cannabinoid receptors, and driven by the negligible results on CB₁/CB₂ receptor affinity of 1,4-dihydropyrazolo(3,4-a)pyrrolizines (XV), homologue 4,5-dihydro-1H-pyrazolo(4,3-g)indolizines (XVI, Figure 2) have been synthesized [56]. Representative compounds are depicted in Figure 13. According to binding data reported for compounds XVIAbX, XVICbX, XVIDbX with respect to compounds XVAaX, XVAhX, XVIaX, XVIhX, the expansion of the central ring size by a methylene unit led to conformational changes that promote the affinity for CB₁ receptors and improve CB₂/CB₁ selectivity ratio, with XVICbX reaching reasonable affinity for CB₁ receptors (K_i CB₁ = 81 nM) and the highest CB₂/CB₁ selectivity ratio (>12).

Structure of representative 4,5-dihydro-1H-pyrazolo(4,3-g)indolizine-based derivatives (XVI). Affinities at CB1 and CB2 receptors were assessed by competition of (3H)-CP 55,940 in mouse whole-brain membranes and in CHO cell membranes transfected with hCB2 receptors [56]. — Figure 13Structure of representative 4,5-dihydro-1H-pyrazolo(4,3-g)indolizine-based derivatives (**XVI**). Affinities at CB₁ and CB₂ receptors were assessed by competition of (³H)-CP 55,940 in mouse whole-brain membranes and in CHO cell membranes transfected with hCB₂ receptors [56].

4. (5,7)-Condensed Pyrazole Derivatives

4.1. 1,4,5,6-Tetrahydrobenzo(6,7])cyclohepta(1,2-c]pyrazole-Based Derivatives (III)

The intriguing SAR study carried out on ligands with the 1,4-dihydroindeno(1,2-c)pyrazole core (i.e., IAaX, IAhX) endowed with very high binding affinity for CB₂ receptors in comparison to homologous ligands having 4,5-dihydro-1H-benzo(g)indazoles (i.e., IIAbX, IIAiX) exhibiting higher CB₁ binding affinity, prompted us to design and synthetize a new homologous series of general formula III, incorporating 1,4,5,6-tetrahydrobenzo(6,7)cyclohepta(1,2-c)pyrazole scaffold, for cannabinoid receptor interaction [61]. Representative compounds are depicted in Figure 14. Compound IIIAcX, namely NESS0327, was first claimed by Sanofi-Aventis, but no biological data was presented in the patent [58].

Structure of representative 1,4,5,6-tetrahydrobenzo(6,7)cyclohepta(1,2-c)pyrazole-based derivatives (III). Affinities at CB1 and CB2 receptors were assessed by competition of (3H)-CP 55,940 in mouse whole-brain membranes and in CHO cell membranes transfected with hCB2 receptors [61]. — Figure 14Structure of representative 1,4,5,6-tetrahydrobenzo(6,7)cyclohepta(1,2-c)pyrazole-based derivatives (**III**). Affinities at CB₁ and CB₂ receptors were assessed by competition of (³H)-CP 55,940 in mouse whole-brain membranes and in CHO cell membranes transfected with hCB₂ receptors [61].

In general, all the investigated compounds exhibited preferential affinity for CB₁ receptors, with NESS0327, endowed of K_i CB₁ = 4.2 nM, K_i CB₂ = 55.7 nM and K_i CB₂/K_i CB₁ selectivity ratio = 13.26. Slightly different values for CB₁ receptors, possibly due to different receptor matrix, were reported for IIIAcX by two other independent groups: Stoit et al. K_i CB₁ = 126 nM [62] and Zhang et al. 18.4 nM [63] using (³H)-CP 55,940 and hCB₁ receptor cloned in CHO cells or membranes isolated from a HEK-293 expression system, respectively. Compound IIIIcX, bearing the bulky myrtanil substituent, showed the best CB₁ receptor affinity which was equivalent to that exhibited by IIIAcX. Moving the chlorine atom from position 8 to 9 of the myrtanil-based derivative IIIIcX to give IIIIdX induced a decrease of CB₁ receptor affinity with a concurrent loss of selectivity. CB₁ receptor intrinsic activity of selected derivatives was evaluated through in vitro tests based on the determination of phosphorylated ERK 1/2 (P-ERK 1/2) expression in mouse neuroblastoma N1E-115 cell line. According to rimonabant, compounds IIIAcX and IIIBcX didn’t affect P-ERK expression in N1E-115 cells in the concentration range 1 nM-10µM; P-ERK 1/2 (% of vehicle): vehicle, 100 ÷ 10; rimonabant (1 µM): 110 ÷ 8; IIIAcX (1 µM): 111 ÷ 12; IIIBcX (1 µM): 95 ÷ 9. Furthermore, these compounds inhibited the P-ERK 1/2 expression up-regulation induced by the reference cannabinoid agonist WIN-55,212-2; vehicle: 185 ÷ 12; rimonabant (1 µM): 108 ÷ 7; IIIAcX (1 µM): 115 ÷ 13; IIIBcX (1 µM): 103 ÷ 9. In contrast, the myrtanil-based derivatives IIIIcX and IIIIdX enhanced P-ERK 1/2 expression in N1E-115 cells, highlighting CB₁ receptor agonism profile for both compounds [61]. The pharmacological relevance of 1,4,5,6-tetrahydrobenzo(6,7)cyclohepta(1,2-c)pyrazole-based derivatives III emerged from the ability of antagonist NESS0327 to induce reduction of weight gain and food intake equivalent to that of rimonabant [64]. Furthermore, it was reported that the neutral antagonist profile exhibited by NESS0327 appeared important to avoid the side effects induced by rimonabant administration (i.e., suppression of the constitutive CB₁ receptor activity in the ventral tegmental area and basolateral amygdala causing anxiety and reduced motivation for reward). Several patents testify to the pharmaceutical interest of NESS0327 [65,66,67,68]. Within this frame, the University of Queensland claimed method and agents for reducing general anesthetic induced neuroexcitation, attributing such side effect especially to neurosteroid general anesthetic agents as alfaxalone, even if the patent covers all general anesthetics in use [69]. In vitro electrophysiological analysis showed alfaxalone significantly decreased the amplitude of inhibitory synaptic currents (IPSC) on hypoglossal motor neurons, at a concentration ranging between 100 nM to 10 µM, consistent with increased in vivo motor activity and muscle twitching induced by alfaxalone. Treatment of hypoglossal motor neurons with NESS0327 was demonstrated to attenuate the effect of alfaxalone both on evoked than spontaneous IPSC amplitude. In vivo analysis conducted on Wistar rats highlighted administration of NESS0327 as a premedication prior to alfaxalone anesthesia significantly reduced muscle twitching during the induction and recovery phases of anesthesia. More importantly, premedication with NESS0327 had no detrimental effect on arterial O₂ saturation or respiration rate during alfaxalone anesthesia [69].

4.2. 4,5-Dihydro-1H-benzo(2,3)oxepino(4,5-c)pyrazole-Based Derivatives (VI)

Endocannabinoids are orexigenic factors promoting appetite via CB₁ receptor activation. This finding provided the rationale for the development of CB₁ antagonist/inverse agonist rimonabant for obesity treatment and its metabolic complications. However, rimonabant side effects responsible for its withdrawal were principally related to both activities on SNC and to inverse agonism profile [70,71]. Therefore, new strategies have been proposed for the development of more safe anti-obesity agents, such as the identification of peripherally restricted CB₁ receptor antagonists [71] as well as neutral CB₁ receptor antagonists or CB₁ allosteric modulators [72]. Within this frame, it was envisioned that bioisosteric modification of 1,4,5,6-tetrahydrobenzo(6,7)cyclohepta(1,2-c)pyrazole core (III) might offer new templates for CB₁ receptor interaction. Thus, a series of 4,5-dihydro-1H-benzo(2,3)oxepino(4,5-c)pyrazoles (VI, Figure 2), containing an oxygen atom at position 6 in place of a methylene unit, were designed and synthesized. Such bioisosteric methylene/oxygen replacement might give access to CB₁ ligands with increased polar surface area and decreased lipophilicity, which were considered critical parameters to influence the blood-brain permeability. Representative compounds are VIAcX, VIDcX, VIIcX (Figure 15), all exhibiting nanomolar/near nanomolar affinity for CB₁ receptors [73]. Within this frame, a series of compounds sharing a 4,5-dihydro-1H-benzo(2,3)oxepino(4,5-c)pyrazole core, including VIAcX, were claimed by Cadila Healthcare Limited, but no binding data for cannabinoid receptors were presented [74]. However, the compounds of the invention were generally said, in the cAMP accumulation model, to antagonizes the WIN-55,212-2 inhibition of forskolin-induced cAMP accumulation in hCB₁ CHO cells. Furthermore, VIAcX, and other representative compounds have been shown to reduce, in the sucrose solution intake rat model, the sucrose solution consumption [74,75]. In our hands, compound VIAcX, namely NESS06SM, emerged for its nanomolar CB₁ receptor affinity and good selectivity with respect to CB₂ one (K_i CB₁ = 10.25 nM, K_i CB₂ > 5000 nM). Evaluation of intrinsic activity carried out on NESS06SM highlighted a neutral antagonist profile both in (³⁵S)GTPγS assay and in isolated organ assays (mouse vas deferens) [76]. In silico parameters (cLogP_OW, tPSA, log BB), compared with IIIAcX (NESS0327) and other already known CB₁ antagonists (i.e., rimonabant), suggested that NESS06SM exhibited sparing BBB permeability. Moreover, chronic treatment with NESS06SM resulted in the reduction of body weight and cardiovascular risk factor improvement in C57BL/6N diet-induced obesity (DIO) mice fed with a fat diet. Furthermore, in contrast to rimonabant, the chronic treatment of NESS06SM did not change mRNA expression of both monoaminergic transporter and neurotrophins, highly related to anxiety and mood disorders [76]. Interestingly, the co-treatment of NESS06SM has been shown to reduce food intake and weight gain, mitigate the side effects induced by chronic administration of the atypical antipsychotic olanzapine, without altering the positive effects of olanzapine on behavior [77].

Structure of representative 4,5-dihydro-1H-benzo(2,3)oxepino(4,5-c)pyrazole-based derivatives (VI). Affinities at CB1 and CB2 receptors were assessed by competition of (3H)-CP 55,940 in mouse cerebellum membranes and in mouse spleen homogenates, respectively [73]. — Figure 15Structure of representative 4,5-dihydro-1H-benzo(2,3)oxepino(4,5-c)pyrazole-based derivatives (VI). Affinities at CB₁ and CB₂ receptors were assessed by competition of (³H)-CP 55,940 in mouse cerebellum membranes and in mouse spleen homogenates, respectively [73].

As expected, evaluation of the intrinsic activity of VIDcX, namely SM-11, evidenced CB₁ antagonist activity, both in in vitro test (P-ERK 1/2 expression in N1E-115 cells) and in isolated organs (mouse vas deferens). Behavioral studies highlighted that dose-dependently SM-11 decreased food intake in rats by 15–20%. Moreover, the i.v. administration of SM-11 fully and readily antagonized the effect of the agonist WIN-55,212-2 on the activity of ventral tegmental area (VTA) dopamine neurons projecting to the nucleus accumbens cells, confirming its antagonist profile. Furthermore, this data supported that SM-11 can lessen the hedonic aspect of food thus promoting bodyweight reduction [78].

4.3. 1,4,5,6-Tetrahydrothieno(2′,3′-6,7])cyclohepta(1,2-c)pyrazole-Based Derivatives (IX) and 1,4,5,6-Tetrahydrothieno(3′,2′-6,7)cyclohepta(1,2-c)pyrazole-Based Derivatives (XII)

A series of derivatives incorporating a 1,4,5,6-tetrahydrothieno(2′,3′-6,7)cyclohepta(1,2-c)pyrazole- and 1,4,5,6-tetrahydrothieno(3′,2′-6,7)cyclohepta(1,2-c)pyrazole-scaffolds IX and XII, respectively, (i.e., IXAcX or XIIAcX, Figure 2) were claimed by Neuroscienze Pharmaness S.C.A.R.L. for cannabinoid receptor interaction, but no biological activity was presented [59].

4.4. 1,4,5,6-Tetrahydropyrazolo(3,4-c)pyrrolo(1,2-a)azepine-Based Derivatives (XVII)

A series of 1,4,5,6-tetrahydropyrazolo(3,4-c)pyrrolo(1,2-a)azepine-based derivatives (XVII, Figure 2) has been investigated for cannabinoid receptor interaction [56]. Representative compounds are depicted in Figure 16, all devoid of affinity for CB₂ receptors and endowed of negligible affinity for CB₁ receptors.

Structure of representative 1,4,5,6-tetrahydropyrazolo(3,4-c)pyrrolo(1,2-a)azepine-based derivatives (XVII). Affinities at CB1 and CB2 receptors were assessed by competition of (3H)-CP 55,940 in mouse whole-brain membranes and in CHO cell membranes transfected with hCB2 receptors [56]. — Figure 16Structure of representative 1,4,5,6-tetrahydropyrazolo(3,4-c)pyrrolo(1,2-a)azepine-based derivatives (**XVII**). Affinities at CB₁ and CB₂ receptors were assessed by competition of (³H)-CP 55,940 in mouse whole-brain membranes and in CHO cell membranes transfected with hCB₂ receptors [56].

5. (5,8)-Condensed Pyrazole Derivatives

4,5,6,7-Tetrahydro-1H-benzo(7,8)cyclooct(1,2-c)pyrazole-Based Derivatives (IV)

Zhang et al. described the synthesis and biological evaluation of a series of conformationally constrained analogs of rimonabant [63]. Within this frame, they synthesized both compound IIIAcX from our lab and IVAdX (Figure 17) which is the only pyrazole-based tricyclic compound known belonging to (5,8)-condensed derivatives, featuring the 4,5,6,7-tetrahydro-1H-benzo(7,8)cycloocta(1,2-c)pyrazole core. The compound, endowed of lower affinity for CB₂ than CB₁ receptors, exhibited a similar trend with respect to homologous compounds IIAbX and IIIAcX. However, increasing the carbocyclic central ring size by one methylene unit, i.e., from (5,7)- to (5,8)-condensed pyrazole derivatives, involved a marked loss of affinity for CB₁ receptors.

Structure of 4,5,6,7-tetrahydro-1H-benzo(7,8])cycloocta(1,2-c)pyrazole derivative IVAdX. Affinities at CB1 and CB2 receptors were assessed by competition of (3H)-CP 55,940 in HEK-293 and CHO-K1 cell membranes, respectively [63]. — Figure 17Structure of 4,5,6,7-tetrahydro-1H-benzo(7,8])cycloocta(1,2-c)pyrazole derivative **IVAdX**. Affinities at CB₁ and CB₂ receptors were assessed by competition of (³H)-CP 55,940 in HEK-293 and CHO-K1 cell membranes, respectively [63].

6. Miscellaneous Derivatives

Other pyrazole-based tricyclic derivatives, featuring the pyrazolo(5,1-f)(1,6)naphthyridine core (Figure 18), were investigated for cannabinoid receptor interaction [79].

Structure of representative pyrazolo(5,1-f)(1,6)naphthyridine-based derivatives (5–7). Affinities at CB1 and CB2 receptors were assessed by competition of (3H)-CP 55,940 in transfected human CB1 and CB2 CHO cells [79]. — Figure 18Structure of representative pyrazolo(5,1-f)(1,6)naphthyridine-based derivatives (5–7). Affinities at CB₁ and CB₂ receptors were assessed by competition of (³H)-CP 55,940 in transfected human CB₁ and CB₂ CHO cells [79].

The pyrazolo(5,1-f)(1,6)naphthyridine derivatives were synthesized making use of AgOTf and proline-cocatalyzed multicomponent methodology (Scheme 2), starting from the appropriate o-alkynylaldehydes 9, p-toluenesulfonyl hydrazide (PTSH) and ethyl pyruvate, to gave key pyrazole-esters 10 which, hydrolyzed with NaOH, afforded the corresponding acids 11. Target compounds were synthesized by condensation of acids 11, previously activated with pivaloyl chloride, with the appropriate amines. The o-alkynylaldehydes 9 were obtained from 2-bromonicotinaldehyde 8 and appropriate alkynes which were reacted under the conventional Sonogashira conditions.

General synthetic route for the preparation of pyrazolo(5,1-f)(1,6)naphthyridine derivatives 5–7. — Scheme 2General synthetic route for the preparation of pyrazolo(5,1-f)(1,6)naphthyridine derivatives **5–7**.

Compounds 5–7 exhibited affinity levels for CB₂ receptors in the near nM range (K_i: 33–67 nM) with a good degree of selectivity for CB₂ receptors compared to CB₁. According to in vitro assays based on the effects of forskolin-stimulated cAMP levels in human CB₂ CHO cells, compounds 5–7 exhibited antagonist/inverse agonist properties [79].

7. Conclusions

In the last decades, the CB₁ antagonist/inverse agonist rimonabant has been considered an extremely valuable lead for the design of new ligands for CB receptors interaction, with potential therapeutic value. In the context of this review, the introduction of structural constraints in rimonabant, the use of medicinal chemistry approaches as homologation or bioisosterism, gave access to several compounds most of which belong to (5,5), (5,6) and (5,7)-condensed tricyclic pyrazole derivatives. Here we have summarized the extensive SAR studies carried out on such compounds, allowing us to identify different ligands endowed with high affinity and selectivity for CB₁ or CB₂ receptors. In particular, the pharmacological relevance of 1,4-dihydroindeno(1,2-c)pyrazole-based I compounds, belonging to (5,5) tricyclic pyrazole derivatives, emerged from the significant anti-nociceptive activity of the potent and selective CB₂ agonist IDhX, by alleviating both mechanical allodynia and thermal hyperalgesia in Spared Nerve Injury (SNI) neuropathic mice. The interest of ligands belonging to (5,5) tricyclic pyrazole derivatives emerged also for their potential as anti-glaucoma agents, for the ability to reduce intraocular pressure (IOP). Compound XIhZ, featuring the 1,4-dihydrothieno(3′,2′-4,5)cyclopenta(1,2-c)pyrazole core and exhibiting high and mixed CB₁/CB₂ receptor affinities, effectively reduced intraocular pressure in the animal model of old DBA/2J mice, providing a potential alternative to the use of WIN-55,212-2 and smoking marijuana, known for their IOP lowering properties. SAR study pointed out the relevance of ligands belonging to (5,7) tricyclic pyrazole derivatives, for their anti-obesity potential. In this frame, the selective CB₁ ligand VIAcX, featuring the 4,5-dihydro-1H-benzo(2,3)oxepino(4,5-c)pyrazole core, exhibiting neutral antagonist profile, effectively reduced body weight with the improvement of cardiovascular risk factor in C57BL/6N diet-induced obesity (DIO) mice fed with fat diet. Preliminary data evidenced the potentiality of compound VIAcX in the treatment of obesity with a more safe profile with respect to the antagonist/inverse agonist rimonabant.

Author Contributions

Conceptualization, B.A., and G.A.P.; methodology, G.M.; resources, P.C. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Università degli Studi di Sassari: fondo di Ateneo per la ricerca 2019, 2020.

Conflicts of Interest

The authors declare no conflict of interest.

Footnotes

Footnote Group

References

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References

1.Lambert D.M., Fowler C.J. The Endocannabinoid System: Drug Targets, Lead Compounds, and Potential Therapeutic Applications. J. Med. Chem. 2005;36:5059–5087. doi: 10.1021/jm058183t.
2.Pertwee R., editor. Cannabinoids. Springler; Berlin/Heidelberg, Germany: 2005.
3.Pop E. Cannabinoids, endogenous ligands and synthetic analogs. Curr. Opin. Chem. Biol. 1999;3:418–425. doi: 10.1016/S1367-5931(99)80062-3.
4.Matsuda L.A., Lolait S.J., Brownstein M.J., Young A.C., Bonner T.I. Structure of a cannabinoid receptor and functional expression of the cloned cDNA. Nature. 1990;346:561–564. doi: 10.1038/346561a0.
5.Munro S., Thomas K.L., Abu-Shaar M. Molecular characterization of a peripheral receptor for cannabinoids. Nat. Cell Biol. 1993;365:61–65. doi: 10.1038/365061a0.
6.Herkenham M., Lynn A.B., Little M.D., Johnson M.R., Melvin L.S., de Costa B.R., Rice K.C. Cannabinoid receptor location in brain. Proc. Natl. Acad. Sci. USA. 1990;87:1932–1936. doi: 10.1073/pnas.87.5.1932.
7.Howlet A.C. The CB1 cannabinoid receptor in the brain. Neurobiol. Dis. 1998;5:405–416. doi: 10.1006/nbdi.1998.0215.
8.Casu M.A., Porcella A., Ruiu S., Saba P., Marchese G., Carai M.A.M., Reali R., Gessa G.L., Pani L. Differential distribution of functional cannabinoid CB1 receptors in the mouse gastroenteric tract. Eur. J. Pharmacol. 2003;459:97–105. doi: 10.1016/S0014-2999(02)02830-3.
9.Glass M. The role of Cannabinoids in neurodegenerative diseases. Prog. Neuro-Psychopharmacol. Biol. Psychiatry. 2001;25:743–765. doi: 10.1016/S0278-5846(01)00162-2.
10.Porcella A., Casellas P., Gessa G.L., Pani L. Cannabinoid receptor CB1 mRNA is highly expressed in the rat ciliary body: Implications for the antiglaucoma properties of marihuana. Mol. Brain Res. 1998;58:240–245. doi: 10.1016/S0169-328X(98)00105-3.
11.Galiegue S., Mary S., Marchand J., Dussossoy D., Carriere D., Carayon P., Bouaboula M., Shire D., Fur G., Casellas P. Expression of Central and Peripheral Cannabinoid Receptors in Human Immune Tissues and Leukocyte Subpopulations. Eur. J. Biochem. 1995;232:54–61. doi: 10.1111/j.1432-1033.1995.tb20780.x.
12.Gong J.-P., Onaivi E.S., Ishiguro H., Liu Q.-R., Tagliaferro P.A., Brusco A., Uhl G.R. Cannabinoid CB2 receptors: Immunohistochemical localization in rat brain. Brain Res. 2006;1071:10–23. doi: 10.1016/j.brainres.2005.11.035.
13.Lu Q., Straiker A., Lu Q., Maguire G. Expression of CB2 cannabinoid receptor mRNA in adult rat retina. Vis. Neurosci. 2000;17:91–95. doi: 10.1017/S0952523800171093.
14.Murineddu G., Asproni B., Pinna G.A. A Survey of Recent Patents on CB2 Agonists in the Management of Pain. Recent Pat. Cns Drug Discov. 2012;7:4–24. doi: 10.2174/157488912798842214.
15.Marino S., Idris A.I. Emerging therapeutic targets in cancer induced bone disease: A focus on the peripheral type 2 cannabinoid receptor. Pharmacol. Res. 2017;119:391–403. doi: 10.1016/j.phrs.2017.02.023.
16.Morales P., Blasco-Benito S., Andradas C., Gómez-Cañas M., Flores J.M., Goya P., Fernández-Ruiz J., Sánchez C., Jagerovic N. Selective, nontoxic CB2 cannabinoid o-quinone with in vivo activity against triple-negative breast cancer. J. Med. Chem. 2015;58:2256–2264. doi: 10.1021/acs.jmedchem.5b00078.
17.Yang P., Wang L., Feng R., Almehizia A.A., Tong Q., Myint K.-Z., Ouyang Q., Alqarni M.H., Wang L., Xie X.-Q. Novel triaryl sulphonamide derivatives as selective cannabinoid receptor 2 inverse agonists and osteoclast inhibitors: Discovery, optimization, and biological evaluation. J. Med. Chem. 2013;56:2045–2058. doi: 10.1021/jm3017464.
18.Pertwee R.G. Emerging strategies for exploiting cannabinoid receptor agonists as medicines. Br. J. Pharmacol. 2009;156:397–411. doi: 10.1111/j.1476-5381.2008.00048.x.
19.Mainolfi N., Powers J., Amin J., Long D., Lee W., McLaughlin M.-E., Jaffee B., Brain C., Elliott J., Sivak J.M. An effective prodrug strategy to selectively enhance ocular exposure of a cannabinoid receptor (CB1/2) agonist. J. Med. Chem. 2013;56:5464–5472. doi: 10.1021/jm4004939.
20.Pi-Sunyer F.X., Aronne L.J., Heshmati H.M., Devin J., Rosenstock J., for the RIO-North America Study Group Effect of Rimonabant, a Cannabinoid-1 Receptor Blocker, on Weight and Cardiometabolic Risk Factors in Overweight or Obese Patients. JAMA. 2006;295:761–775. doi: 10.1001/jama.295.7.761.
21.Zhang Y., Seltzman H.-H., Brackeen M., Thomas B.-F. Structure-Activity Relationships and Conformational Freedom of CB1 Receptor Antagonists and Inverse Agonists. In: Reggio P.H., editor. The Cannabinoid Receptors. 1st ed. Humana Press; New York, NY, USA: 2009. pp. 95–119.
22.Chang C.-P., Wu C.-H., Song J.-S., Chou M.-C., Wong Y.-C., Lin Y., Yeh T.-K., Sadani A.A., Ou M.-H., Chen K.-H., et al. Discovery of 1-(2,4-dichlorophenyl)-N-(piperidin-1-yl)-4-((pyrrolidine-1-sulfonamido)methyl)-5-(5-((4-(trifluoromethyl) phenyl)ethynyl)thiophene-2-yl)-1H-pyrazole-3-carboxamide as a novel peripherally restricted cannabinoid-1 receptor antagonist with significant weight-loss efficacy in diet-induced obese mice. J. Med. Chem. 2013;56:9920–9933. doi: 10.1021/jm401158e.
23.Mussinu J.-M., Ruiu S., Mulè A., Pau A., Carai M.A.M., Loriga G., Murineddu G., Pinna G.A. Tricyclic pyrazoles. Part 1: Synthesis and biological evaluation of novel 1,4-dihydroindeno(1,2-c)pyrazol-based ligands for CB1 and CB2 cannabinoid receptors. Bioorg. Med. Chem. 2003;11:251–263. doi: 10.1016/S0968-0896(02)00319-X.
24.Murineddu G., Lazzari P., Ruiu S., Sanna A., Loriga G., Manca I., Falzoi M., Dessì C., Curzu M.M., Chelucci G., et al. pyrazoles. 4. Synthesis and biological evaluation of analogues of the robust and selective CB2 cannabinoid ligand 1-(2′,4′-dichlorophenyl)-6-methyl-N-piperidin-1-yl-1,4-dihydroindeno(1,2-c)pyrazole-3-carboxamide. J. Med. Chem. 2006;49:7502–7512. doi: 10.1021/jm060920d.
25.Han S., Thatte J., Buzard D.J., Jones R.M. Therapeutic Utility of Cannabinoid Receptor Type 2 (CB2) Selective Agonists. J. Med. Chem. 2013;56:8224–8256. doi: 10.1021/jm4005626.
26.Murineddu G., Asproni B., Ruiu S., Deligia F., Falzoi M., Pau A., Thomas B.F., Zhang Y., Pinna G.A., Pani L., et al. Tricyclic pyrazoles. Part 5. Novel 1,4-dihydroindeno(1,2-c)pyrazolo CB2 ligands using molecular hybridization based on scaffold hopping. Open Med. Chem. J. 2012;6:1–14. doi: 10.2174/1874104501206010001.
27.Kotsikorou E., Navas F., III, Roche M.J., Gilliam A.F., Thomas B.F., Seltzman H.H., Kumar P., Song Z.-H., Hurst D.P., Lynch D.L., et al. The importance of hydrogen bonding and aromatic stacking to the affinity and efficacy of cannabinoid receptor CB2 antagonist 5-(4-chloro-3-methylphenyl)-1-((4-methylphenyl)methyl)-N-((1S,2S,4R)-1,3,3-trimethylbicyclo(2.2.1)hept-2-yl)-1H-pyrazole-3-carboxamide (SR144528) J. Med. Chem. 2013;56:6593–6612. doi: 10.1021/jm400070u.
28.Barth F., Millan J., Oustric D., Rinaldi M., Vernhet M. 1-Benzylpyrazole-3-carboxylic acid tricyclic derivatives as cannabinoid receptor antagonists. US6916838B1. U.S. Pantent. 2005 Jul 12;
29.Deiana V., Gómez-Cañas M., Pazos M.R., Fernández-Ruiz J., Asproni B., Cichero E., Fossa P., Muñoz E., Deligia F., Murineddu G., et al. Tricyclic pyrazoles. Part 8. Synthesis, biological evaluation and modelling of tricyclic pyrazole carboxamides as potential CB2 receptor ligands with antagonist/inverse agonist properties. Eur. J. Med. Chem. 2016;112:66–80. doi: 10.1016/j.ejmech.2016.02.005.
30.Soethoudt M., Grether U., Fingerle J., Grim T.W., Fezza F., de Petrocellis L., Ullmer C., Rothenhäusler B., Perret C., van Gils N., et al. Cannabinoid CB2 receptor ligand profiling reveals biased signalling and off-target activity. Nat. Commun. 2017;8:13958. doi: 10.1038/ncomms13958.
31.Klein T.W., Newton C., Patterson C., Agudelo M. Methods and compositions for reducing serum levels of immunoglobulin E (IgE) WO2013/033155A1. 2013 Mar 7;
32.Li S.-S., Wang L.-L., Liu M., Jiang S.-K., Zhang M., Tian Z.-L., Wang M., Li J.-Y., Zhao R., Guan D.-W. Cannabinoid CB2 receptors are involved in the regulation of fibrogenesis during skin wound repair in mice. Mol. Med. Rep. 2016;13:3441–3450. doi: 10.3892/mmr.2016.4961.
33.Naschi M., Hajikhani M., Ebrahimi G.M., Zarrindast M.-R. Interaction between NMDA and CB2 function in the dorsal hippocampus on memory consolidation impairment: An isobologram analysis. Psychopharmacology. 2017;234:507–514. doi: 10.1007/s00213-016-4481-9.
34.Xia K.-K., Shen J.-X., Huang Z.-B., Song H.-M., Gao M., Chen D.-J., Zhang S.-J., Wu J. Heterogeneity of cannabinoid ligand-induced modulations in intracellular Ca2+ signals of mouse pancreatic acinar cells in vitro. Acta Pharmacol. Sinica. 2019;40:410–417. doi: 10.1038/s41401-018-0074-y.
35.McBrinn R.C., Fraser J., Hope A.G., Gray D.W., Barratt C.L.R., da Silva S.J.M., Brown S.G. Novel pharmacological actions of trequinsin hydrochloride improve human sperm cell motility and function. Br. J. Pharmacol. 2019;176:4521–4536. doi: 10.1111/bph.14814.
36.Khakpai F., Ebrahimi-Ghiri M., Alijanpour S., Zarrindast M.-R. Ketamine-induced antidepressant like effects in mice: A possible involvement of cannabinoid system. Biomed. Pharmacother. 2019;112:108717. doi: 10.1016/j.biopha.2019.108717.
37.Luongo L., Palazzo E., Tambaro S., Giordano C., Gatta L., Scafuro M., Rossi F., Lazzari P., Pani L., De Novellis V., et al. 1-(2′,4′-dichlorophenyl)-6-methyl-N-cyclohexylamine-1,4-dihydroindeno(1,2-c)pyrazole-3-carboxamide, a novel CB2 agonist, alleviates neuropathic pain through functional microglial changes in mice. Neurobiol. Dis. 2010;37:177–185. doi: 10.1016/j.nbd.2009.09.021.
38.Pinna G., Loriga G., Lazzari P., Ruiu S., Falzoi M., Frau S., Pau A., Murineddu G., Asproni B., Pinna G.A. Tricyclic pyrazoles. Part 6. Benzofuro(3,2-c)pyrazoles: A versatile architecture for CB2 selective ligands. Eur. J. Med. Chem. 2014;82:281–292. doi: 10.1016/j.ejmech.2014.05.055.
39.Lazzari P., Loriga G., Manca I., Pinna G.A. Tricyclic pyrazole derivatives and microemulsions thereof as CB1- and/or CB2-inhibitors. EP2223913A1. 2010 Sep 1;
40.Pinna G., Curzu M.M., Dore A., Lazzari P., Ruiu S., Pau A., Murineddu G., Pinna G.A. Tricyclic pyrazoles part 7. Discovery of potent and selective dihydrothienocyclopentapyrazole derived CB2 ligands. Eur. J. Med. Chem. 2014;85:747–757. doi: 10.1016/j.ejmech.2014.08.042.
41.Lazzari P., Loriga G., Manca I., Pinna G.A. Pharmaceutical compounds. US2010/0215759A1. U.S. Patent. 2010 Aug 26;
42.Pertwee R.G., Stevenson L.A., Elrick D.B., Mechoulam R., Corbett A.D. Inhibitory effects of certain enantiomeric cannabinoids in the mouse vas deferens and the myenteric plexus preparation of guinea-pig small intestine. Br. J. Pharmacol. 1992;105:980–984. doi: 10.1111/j.1476-5381.1992.tb09088.x.
43.Heijl A., Leske M.C., Bengtsson B., Hyman L., Hussein M. Reduction of intraocular pressure and glaucoma progression: Results from the Early Manifest Glaucoma Trial. Arch. Ophthalmol. 2002;120:1268–1279. doi: 10.1001/archopht.120.10.1268.
44.Hepler R.S., Frank I.R. Marihuana smoking and intraocular pressure. JAMA. 1971;217:1392. doi: 10.1001/jama.1971.03190100074024.
45.Allen R.C., Sheppard J.D., III, Lattanzio F., Jr., Lichtman A., Crouch E., Jr., Williams P. Ocular and systemic effects of WIN-55,212-2 in normotensive rabbits. Investig. Ophthalmol. Vis. Sci. 2003;44:4423.
46.Hosseini A., Lattanzio F.A., Williams P.B., Tibbs D., Samudre S.S., Allen R.C. Chronic topical administration of WIN-55,212-2 maintains a reduction in IOP in a rat glaucoma model without adverse effects. Exp. Eye Res. 2006;82:753–759. doi: 10.1016/j.exer.2005.09.017.
47.Porcella A., Maxia C., Gessa G.L., Pani L. The synthetic cannabinoid WIN55212-2 decreases the intraocular pressure in human glaucoma resistant to conventional therapies. Eur. J. Neurosci. 2001;13:409–412. doi: 10.1046/j.0953-816X.2000.01401.x.
48.Zhong L., Geng L., Njie Y., Feng W., Song Z.-H. CB2 Cannabinoid Receptors in Trabecular Meshwork Cells Mediate JWH015-Induced Enhancement of Aqueous Humor Outflow Facility. Investig. Opthalmol. Vis. Sci. 2005;46:1988–1992. doi: 10.1167/iovs.04-0651.
49.Aymerich M.S., Aso E., Abellanas M.A., Tolon R.M., Ramos J.A., Ferrer I., Romero J., Fernández-Ruiz J. Cannabinoid pharmacology/therapeutics in chronic degenerative disorders affecting the central nervous system. Biochem. Pharmacol. 2018;157:67–84. doi: 10.1016/j.bcp.2018.08.016.
50.Yazulla S. Endocannabinoids in the retina: From marijuana to neuroprotection. Prog. Retin. Eye Res. 2008;27:501–526. doi: 10.1016/j.preteyeres.2008.07.002.
51.Pietrucha-Dutczak M., Amadio M., Govoni S., Lewin-Kowalik J., Smedowski A. The role of endogenous neuroprotective mechanisms in the prevention of retinal ganglion cells degeneration. Front. Neurosci. 2018;12:1–23. doi: 10.3389/fnins.2018.00834.
52.Tomida I., Pertwee R.G., Azuara-Blanco A. Cannabinoids and glaucoma. Br. J. Ophthalmol. 2004;88:708–713. doi: 10.1136/bjo.2003.032250.
53.Novack G.D. Cannabinoids for treatment of glaucoma. Curr. Opin. Ophthalmol. 2016;27:146–150. doi: 10.1097/ICU.0000000000000242.
54.Panahi Y., Manayi A., Nikan M., Vazirian M. The arguments for and against cannabinoids application in glaucomatous retinopathy. Biomed. Pharmacother. 2017;86:620–627. doi: 10.1016/j.biopha.2016.11.106.
55.Allingham R.R. Shield’s Textbook of Glaucoma. Lippincott Williams & Wilkins; Philadelphia, PA, USA: 2011. pp. 390–399.
56.Asproni B., Manca I., Pinna G., Cichero E., Fossa P., Murineddu G., Lazzari P., Loriga G., Pinna G.A. Novel pyrrolocycloalkylpyrazole analogues as CB1 ligands. Chem. Biol. Drug Des. 2018;91:181–193. doi: 10.1111/cbdd.13069.
57.Murineddu G., Ruiu S., Mussinu J.-M., Loriga G., Grella G.E., Carai M.A.M., Lazzari P., Pani L., Pinna G.A. Tricyclic pyrazoles. Part 2: Synthesis and biological evaluation of novel 4,5-dihydro-1H-benzo(g)indazole-based ligands for cannabinoid receptors. Bioorg. Med. Chem. 2005;13:3309–3320. doi: 10.1016/j.bmc.2005.02.032.
58.Barth F., Congy C., Martinez S., Rinaldi M. Pyrazolecarboxylic acid tricyclic derivatives, preparation and pharmaceutical compositions containing same. US2005/192332A1. U.S. Patent. 2005 Sep 1;
59.Lazzari P., Ruiu S., Pinna G.A., Murineddu G. Pharmaceutical compounds. US7485730B2. U.S. Patent. 2009 Feb 3;
60.Mastinu A., Pira M., Pani L., Pinna G.A., Lazzari P. NESS038C6, a novel selective CB1 antagonist agent with anti-obesity activity and improved molecular profile. Behav. Brain Res. 2012;234:192–204. doi: 10.1016/j.bbr.2012.06.033.
61.Lazzari P., Distinto R., Manca I., Baillie G., Murineddu G., Pira M., Falzoi M., Sani M., Morales P., Ross R., et al. A critical review of both the synthesis approach and the receptor profile of the 8-chloro-1-(2′,4′-dichlorophenyl)-N-piperidin-1-yl-1,4,5,6-tetrahydrobenzo(6,7)cyclohepta(1,2-c)pyrazole-3-carboxamide and analogue derivatives. Eur. J. Med. Chem. 2016;121:194–208. doi: 10.1016/j.ejmech.2016.05.011.
62.Stoit A.R., Lange J.H.M., Hartog A.P.D., Ronken E., Tipker K., van Stuivenberg H.H., Dijksman J.A.R., Wals H.C., Kruse C.G. Design, Synthesis and Biological Activity of Rigid Cannabinoid CB1 Receptor Antagonists. Chem. Pharm. Bull. 2002;50:1109–1113. doi: 10.1248/cpb.50.1109.
63.Zhang Y., Burgess J.P., Brackeen M., Gilliam A., Mascarella S.W., Page K., Seltzman H.H., Thomas B.F. Conformationally constrained analogues of N-(piperidinyl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (SR141716): Design, synthesis, computational analysis, and biological evaluations. J. Med. Chem. 2008;51:3526–3539. doi: 10.1021/jm8000778.
64.Meye F.J., Trezza V., Vanderschuren L.J.M.J., Ramakers G.M.J., Adan R.A.H. Neutral antagonism at the cannabinoid 1 receptor: A safer treatment for obesity. Mol. Psyc. 2013;18:1294–1301. doi: 10.1038/mp.2012.145.
65.Lange J.H.M., Kruse C.G., Shadid B. Compounds with a Combination of Cannabinoids-CB1 Antagonism and Acetylcholinesterase Inhibition. US2008/0153867A1. U.S. Patent. 2008 Jun 26;
66.Antel J., Gregory P.-C., Lange J.H.M., Firnges M., Reiche D. Pharmaceutical Compositions Comprising CBX Cannabinoid Receptor Modulators and Potassium Channel Modulators. US2007/0254862A1. U.S. Patent. 2007 Nov 1;
67.Firnges M., Gregory P.-C., Antel J., Lange J.H.M., Waldeck H. Pharmaceutical Compositions Comprising CB1 Cannabinoid Receptor Antagonists and Potassium Channel Openers for the Treatment of Obesity and Related Conditions. US2006/0128673A1. U.S. Patent. 2006 Jun 15;
68.Ralston S.H., Greig I.R., Ross R.A., Mohamed A.I.I., Van’t Hof R.J. Cannabinoid Receptor Inverse Agonists and Neutral Antagonists as Therapeutic Agents for the Treatment Of Bone Disorders. WO2004/078261A1. 2004 Sep 16;
69.Bellingham M. Method and agents for reducing general anaesthetic induced neuroexcitation. WO2018/094470A1. 2018 May 31;
70.Jones D. End of the line for cannabinoid receptor 1 as an anti-obesity target? Nat. Rev. Drug Discov. 2008;7:961–962. doi: 10.1038/nrd2775.
71.Cinar R., Iyer M.R., Kunos G. The therapeutic potential of second and third generation CB1R antagonists. Pharmacol. Ther. 2020;208:107477. doi: 10.1016/j.pharmthera.2020.107477.
72.Nguyen T., Thomas B.F., Zhang Y. Overcoming the Psychiatric Side Effects of the Cannabinoid CB1 Receptor Antagonists: Current Approaches for Therapeutics Development. Curr. Top. Med. Chem. 2019;19:1418–1435. doi: 10.2174/1568026619666190708164841.
73.Murineddu G., Asproni B., Corona P., Piras S., Lazzari P., Ruiu S., Legnani L., Toma L., Pinna G.A. Development of Oxygen-Bridged Pyrazole-Based Structures as Cannabinoid Receptor 1 Ligands. Molecules. 2019;24:1656. doi: 10.3390/molecules24091656.
74.Lohray B.B., Lohray V.B., Srivastava B. Novel Heterocyclic Compounds. WO2006/025069A2. 2006 Mar 9;
75.Banerjee K., Jain M., Vallabh A., Srivastava B., Joharapurkar A., Patel H. Synthesis and Biological Studies of a Novel CB1 Antagonist. Drug Res. 2015;66:33–40. doi: 10.1055/s-0035-1548848.
76.Mastinu A., Pira M., Pinna G.A., Pisu C., Casu M.A., Reali R., Marcello S., Murineddu G., Lazzari P. NESS06M reduces body weight with an improved profile relative to SR141716A. Pharmacol. Res. 2013;74:94–108. doi: 10.1016/j.phrs.2013.06.001.
77.Lazzari P., Serra V., Marcello S., Pira M., Mastinu A. Matabolic side effects induced by olanzapine treatment are neutralized by CB1 receptor antagonist compounds co-administration in female rats. Europ. Neuropsychopharmacol. 2017;27:667–678. doi: 10.1016/j.euroneuro.2017.03.010.
78.Fois G., Fattore L., Murineddu G., Salis A., Pintore G., Asproni B., Pinna G., Diana M. The novel cannabinoid antagonist SM-11 reduces hedonic aspect of food intake through a dopamine-dependent mechanism. Pharmacol. Res. 2016;113:108–115. doi: 10.1016/j.phrs.2016.08.012.
79.Dore A., Asproni B., Scampuddu A., Gessi S., Murineddu G., Cichero E., Fossa P., Merighi S., Bencivenni S., Pinna G.A. Synthesis, molecular modelling and SAR study of novel pyrazolo(5,1-f)(1,6)naphthyridines as CB2 receptor antagonists/inverse agonists. Bioorg. Med. Chem. 2016;24:5291–5301. doi: 10.1016/j.bmc.2016.08.055.

Studies

Conditions

Cannabinoids and active compounds

Related research

Abstract

Untitled section

Article notes

Untitled section

Author notes

1. Introduction

2. (5,5)-Condensed Pyrazole Derivatives

2.1. 1,4-dihydroindeno(1,2-c)pyrazole-Based Derivatives

2.2. Benzofuro(3,2-c)pyrazol-Based Derivatives (V)

2.3. 1,4-Dihydrothieno(2′,3′-4,5)cyclopenta(1,2-c)pyrazole-Based Derivatives (VII) and 1,4-Dihydrothieno(3′,2′-4,5)cyclopenta(1,2-c])pyrazole-Based Derivatives (X)

2.4. 1,4-Dihydropyrazolo(3,4-a)pyrrolizine-Based Derivatives (XV)

3. (5,6)-Condensed Pyrazole Derivatives

3.1. 4,5-Dihydro-1H-benzo(g)indazole-Based Derivatives (II)

3.2. 4,5-Dihydro-1H-thieno(2,3-g)indazole-Based Derivatives (VIII) and 4,5-Dihydro-1H-thieno(3,2-g)indazole-Based Derivatives (XI)

3.3. 1,5-Dihydroisothiochromen([4,3-c)pyrazole-Based Derivatives (XIII) and 1,4-Dihydrothiochromeno(4,3-c)pyrazole-Based Derivatives (XIV)

3.4. 4,5-Dihydro-1H-Pyrazolo(4,3-g)indolizine-Based Derivatives (XVI)

4. (5,7)-Condensed Pyrazole Derivatives

4.1. 1,4,5,6-Tetrahydrobenzo(6,7])cyclohepta(1,2-c]pyrazole-Based Derivatives (III)

4.2. 4,5-Dihydro-1H-benzo(2,3)oxepino(4,5-c)pyrazole-Based Derivatives (VI)

4.3. 1,4,5,6-Tetrahydrothieno(2′,3′-6,7])cyclohepta(1,2-c)pyrazole-Based Derivatives (IX) and 1,4,5,6-Tetrahydrothieno(3′,2′-6,7)cyclohepta(1,2-c)pyrazole-Based Derivatives (XII)

4.4. 1,4,5,6-Tetrahydropyrazolo(3,4-c)pyrrolo(1,2-a)azepine-Based Derivatives (XVII)

5. (5,8)-Condensed Pyrazole Derivatives

4,5,6,7-Tetrahydro-1H-benzo(7,8)cyclooct(1,2-c)pyrazole-Based Derivatives (IV)

6. Miscellaneous Derivatives

7. Conclusions

Author Contributions

Funding

Conflicts of Interest

Footnotes

Footnote Group

References

Untitled section

References

Additional materials