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

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

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.

Direct Catalytic Symmetrical, Unsymmetrical N,N-Dialkylation and Cyclization of Acylhydrazides Using Alcohols

Herein, direct N,N-dialkylation of acylhydrazides using alcohols is reported. This catalytic protocol provides one-pot synthesis of both symmetrical and unsymmetrical N,N-disubstituted acylhydrazides using an assortment of primary and secondary alcohols with remarkable selectivity and excellent yields. Interestingly, the use of diols resulted in intermolecular cyclization of acylhydrazides, and such products are privileged structures in biologically active compounds. Water is the only byproduct, which makes this catalytic protocol sustainable and environmentally benign.

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

8-Chloro-1-(2',4'-dichlorophenyl)-N-piperidin-1-yl-1,4,5,6-tetrahydrobenzo[6,7]cyclohepta[1,2-c]pyrazole-3-carboxamide 9a was discovered as potent and selective CB1 antagonist by part of our group few years ago. In particular it was reported to have an affinity towards the CB1 cannabinoid receptor (CB1R), expressed as Ki, of 0.00035 nM. Nevertheless significantly divergent data were reported for the same compound from other laboratories. To unequivocally define the receptor profile of 9a, we have critically reviewed both its synthesis approach and binding data. Here we report that, in contrast to our previously reported data, 9a showed a Ki value for CB1R in the order of nanomolar rather than of fentomolar range. The new determined receptor profile of 9a was also ascertained for analogue derivatives 9b-i, as well as for 12. Moreover, the structural features of the synthesized compounds necessary for CB1R were investigated. Amongst the novel series, effects on CB1R intrinsic activity was highlighted due to the substituents at the position 3 of the pyrazole ring of the 1,4,5,6-tetrahydrobenzo[6,7]cyclohepta[1,2-c]pyrazole scaffold. Although the cannabinoid receptor profile of 9a was reviewed in this work, the relevance of this compound in CB1R antagonist based drug discovery is confirmed.

NESS06SM reduces body weight with an improved profile relative to SR141716A

We have recently synthesized a new series of 4,5-dihydrobenzo-oxa-cycloheptapyrazole derivatives with the aim to discover novel CB1 antagonist agents characterized by anti-obesity activity comparable to that of SR141716A but with reduced adverse effects such as anxiety and depression. Within the novel class, the CB1 antagonist 8-chloro-1-(2,4-dichlorophenyl)-N-piperidin-1-yl-4,5-dihydrobenzo-1H-6-oxa-cyclohepta(1,2-c)pyrazole-3-carboxamide (NESS06SM) has been selected as lead compound. We found that NESS06SM is a CB1 neutral antagonist, characterized by poor blood-brain barrier permeability. Moreover, NESS06SM chronic treatment determined both anti-obesity effect and cardiovascular risk factor improvement in C57BL/6N Diet Induced Obesity (DIO) mice fed with fat diet (FD mice). In fact, the mRNA gene expression in Central Nervous System (CNS) and peripheral tissues by real time PCR, showed a significant increase of orexigenic peptides and a decrease of anorexigenic peptides elicited by NESS06SM treatment, compared to control mice fed with the same diet. Moreover, in contrast to SR141716A treatment, the chronic administration of NESS06SM did not change mRNA expression of both monoaminergic transporters and neurotrophins highly related with anxiety and mood disorders. Our results suggest that NESS06SM reduces body weight and it can restore the disrupted expression profile of genes linked to the hunger-satiety circuit without altering monoaminergic transmission probably avoiding SR141716A side effects. Therefore the novel CB1 neutral antagonist could represent a useful candidate agent for the treatment of obesity and its metabolic complications.

In silico investigation of interactions between human cannabinoid receptor-1 and its antagonists

Cannabinoid receptor-1 (CB(1)) is widely expressed in the central nervous system and plays a vital role in regulating food intake and energy expenditure. CB(1) antagonists such as Rimonabant have been used in clinic to inhibit food intake, and therefore reduce body weight in obese animals and humans. To investigate the binding modes of CB(1) antagonists to the receptor, both receptor- and ligand-based methods were implemented in this study. At first, a pharmacophore model was generated based on 31 diverse CB(1) antagonists collected from literature. A test set validation and a simulated virtual screening evaluation were then performed to verify the reliability and discriminating ability of the pharmacophore. Meanwhile, the homology model of CB(1) receptor was constructed based on the crystal structure of human β (2) adrenergic receptor (β (2)-AR). Several classical antagonists were then docked into the optimized homology model with induced fit docking method. A hydrogen bond between the antagonists and Lys192 on the third transmembrane helix of the receptor was formed in the docking study, which has proven to be critical for receptor-ligand interaction by biological experiments. The structure obtained from induced fit docking was then confirmed to be a reliable model for molecular docking from the result of the simulated virtual screening. The consistency between the pharmacophore and the homology structure further proved the previous observation. The built receptor structure and antagonists' pharmacophore should be useful for the understanding of inhibitory mechanism and development of novel CB(1) antagonists.

Endocannabinoid tone versus constitutive activity of cannabinoid receptors

This review evaluates the cellular mechanisms of constitutive activity of the cannabinoid (CB) receptors, its reversal by inverse agonists, and discusses the pitfalls and problems in the interpretation of the research data. The notion is presented that endogenously produced anandamide (AEA) and 2-arachidonoylglycerol (2-AG) serve as autocrine or paracrine stimulators of the CB receptors, giving the appearance of constitutive activity. It is proposed that one cannot interpret inverse agonist studies without inference to the receptors' environment vis-à-vis the endocannabinoid agonists which themselves are highly lipophilic compounds with a preference for membranes. The endocannabinoid tone is governed by a combination of synthetic pathways and inactivation involving transport and degradation. The synthesis and degradation of 2-AG is well characterized, and 2-AG has been strongly implicated in retrograde signalling in neurons. Data implicating endocannabinoids in paracrine regulation have been described. Endocannabinoid ligands can traverse the cell's interior and potentially be stored on fatty acid-binding proteins (FABPs). Molecular modelling predicts that the endocannabinoids derived from membrane phospholipids can laterally diffuse to enter the CB receptor from the lipid bilayer. Considering that endocannabinoid signalling to CB receptors is a much more likely scenario than is receptor activation in the absence of agonist ligands, researchers are advised to refrain from assuming constitutive activity except for experimental models known to be devoid of endocannabinoid ligands.

Towards rational design of cannabinoid receptor 1 (CB1) antagonists for peripheral selectivity

CB1 receptor antagonists that are peripherally restricted were targeted. Compounds with permanent charge as well as compounds that have increased polar surface area were made and tested against CB1 for binding and activity. Sulfonamide and sulfamide with high polar surface area and good activity at CB1 were rationally designed and pharmacologically tested. Further optimization of these compounds and testing could lead to the development of a new class of therapeutics to treat disorders where the CB1 receptor system has been implicated.

A synthetic cannabinoid, CP55940, inhibits lipopolysaccharide-induced cytokine mRNA expression in a cannabinoid receptor-independent mechanism in rat cerebellar granule cells

OBJECTIVES

The inflammatory response plays an important role in the pathogenesis of many diseases in the central nervous system. Cannabinoids exhibit diverse pharmacological actions including anti-inflammatory activity. In this study, we tried to elucidate possible effects of cannabinoids on lipopolysaccharide (LPS)-induced expression of inflammatory cytokine mRNAs in rat cerebellar granule cells.

METHODS

Inhibitory effects of cannabinoids on cytokine induction in cerebellar granule cells were determined by RT-PCR method.

KEY FINDINGS

In these cells, both mRNA and protein of cannabinoid receptor 1 (CB(1) ), but not CB(2) , were expressed. LPS (1 µg/ml) produced a marked increase in the induction of inflammatory cytokines, including interleukin-1β, interleukin-6 and tumour necrosis factor-α. CP55940, a synthetic cannabinoid analogue, concentration-dependently inhibited inflammatory cytokine expression induced by LPS. On the other hand, the endocannabinoids 2-arachidonoylglycerol and anandamide were not able to inhibit this inflammatory response. Notably, a CB(1) /CB(2) antagonist NESS0327 (3 µm) did not reverse the inhibition of cytokine mRNA expression induced by CP55940. GPR55, a putative novel cannabinoid receptor, mRNA was also expressed in cerebellar granule cells. Although it has been suggested that G(q) associates with GPR55, cannabinoids including CP55940 did not promote phosphoinositide hydrolysis and consequent elevation of intracellular Ca([2+]) concentration. Furthermore, a putative GPR55 antagonist, cannabidiol, also showed a similar inhibitory effect to that of CP55940.

CONCLUSIONS

These results suggest that the synthetic cannabinoid CP55940 negatively modulates cytokine mRNA expression in cerebellar granule cells by a CB and GPR55 receptor-independent mechanism.

Efficient and highly regioselective synthesis of ethyl 1-(2,4-dichlorophenyl)-1H-pyrazole-3-carboxylates under ultrasound irradiation

A series of 14 ethyl 1-(2,4-dichlorophenyl)-1H-pyrazole-3-carboxylates has been synthesized from the cyclocondensation reaction of ethyl 4-methoxy-2-oxoalk[cycloalk]-3-enoates [EtO(2)CC(O)C(R(2))=C(R(1))OR, where R=H, Me; R(1)=Pr, Ph, 4-MeOC(6)H(4), 4-MeC(6)H(4), 4-FC(6)H(4), 4-ClC(6)H(4), 4-BrC(6)H(4), 4-NO(2)C(6)H(4), fur-2-yl; R(2)=H; R(1), R(2)=-(CH(2))(3)-, -(CH(2))(4)-, -(CH(2))(5)-, -(CH(2))(6)-, 3,4-dihydronaphth-2-yl] with 2,4-dichlorophenyl hydrazine hydrochloride under ultrasound irradiation with high regioselectivity and in 71-92% yields. The main goal of this methodology was the significant reduction of reaction times. The compounds were obtained after irradiation for 10-12 min. In addition, the structure of the ethyl 1H-pyrazole-3-carboxylates was supported by crystallographic data.

Synthesis and biological evaluation of bivalent ligands for the cannabinoid 1 receptor

Dimerization or oligomerization of many G-protein-coupled receptors (GPCRs), including the cannabinoid 1 (CB1) receptor, is now widely accepted and may have significant implications for medications development targeting these receptor complexes. A library of bivalent ligands composed of two identical CB1 antagonist pharmacophores derived from SR141716 linked by spacers of various lengths were developed. The affinities of these bivalent ligands at CB1 and CB2 receptors were determined using radiolabeled binding assays. Their functional activities were measured using GTP-γ-S accumulation and intracellular calcium mobilization assays. The results suggest that the nature of the linker and its length are crucial factors for optimum interactions of these ligands at CB1 receptor binding sites. Finally, selected bivalent ligands (5d and 7b) were able to attenuate the antinociceptive effects of the cannabinoid agonist CP55,940 (21) in a rodent tail-flick assay. These novel compounds may serve as probes that will enable further characterization of CB1 receptor dimerization and oligomerization and its functional significance and may prove useful in the development of new therapeutic approaches to G-protein-coupled receptor mediated disorders.

Zirconocene-mediated macrocyclizations of diynes containing di-o-methylphenylene spacers

The diynes 3,3',5,5'-tetramethyl-4,4'-di(pent-1-ynyl)biphenyl (4) and 3,3'',5,5''-tetramethyl-4,4''-di(hex-1-ynyl)terphenyl (9) undergo coupling with Cp(2)Zr(eta(2)-Me(3)SiC[triple bond]CSiMe(3))(py) to give dimeric macrocycles in moderate yields (16% for 4 and 26% for 9).