Emerging strategies targeting CB2 cannabinoid receptor: Biased agonism and allosterism

During these last years, the CB₂ cannabinoid receptor has emerged as a potential anti-inflammatory target in diseases such as multiple sclerosis, amyotrophic lateral sclerosis, Huntington's disease, ischemic stroke, autoimmune diseases, osteoporosis, and cancer. However, the development of clinically useful CB₂ agonists reveals to be very challenging. Allosterism and biased-signaling mechanisms at CB₂ receptor may offer new avenues for the development of improved CB₂ receptor-targeted therapies. Although there has been some exploration of CB₁ receptor activation by new CB₁ allosteric or biased-signaling ligands, the CB₂ receptor is still at initial stages in this domain. In an effort to understand the molecular basis behind these pharmacological approaches, we have analyzed and summarized the structural data reported so far at CB₂ receptor.

Study of Meldrum's Acid Cyclization Reactions

On the basis of the cyclization reactions reported by Danishefsky et al. of Meldrum's acid hydroxylethyl and anilinoethyl derivatives, the cyclization of the sulfamidomethylene and ureidomethylene derivatives was attempted without success. To understand the lack of reactivity of these compounds versus the successful cyclization of the ethyl derivatives, the corresponding mechanisms of reaction for both processes have been explored by means of MP2/6-311+G(d,p) calculations in an aqueous environment. The conformational analysis of all of these structures revealed that, while for the ethyl derivatives the minimum energy conformation corresponds to that of the cyclization initiating structure, for the methylene analogues the entrance channel conformations are substantially less stable than the energy minimum. Intramolecular hydrogen bonds were found in all of the energy minima as well as in the cyclization initiating conformations as determined by analysis of their electron density. The potential energy surfaces for the successful and unsuccessful cyclization processes were obtained at room temperature and 100 °C. Comparison of both processes allows rationalization that the lack of reactivity of the methylene derivatives can be thermodynamically explained based not only on the strength of the intramolecular hydrogen bond formed in their energy minima but also by the energy penalty needed to reach the entrance channel conformation and by the calculated energy barriers.

Chromenopyrazole, a Versatile Cannabinoid Scaffold with in Vivo Activity in a Model of Multiple Sclerosis

A combination of molecular modeling and structure-activity relationship studies has been used to fine-tune CB2 selectivity in the chromenopyrazole ring, a versatile CB1/CB2 cannabinoid scaffold. Thus, a series of 36 new derivatives covering a wide range of structural diversity has been synthesized, and docking studies have been performed for some of them. Biological evaluation of the new compounds includes, among others, cannabinoid binding assays, functional studies, and surface plasmon resonance measurements. The most promising compound [43 (PM226)], a selective and potent CB2 agonist isoxazole derivative, was tested in the acute phase of Theiler's murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD), a well-established animal model of primary progressive multiple sclerosis. Compound 43 dampened neuroinflammation by reducing microglial activation in the TMEV.

Cannabinoid receptor 2 (CB2) agonists and antagonists: a patent update

INTRODUCTION

Modulation of the CB2 receptor is an interesting approach for pain and inflammation, arthritis, addictions, neuroprotection, and cancer, among other possible therapeutic applications, and is devoid of central side effects.

AREAS COVERED

This review highlights the novel scaffolds for CB2 ligands and the diverse therapeutic applications for CB2 modulators disclosed in patents published since 2012.

EXPERT OPINION

Structural diversity of CB2 modulator scaffolds characterized the patent literature. Several CB2 agonists reached clinical Phase II for pain management and inflammation. Other therapeutic applications need to be explored such as neuroprotection and/or neurodegeneration.

Allosteric Modulators of the CB1 Cannabinoid Receptor: A Structural Update Review

In 2005, the first evidence of an allosteric binding site at the CB₁R was provided by the identification of three indoles of the company Organon that were allosteric enhancers of agonist binding affinity and, functionally, allosteric inhibitors of agonist activity. Since then, structure–activity relationships of indoles as CB₁R modulators have been reported. Targeting the allosteric site on CB₁R, new families structurally based on urea and on 3-phenyltropane analogs of cocaine have been discovered as CB₁R-negative allosteric modulators (NAMs), respectively, by Prosidion and by the Research Triangle Park. Endogenous allosteric ligands of different nature have been identified more recently. Thus, the therapeutic neuroprotection application of lipoxin A4, an arachidonic acid derivative, as an allosteric enhancer of CB₁R activity has been confirmed in vivo. It was also the case of the steroid hormone, pregnenolone, whose negative allosteric effects on Δ⁹-tetrahydrocannabinol (Δ⁹-THC) were reproduced in vivo in a behavioral tetrad model and in food intake and memory impairment assays. Curiously, the peroxisome proliferator-activated receptor-γ agonist fenofibrate or polypeptides such as pepcan-12 have been shown to act on the endocannabinoid system through CB₁R allosteric modulation. The mechanistic bases of the effects of the phytocannabinoid cannabidiol (CBD) are still not fully explained. However, there is evidence that CBD behaves as an NAM of Δ⁹-THC- and 2-AG. Allosteric modulation at CB₁R offers new opportunities for therapeutic applications. Therefore, further understanding of the chemical features required for allosteric modulation as well as their orthosteric probe dependence may broaden novel approaches for fine-tuning the signaling pathways of the CB₁R.

Synthesis, pharmacological evaluation and docking studies of pyrrole structure-based CB2 receptor antagonists

During the last years, there has been a continuous interest in the development of cannabinoid receptor ligands that may serve as therapeutic agents and/or as experimental tools. This prompted us to design and synthesize analogues of the CB2 receptor antagonist N-fenchyl-5-(4-chloro-3-methyl-phenyl)-1-(4-methyl-benzyl)-1H-pyrazole-3-carboxamide (SR144528). The structural modifications involved the bioisosteric replacement of the pyrazole ring by a pyrrole ring and variations on the amine carbamoyl substituents. Two of these compounds, the fenchyl pyrrole analogue 6 and the myrtanyl derivative 10, showed high affinity (Ki in the low nM range) and selectivity for the CB2 receptor and both resulted to be antagonists/inverse agonists in [(35)S]-GTPγS binding analysis and in an in vitro CB2 receptor bioassay. Cannabinoid receptor binding data of the series allowed identifying steric constraints within the CB2 binding pocket using a study of Van der Waals' volume maps. Glide docking studies revealed that all docked compounds bind in the same region of the CB2 receptor inactive state model.

Selective, nontoxic CB(2) cannabinoid o-quinone with in vivo activity against triple-negative breast cancer

Triple-negative breast cancer (TNBC) represents a subtype of breast cancer characterized by high aggressiveness. There is no current targeted therapy for these patients whose prognosis, as a group, is very poor. Here, we report the synthesis and evaluation of a potent antitumor agent in vivo for this type of breast cancer designed as a combination of quinone/cannabinoid pharmacophores. This new compound (10) has been selected from a series of chromenopyrazolediones with full selectivity for the nonpsychotropic CB2 cannabinoid receptor and with efficacy in inducing death of human TNBC cell lines. The dual concept quinone/cannabinoid was supported by the fact that compound 10 exerts antitumor effect by inducing cell apoptosis through activation of CB2 receptors and through oxidative stress. Notably, it did not show either cytotoxicity on noncancerous human mammary epithelial cells nor toxic effects in vivo, suggesting that it may be a new therapeutic tool for the management of TNBC.

Adamantyl analogues of paracetamol as potent analgesic drugs via inhibition of TRPA1

Paracetamol also known as acetaminophen, is a widely used analgesic and antipyretic agent. We report the synthesis and biological evaluation of adamantyl analogues of paracetamol with important analgesic properties. The mechanism of nociception of compound 6a/b, an analog of paracetamol, is not exerted through direct interaction with cannabinoid receptors, nor by inhibiting COX. It behaves as an interesting selective TRPA1 channel antagonist, which may be responsible for its analgesic properties, whereas it has no effect on the TRPM8 nor TRPV1 channels. The possibility of replacing a phenyl ring by an adamantyl ring opens new avenues in other fields of medicinal chemistry.

Combining rimonabant and fentanyl in a single entity: preparation and pharmacological results

Based on numerous pharmacological studies that have revealed an interaction between cannabinoid and opioid systems at the molecular, neurochemical, and behavioral levels, a new series of hybrid molecules has been prepared by coupling the molecular features of two wellknown drugs, ie, rimonabant and fentanyl. The new compounds have been tested for their affinity and functionality regarding CB₁ and CB₂ cannabinoid and μ opioid receptors. In [³⁵S]-GTPγS (guanosine 5′-O-[gamma-thio]triphosphate) binding assays from the post-mortem human frontal cortex, they proved to be CB₁ cannabinoid antagonists and μ opioid antagonists. Interestingly, in vivo, the new compounds exhibited a significant dual antagonist action on the endocannabinoid and opioid systems.

Synthetic cannabinoid quinones: preparation, in vitro antiproliferative effects and in vivo prostate antitumor activity

Chromenopyrazolediones have been designed and synthesized as anticancer agents using the multi-biological target concept that involves quinone cytotoxicity and cannabinoid antitumor properties. In cell cytotoxicity assays, these chromenopyrazolediones have antiproliferative activity against human prostate cancer and hepatocellular carcinoma. It has been shown that the most potent, derivative 4 (PM49), inhibits prostate LNCaP cell viability (IC₅₀ = 15 μM) through a mechanism involving oxidative stress, PPARγ receptor and partially CB₁ receptor. It acts on prostate cell growth by causing G₀/G₁ phase arrest and triggering apoptosis as assessed by flow cytometry measurements. In the in vivo treatment, compound 4 at 2 mg/kg, blocks the growth of LNCaP tumors and reduces the growth of PC-3 tumors generated in mice. These studies suggest that 4 is a good potential anticancer agent against hormone-sensitive prostate cancer.

Ghrelin-induced orexigenic effect in rats depends on the metabolic status and is counteracted by peripheral CB1 receptor antagonism

Ghrelin is an endogenous regulator of energy homeostasis synthesized by the stomach to stimulate appetite and positive energy balance. Similarly, the endocannabinoid system is part of our internal machinery controlling food intake and energy expenditure. Both peripheral and central mechanisms regulate CB1-mediated control of food intake and a functional relationship between hypothalamic ghrelin and cannabinoid CB1 receptor has been proposed. First of all, we investigated brain ghrelin actions on food intake in rats with different metabolic status (negative or equilibrate energy balance). Secondly, we tested a sub-anxiogenic ultra-low dose of the CB1 antagonist SR141716A (Rimonabant) and the peripheral-acting CB1 antagonist LH-21 on ghrelin orexigenic actions. We found that: 1) central administration of ghrelin promotes food intake in free feeding animals but not in 24 h food-deprived or chronically food-restricted animals; 2) an ultra-low dose of SR141716A (a subthreshold dose 75 folds lower than the EC₅₀ for induction of anxiety) completely counteracts the orexigenic actions of central ghrelin in free feeding animals; 3) the peripheral-restricted CB1 antagonist LH-21 blocks ghrelin-induced hyperphagia in free feeding animals. Our study highlights the importance of the animaĺs metabolic status for the effectiveness of ghrelin in promoting feeding, and suggests that the peripheral endocannabinoid system may interact with ghrelińs signal in the control of food intake under equilibrate energy balance conditions.

Description of a bivalent cannabinoid ligand with hypophagic properties

A series of bivalent cannabinoid ligands is proposed. The synthesis of double amides based on the rimonabant structure separated by an alkyl chain and the evaluation of their affinities for cannabinoid receptors are reported. The data of 4d confirmed that a bivalent structure is a suitable scaffold for CB1 cannabinoid receptor binding. The compound 4d was selected for in vitro and in vivo pharmacological evaluations. Moreover, intraperitoneal administration of 4d to food-deprived rats resulted in a dose-dependent inhibition of feeding that was maintained up to 240 min.

Anti-obesity efficacy of LH-21, a cannabinoid CB(1) receptor antagonist with poor brain penetration, in diet-induced obese rats

BACKGROUND AND PURPOSE

Peripheral blockade of cannabinoid CB(1) receptors has been proposed as a safe and effective therapy against obesity, putatively devoid of the adverse psychiatric side effects of centrally acting CB(1) receptor antagonists. In this study we analysed the effects of LH-21, a peripherally acting neutral cannabinoid receptor antagonist with poor brain penetration, in an animal model of diet-induced obesity.

EXPERIMENTAL APPROACH

To induce obesity, male Wistar rats were fed a high-fat diet (HFD; 60 kcal% fat) whereas controls received a standard diet (SD; 10 kcal% fat). Following 10 weeks of feeding, animals received a daily i.p. injection of vehicle or 3 mg·kg(-1) LH-21 for 10 days. Plasma and liver samples were used for biochemical analyses whereas visceral fat-pad samples were analysed for lipid metabolism gene expression using real-time RT-PCR. In addition, the potential of LH-21 to interact with hepatic cytochrome P450 isoforms and cardiac human Ether-à-go-go Related Gene (hERG) channels was evaluated.

KEY RESULTS

LH-21 reduced feeding and body weight gain in HFD-fed animals compared with the control group fed SD. In adipose tissue, this effect was associated with decreased gene expression of: (i) leptin; (ii) lipogenic enzymes, including SCD-1; (iii) CB(1) receptors; and (iv) both PPARα and PPARγ. Although there were no significant differences in plasma parameters between HFD- and SD-fed rats, LH-21 did not seem to induce hepatic, cardiac or renal toxicity.

CONCLUSIONS AND IMPLICATIONS

These results support the hypothesis that treatment with the peripherally neutral acting CB(1) receptor antagonist, LH-21, may promote weight loss through modulation of visceral adipose tissue.

Chromenopyrazoles: non-psychoactive and selective CB₁ cannabinoid agonists with peripheral antinociceptive properties

The unwanted psychoactive effects of cannabinoid receptor agonists have limited their development as medicines. These CB₁-mediated side effects are due to the fact that CB₁ receptors are largely expressed in the central nervous system (CNS). As it is known that CB₁ receptors are also located peripherally, there is growing interest in targeting cannabinoid receptors located outside the brain. A library of chromenopyrazoles designed analogously to the classical cannabinoid cannabinol were synthesized, characterized, and tested for cannabinoid activity. Radioligand binding assays were used to determine their affinities at CB₁ and CB₂ receptors. Structural features required for CB₁/CB₂ affinity and selectivity were explored by molecular modeling. Some compounds in the chromenopyrazole series were observed to be selective CB₁ ligands. These modeling studies suggest that full CB₁ selectivity over CB₂ can be explained by the presence of a pyrazole ring in the structure. The functional activities of selected chromenopyrazoles were evaluated in isolated tissues. In vivo behavioral tests were then carried out on the most effective CB₁ cannabinoid agonist, 13 a. Chromenopyrazole 13 a did not induce modifications in any of the tested parameters on the mouse cannabinoid tetrad, thus discounting CNS-mediated effects. This lack of agonistic activity in the CNS suggests that this compound does not readily cross the blood-brain barrier. Moreover, 13 a can induce antinociception in a rat peripheral model of orofacial pain. Taking into account the negative results obtained with the hot-plate test, the antinociception induced by 13 a in the orofacial test could be mediated through peripheral mechanisms.

Discovery of Potent Dual PPARα Agonists/CB1 Ligands

This letter describes the synthesis and in vitro and in vivo evaluation of dual ligands targeting the cannabinoid and peroxisome proliferator-activated receptors (PPAR). These compounds were obtained from fusing the pharmacophores of fibrates and the diarylpyrazole rimonabant, a cannabinoid receptor antagonist. They are the first examples of dual compounds with nanomolar affinity for both PPARα and cannabinoid receptors. Besides, lead compound 2 proved to be CB1 selective. Unexpectedly, the phenol intermediates tested were equipotent (compound 1 as compared to 2) or even more potent (compound 3 as compared with 4). This discovery opens the way to design new dual ligands.

The structure of Rimonabant in the solid state and in solution: an experimental and theoretical study

The X-ray molecular structure of Rimonabant methanol solvate has been determined together with the (1)H, (13)C and (15)N NMR spectra in acetone solution. B3YP/6-311++G(d,p) calculations have been performed out to determine two minimum energy conformations, on these geometries GIAO calculations were carried out to obtain the corresponding absolute shieldings that were compared with the experimental chemical shifts.

Central versus peripheral antagonism of cannabinoid CB1 receptor in obesity: effects of LH-21, a peripherally acting neutral cannabinoid receptor antagonist, in Zucker rats

The endogenous cannabinoid system plays an important modulatory role in feeding behaviour and metabolism, acting at both central and peripheral levels. Chronic administration of cannabinoid CB(1) receptor antagonists has been found to be effective in experimental obesity. However, clinically available cannabinoid receptor antagonists are inverse agonists that can target CB(1) receptors located in both central circuits regulating appetite and motivation and in peripheral organs regulating metabolism and energy expenditure. This profile complicates understanding of cannabinoid CB(1) receptor blockade as a therapeutic strategy in obesity and metabolic disorders. This review aims to explore the relevance of both inverse agonism and peripheral cannabinoid receptor blockade on the beneficial actions of chronic cannabinoid receptor blockade, by comparing the actions of the reference antagonist/inverse agonist rimonabant and the newly designed drug LH-21. LH-21 is a triazol derivative and a neutral cannabinoid receptor antagonist; it has a poor penetration rate into the central nervous system. When given acutely it decreases food intake and enhances the anorectic actions of oleoylethanolamide, a feeding suppressant lipid that acts on peripheral sensory terminals in a similar way as rimonabant. Unlike rimonabant, chronic administration of LH-21 (3 mg/kg) reduces feeding but does not improve hypertriglyceridaemia or hypercholesterolaemia; nor does it reduce liver fat deposits in Zucker rats. These results suggest that the inverse agonism and/or the antagonism of central cannabinoid CB(1) receptors are necessary for the metabolic benefits of cannabinoid CB(1) receptor blockade, but not for the appetite reduction.

CB1 cannabinoid antagonists: structure-activity relationships and potential therapeutic applications

During the last decade there has been a growing interest towards the modulation of the cannabinoid CB1 receptor. The identification of CB1 cannabinoid receptor antagonists has been one of the major advances in cannabinoid research. Thus, the development of these ligands has opened new therapeutic applications. Since the discovery of the first cannabinoid receptor antagonist, rimonabant, by Sanofi in 1994, a large number of structural variations within this chemical series of 1,5-diarylpyrazoles have been described. So far, all attempts to identify novel structures for CB1 antagonists have been based on one or more pharmacophoric elements of the rimonabant structure. The advanced clinical trials of rimonabant confirm the therapeutic potential value of CB1 antagonists for the treatment of obesity. In addition, the results of pharmacological and clinical studies reveal other effective pharmacotherapeutic applications. The current review will mainly focus on the structure-activity relationships that have been established for antagonists/inverse agonists that bind to the CB1 cannabinoid receptors and on their therapeutic applications.

Discovery of 1,1-dioxo-1,2,6-thiadiazine-5-carboxamide derivatives as cannabinoid-like molecules with agonist and antagonist activity

A series of new 2-substituted 1,1-dioxo-1,2,6-thiadiazine-5-carboxylate derivatives have been prepared from monosubstituted sulfamides in order to obtain N-substituted 1,1-dioxo-1,2,6-thiadiazine-5-carboxamides as novel cannabinoid derivatives, analogues of Rimonabant (SR141716A). Their potential functional activity on cannabinoid receptors has been evaluated in vitro and in vivo in mice, showing that two compounds (37 and 39) behave as cannabinoid agonists in vitro. Their potency is lower than that of the reference compound, WIN 55,212-2, but their efficacy is similar to that of this cannabinoid agonist, although no in vivo activity is observed. Another derivative (38) behaves as a cannabinoid antagonist both in vitro and in vivo, being its efficacy and potency similar to that of the well-known antagonist SR141716A.

Novel sulfamide analogs of oleoylethanolamide showing in vivo satiety inducing actions and PPARalpha activation

Long chain saturated and unsaturated alkyl sulfamide and propyl sulfamide derivatives, analogs of oleoylethanolamide, have been synthesized and evaluated in vivo and in vitro as peroxisome proliferator activated receptor alpha (PPARalpha) activators. Additionally, the anorexic effects of the new compounds have been studied in vivo in food-deprived rats. Among the active compounds N-octadecyl-N'-propylsulfamide (7) has been identified as a potent hypolipidemic compound, a potent feeding suppressant, and a concentration-dependent activator of PPARalpha.

Antiobesity effects of the novel in vivo neutral cannabinoid receptor antagonist 5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-3-hexyl-1H-1,2,4-triazole – LH 21

The present study evaluates the pharmacological profile of the new neutral cannabinoid CB1 receptor antagonist 5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-3-hexyl-1H-1,2,4-triazole -LH-21- on feeding behavior and alcohol self-administration in rats, two behaviors inhibited by cannabinoid CB1 receptor antagonists. Administration of LH-21 (0.03, 0.3 and 3 mg/kg) to food-deprived rats resulted in a dose-dependent inhibition of feeding. Subchronic administration of LH-21 reduced food intake and body weight gain in obese Zucker rats. Acute effects on feeding were not associated with anxiety-like behaviors, or induction of complex motor behaviors such as grooming or scratching sequences, usually observed after central administration of cannabinoid receptor blockers with inverse agonist properties. LH-21 did not markedly reduce alcohol self-administration (30% reduction observed only at a high dose of 10 mg/kg). This pharmacological pattern partially overlaps that of the reference cannabinoid CB1 receptor antagonist N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methylpyrazole-3-carboxamide, SR141716A, (0.3, 1 and 3 mg/kg) that reduced feeding and alcohol self-administration with similar efficacy. In vitro analysis of blood-brain barrier permeability using a parallel artificial membrane permeation assay demonstrated that LH-21 has lower permeation through membranes than SR141716A. That was confirmed in vivo by studies showing lower potency of peripherally injected LH-21 when compared to SR141716A to antagonize motor depression induced by intracerebroventricular administration of the CB1 agonist CP55,940. The neutral antagonist profile and the lower penetration into the brain of LH-21 favour this class of antagonists with respect to reference inverse agonists for the treatment of obesity because they potentially will display reduced side effects.

Structural–activity relationship study on C-4 carbon atom of the CB1 antagonist SR141716: synthesis and pharmacological evaluation of 1,2,4-triazole-3-carboxamides

A series of 1,2,4-triazole-3-carboxamides has been prepared from alkyl-1,2,4-triazole-3-carboxylates under mild conditions. The ability of these triazoles to displace [3H]-CP55940 from CB1 cannabinoid receptor was measured. However, they showed only poor to moderate binding affinities, indicating that substitution of the C-4 pyrazole atom of the CB1 reference compound SR141716 by a nitrogen atom results in loss of affinity. Further investigations for functionality indicated that the compound 6a exhibited significant cannabinoid antagonistic properties in the mouse vas deferens functional assay. This leads us to the conclusion that 6a binds at a different CB1 binding site or at a new cannabinoid receptor subtype.

Homology models of the cannabinoid CB1 and CB2 receptors. A docking analysis study

The 3D models of both CB1 and CB2 human receptors have been established by homology modeling using as template the X-ray structure of bovine Rhodopsin (code pdb: 1F88) a G-protein-coupled receptor (GPCR). A recursive approach comprising sequence alignment and model building was used to build both models, followed by the refinement of non-conserved regions. The cannabinoid system has been studied by means of docking techniques, using the 3D models of both CB1 and CB2 and well known reference inverse agonist/antagonist compounds. An approach based on the flexibility of the structures has been used to model the receptor-ligand complexes. The structural effects of ligand binding were studied and analyzed on the basis of hydrogen bond interactions, and binding energy calculations. Potential interaction sites of the receptor were determined from analysis of the difference accessible surface area (DASA) study of the protein with and without ligand.

Discovery of 5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-3-hexyl-1H-1,2,4-triazole, a Novel in Vivo Cannabinoid Antagonist Containing a 1,2,4-Triazole Motif

A new series of 1,2,4-triazoles have been prepared and the evaluation of their cannabinoid properties have been carried out. Compound 8 showed cannabinoid silent antagonist activity in mouse vas deferens and guinea pig ileum preparations and in vivo assays (cannabinoid tetrad) in mouse. It did not have intrinsic activity in these bioassays, and therefore, it did not behave as a partial agonist or an inverse agonist.

Cannabinoids and Neuropathic Pain

After a brief overview of the endocannabinoid system (CB receptors, and endocannabinoids) and of the cannabinergic ligands, some general issues related to cannabinoids and pain are commented. Finally, the most important findings regarding cannabinoids and neuropathic pain are discussed in detail.

Fentanyl and its analogue N-(1-phenylpyrazol-3-yl)-N-[1-(2-phenylethyl)-4-piperidyl]propanamide: 1H- and 13C-NMR spectroscopy, X-ray crystallography, and theoretical calculations

The oxalate salts and free bases of fentanyl and N-[1-(2-phenylethyl)-4-piperidyl]-N-(1-phenyl-4-pyrazolyl)propanamide, a new lead compound for long-acting analgesia, have been characterized by (1)H- and (13)C-NMR spectroscopy. The crystal structure of the hydrochloride of N-[1-(2-phenylethyl)-4-piperidyl]-N-(1-phenyl-4-pyrazolyl)propanamide monohydrate has been determined. Two centrosymmetrically related cations, joined through C(phenyl)-H em leader pi contacts, encapsulate a large void that contains pairs of anions and bridged water molecules into a zero-dimensional (0D) supramolecular motif. The cations are linked to this framework via N(+)H em leader Cl(-) contacts. GIAO/B3LYP calculations have been carried out to compare the experimental (13)C chemical shifts with the absolute shieldings thus calculated. The protonation of both molecules takes place on the piperidine ring (axial protonation), as has been verified both in the solid state (X-ray) and in solution (NMR).

Synthesis and analgesic activity of a series of new azaalkane bis-guanidinium and bis(2-aminoimidazolinium) compounds

In the present paper, we wish to report the synthesis and antinociceptive activity of a series of new azaalkane bis(2-aminoimidazolinium) compounds from which, N,N'-di(4,5-dihydro-1H-imidazol-2-yl)-3-aza-1,6-hexanediamine 2a has shown the best analgesic properties in vivo in two different assays (i.e., acetic acid-induced writhing test and hot-plate test in mice), as well as oral bioavailability.