Imidazopyridine CB2 agonists: Optimization of CB2/CB1 selectivity and implications for in vivo analgesic efficacy

Cu(I)-Catalyzed Three-Component Annulation for the Synthesis of 3-Acyl Imidazo[1, 5-a]Pyridines from 2-Pyridinyl-Substituted p-Quinone Methides, Terminal Alkynes, and TsN3 Using O2 as the Oxygen Source

Currently, most conventional methods to achieve imidazo[1,5-a]pyridines have limitations for the synthesis of 3-acyl imidazo[1,5-a]pyridines. Herein, a novel and efficient Cu(I)-catalyzed three-component annulation method for the synthesis of valuable 3-acyl imidazo[1,5-a]pyridines by the reaction of 2-pyridinyl-substituted p-QMs, terminal alkynes, and TsN3 in the presence of O2 under mild conditions have successfully been developed. The investigation indicated that molecular oxygen (O2) and TsN3, respectively, serving as oxygen and nitrogen sources, were essential for the successful completion of the reaction system.

C-C Bond Cleavage Mediated Reaction for Constructing 3-Carbonyl Imidazo[1,5-a] Pyridines from 1,3-Dicarbonyl Compounds and Pyridin-2-ylmethanamines

A [4 + 1] cyclization and C-C bond cleavage process mediated reaction for constructing 3-carbonyl imidazo[1,5-a] pyridines from 1,3-dicarbonyl compounds and pyridin-2-ylmethanamines has been developed. Various 1,3-dicarbonyl compounds are applicable, and selectivity could be achieved. Importantly, this strategy could be extended to an atom economy method by employing a cyclic 1,3-dicarbonyl compound, and it provided a new view for C-C bond cleavage reactions.

New thiazole-based derivatives as EGFR/HER2 and DHFR inhibitors: Synthesis, molecular modeling simulations and anticancer activity

New series of thiazole and imidazo[2,1-b]thiazole derivatives were synthesized and tested for their in vitro anticancer activity. Compounds 27, 34, 39 and 42-44 showed the best anticancer activity against the tested cancer cell lines with high safety profile and selectivity indices, especially MCF-7 breast cancer, compared to sorafenib. As an attempt to reveal their mode of cytotoxicity, EGFR, HER2 kinase and DHFR inhibition assays were performed. Compounds 39 and 43 were the most potent dual EGFR/HER2 kinase inhibitors, with IC₅₀ values of 0.153 (EGFR), 0.108 (HER2) and 0.122 (EGFR), 0.078 (HER2) μM, respectively. 39 and 42 were the best DHFR inhibitors showing IC₅₀ 0.291 and 0.123 μM, respectively. 39 and 43 induced their cytotoxicity via cell cycle arrest at G1/S and G1 phases, respectively, and apoptosis rather than necrosis in the MCF-7 breast cancer cell line. In vivo anti-breast cancer assay of 39 and 43 showed significant tumor volume reduction with recovered caspase-3 immunoexpression. Modeling study results proved the importance of the 5-(4-substituted phenyl)-imidazo[2,1-b]thiazole moiety and the hydrazide side chain for the anticancer activity. The most potent compounds showed good drug-likeness features and could be used as prototypes for further optimization. 39 could be an example of a multi-targeting anticancer agent that acts by inhibiting EGFR/HER2 kinase, DHFR enzymes and cellular apoptosis.

New β-carboline derivatives containing imidazolium as potential VEGFR2 inhibitors: synthesis, X-ray structure, antiproliferative evaluations, and molecular modeling

A series of new β-carboline derivatives containing an imidazolium moiety were designed and synthesized via the reaction of β-carboline-1-carboxaldehydes, acetyl chloride, primary amine, and formaldehyde. The antitumor activity of the synthesized compounds was examined against lung carcinoma (A549), gastric carcinoma (BGC-823), murine colon carcinoma (CT-26), liver carcinoma (Bel-7402) and breast carcinoma (MCF-7) cells. The results indicated that most compounds exhibited significant antiproliferative activity, in some cases greater than that of cisplatin, and compound 3z was found to be the most potent antiproliferative agent against A549, BGC823, CT-26, Bel-7402 and MCF-7 cell lines with an IC50 value of 2.7 ± 0.4, 2.7 ± 0.6, 2.4 ± 0.2, 3.2 ± 0.2, and 5.6 ± 0.3 μM, respectively. Combined with favorable in vitro potency, the antitumor efficacies of the selected compounds in mice were also evaluated. Compound 3z exhibited potent antitumor activity with a tumor inhibition rate of 48.6% in sarcoma 180 models. Preliminary investigations on the mechanisms of action revealed that compound 3z could dramatically inhibit EA.hy926 cell tube formation in a dose-dependent manner. Further investigation of the preliminary mechanism of action demonstrated that compound 3z had obvious angiogenesis inhibitory effects in the chicken chorioallantoic membrane (CAM) assay. The results of the docking study showed a good fitting of the new compounds 3o and 3z to the active site of VEGFR-2 with a docking score energy of -11.31 kcal per mole and -11.26 kcal per mole, respectively.

Recent synthetic methodologies for imidazo[1,5-a]pyridines and related heterocycles

Imidazo[1,5-a]pyridine is a significant structural component of a large number of agrochemicals and pharmaceuticals. The synthesis of imidazo[1,5-a]pyridine has been a subject of intense research for numerous decades. A large number of transformations are now available to conveniently access imidazo[1,5-a]pyridine from readily available starting materials. This review details the recent development in imidazo[1,5-a]pyridine construction involving cyclocondensation, cycloaddition, oxidative cyclization, and transannulation reactions.

Putative Synthetic Cannabinoids MEPIRAPIM, 5F-BEPIRAPIM (NNL-2), and Their Analogues Are T-Type Calcium Channel (CaV3) Inhibitors

Synthetic cannabinoid receptor agonists (SCRAs) are a large and growing class of new psychoactive substances (NPSs). Two recently identified compounds, MEPIRAPIM and 5F-BEPIRAPIM (NNL-2), have not been confirmed as agonists of either cannabinoid receptor subtype but share structural similarities with both SCRAs and a class of T-type calcium channel (Ca_V3) inhibitors under development as new treatments for epilepsy and pain. In this study, MEPIRAPIM and 5F-BEPIRAPIM and 10 systematic analogues were synthesized, analytically characterized, and pharmacologically evaluated using in vitro cannabinoid receptor and Ca_V3 assays. Several compounds showed micromolar affinities for CB₁ and/or CB₂, with several functioning as low potency agonists of CB₁ and CB₂ in a membrane potential assay. 5F-BEPIRAPIM and four other derivatives were identified as potential Ca_V3 inhibitors through a functional calcium flux assay (>70% inhibition), which was further confirmed using whole-cell patch-clamp electrophysiology. Additionally, MEPIRAPIM and 5F-BEPIRAPIM were evaluated in vivo using a cannabimimetic mouse model. Despite detections of MEPIRAPIM and 5F-BEPIRAPIM in the NPS market, only the highest MEPIRAPIM dose (30 mg/kg) elicited a mild hypothermic response in mice, with no hypothermia observed for 5F-BEPIRAPIM, suggesting minimal central CB₁ receptor activity.

Imidazo[1,5-a]pyridine derivatives: useful, luminescent and versatile scaffolds for different applications

In the last few years, imidazo[1,5-a]pyridine nuclei and derivatives have attracted growing attention due to their unique chemical structure and versatility, optical behaviours, and biological properties.

Synthesis of imidazo[1,5-a]pyridines via cyclocondensation of 2-(aminomethyl)pyridines with electrophilically activated nitroalkanes

Imidazo[1,5-a]pyridines were efficiently prepared via the cyclization of 2-picolylamines with nitroalkanes electrophilically activated in the presence of phosphorous acid in polyphosphoric acid (PPA) medium.

Cannabinoid Receptor Subtype 2 (CB2R) in a Multitarget Approach: Perspective of an Innovative Strategy in Cancer and Neurodegeneration

The cannabinoid receptor subtype 2 (CB2R) represents an interesting and new therapeutic target for its involvement in the first steps of neurodegeneration as well as in cancer onset and progression. Several studies, focused on different types of tumors, report a promising anticancer activity induced by CB2R agonists due to their ability to reduce inflammation and cell proliferation. Moreover, in neuroinflammation, the stimulation of CB2R, overexpressed in microglial cells, exerts beneficial effects in neurodegenerative disorders. With the aim to overcome current treatment limitations, new drugs can be developed by specifically modulating, together with CB2R, other targets involved in such multifactorial disorders. Building on successful case studies of already developed multitarget strategies involving CB2R, in this Perspective we aim at prompting the scientific community to consider new promising target associations involving HDACs (histone deacetylases) and σ receptors by employing modern approaches based on molecular hybridization, computational polypharmacology, and machine learning algorithms.

Innovative Therapeutic Potential of Cannabinoid Receptors as Targets in Alzheimer’s Disease and Less Well-Known Diseases

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The discovery of cannabinoid receptors at the beginning of the 1990s, CB1 cloned in 1990 and CB2 cloned in 1993, and the availability of selective and potent cannabimimetics could only be justified by the existence of endogenous ligands that are capable of binding to them. Thus, the characterisation and cloning of the first cannabinoid receptor (CB1) led to the isolation and characterisation of the first endocannabinoid, arachidonoylethanolamide (AEA), two years later and the subsequent identification of a family of lipid transmitters known as the fatty acid ester 2-arachidonoylglycerol (2-AG).

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The endogenous cannabinoid system is a complex signalling system that comprises transmembrane endocannabinoid receptors, their endogenous ligands (the endocannabinoids), the specific uptake mechanisms and the enzymatic systems related to their biosynthesis and degradation.

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The endocannabinoid system has been implicated in a wide diversity of biological processes, in both the central and peripheral nervous systems, including memory, learning, neuronal development, stress and emotions, food intake, energy regulation, peripheral metabolism, and the regulation of hormonal balance through the endocrine system.

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In this context, this article will review the current knowledge of the therapeutic potential of cannabinoid receptor as a target in Alzheimer’s disease and other less well-known diseases that include, among others, multiple sclerosis, bone metabolism, and Fragile X syndrome.

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The therapeutic applications will be addressed through the study of cannabinoid agonists acting as single drugs and multi-target drugs highlighting the CB2 receptor agonist.

Benzo[d]thiazol-2(3H)-ones as new potent selective CB2 agonists with anti-inflammatory properties

The high distribution of CB₂ receptors in immune cells suggests their important role in the control of inflammation. Growing evidence offers this receptor as an attractive therapeutic target: selective CB₂ agonists are able to modulate inflammation without triggering psychotropic effects. In this work, we report a new series of selective CB₂ agonists based on a benzo[d]thiazol-2(3H)-one scaffold. This drug design project led to the discovery of compound 9, as a very potent CB₂ agonist (K_i = 13.5 nM) with a good selectivity versus CB₁. This compound showed no cytotoxicity, acceptable ADME-Tox parameters and demonstrates the ability to counteract colon inflammatory process in vivo.

A study on the reaction of 3-alkyl(aryl)imidazo[1,5-a]pyridines with ninhydrin

The reaction of 3-alkyl(aryl)imidazo[1,5-a]pyridines (1) with ninhydrin in dichloromethane at room temperature delivered good yields of the respective 2-hydroxy-2-(imidazo[1,5-a]pyridine-1-yl)indene-1,3-diones. In the presence of dimethyl acetylenedicarboxylate (DMAD), this uncatalyzed electrophilic substitution reaction, involving C-1 (in 1) and the central C=O (in ninhydrin), takes precedence over the three-component 1,4-dipolar cycloaddition reaction. This selectivity is probably due to the higher electrophilicity of the carbonyl carbon-2 in ninhydrin as compared to that of the sp-carbon atoms in DMAD, augmented with the high nucleophilicity of carbon-1 in 1.

Multicomponent Reaction Based Synthesis of 1-Tetrazolylimidazo[1,5- a]pyridines

A series of unprecedented tetrazole-linked imidazo[1,5-a]pyridines are synthesized from simple and readily available building blocks. The reaction sequence involves an azido-Ugi-deprotection reaction followed by an acetic anhydride-mediated N-acylation–cyclization process to afford the target heterocycle. Furthermore, the scope of the methodology was extended to diverse R₃-substitutions by employing commercial anhydrides, acid chlorides, and acids as an acyl component. The scope for the postmodification reactions are explored and the usefulness of the synthesis is exemplified by an improved three-step synthesis of a guanylate cyclase stimulator.

Structure-Activity Relationship of Cannabis Derived Compounds for the Treatment of Neuronal Activity-Related Diseases

Cannabis sativa active compounds are extensively studied for their therapeutic effects, beyond the well-known psychotropic activity. C. Sativa is used to treat different medical indications, such as multiple sclerosis, spasticity, epilepsy, ulcerative colitis and pain. Simultaneously, basic research is discovering new constituents of cannabis-derived compounds and their receptors capable of neuroprotection and neuronal activity modulation. The function of the various phytochemicals in different therapeutic processes is not fully understood, but their significant role is starting to emerge and be appreciated. In this review, we will consider the structure-activity relationship (SAR) of cannabinoid compounds able to bind to cannabinoid receptors and act as therapeutic agents in neuronal diseases, e.g., Parkinson’s disease.

Perspectives of Cannabinoid Type 2 Receptor (CB2R) Ligands in Neurodegenerative Disorders: Structure-Affinity Relationship (SAfiR) and Structure-Activity Relationship (SAR) Studies

Up-regulation of CB2R on activated microglial cells, the first step in neurodegeneration, has been widely demonstrated, and this finding makes the receptor a promising target in the early diagnosis and treatment of several neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and multiple sclerosis (MS). The development of CB2R PET ligands could help demonstrate the neurodegenerative pathogenesis, thus providing useful tools for characterizing the role of neuroinflammation in the progression of these disorders. CB2R agonists and inverse agonists have emerged as neuroprotective agents, and CB2R agonists have entered several clinical trials. CB2R ligands have therefore received great attention, and different molecular scaffolds have been selected to target CB2R subtypes. This review is focused on structure-activity relationship (SAR) and structure-affinity relationship (SAfiR) studies performed on different scaffolds with the aim to identify the molecular features useful for the design of both therapeutic and diagnostic agents.

The Impact of Chemical Probes in Drug Discovery: A Pharmaceutical Industry Perspective

Chemical probes represent an important component of both academic and pharmaceutical drug discovery research. As a complement to prior reviews that have defined this scientific field, we aim to provide an industry perspective on the value of having high-quality chemical probes throughout the course of preclinical research. By studying examples from the internal Merck pipeline, we recognize that these probes require significant collaborative investment to realize their potential impact in clarifying the tractability and translation of a given therapeutic target. This perspective concludes with recommendations for chemical probe discovery aimed toward maximizing their potential to identify targets that result in the successful delivery of novel therapeutics.

Copper-mediated C(sp3)–H amination in a multiple C–N bond-forming strategy for the synthesis of N-heterocycles

A three-component reaction for the construction of imidazo[1,5-a]pyridines through copper-promoted C(sp³)–H amination has been developed.

N-Bridged 5,6-bicyclic pyridines: Recent applications in central nervous system disorders

The search for novel heterobicyclic compounds within the drug-like chemical space continues to be an area of interest in medicinal chemistry. Unsaturated N-bridgehead heterocycles are well represented in marketed drugs for a variety of therapeutic areas, and continue to play an important role in central nervous system (CNS) drug discovery programs. Examples of medicinal chemistry strategies that make use of N-bridged 5,6-bicyclic pyridines are discussed here in this Minireview, which covers the literature from 2010 up to 2014. B1-class imidazopyridines and B3-class pyrazolopyridines have proven to be at the forefront of molecular prototypes that are capable of interacting with disease relevant targets in neurodegeneration and neuropsychiatry.

Selective cannabinoid receptor type 2 (CB2) agonists: optimization of a series of purines leading to the identification of a clinical candidate for the treatment of osteoarthritic pain

A focused screening strategy identified thienopyrimidine 12 as a cannabinoid receptor type 2 agonist (hCB2) with moderate selectivity over the hCB1 receptor. This initial hit suffered from poor in vitro metabolic stability and high in vivo clearance. Structure-activity relationships describe the optimization and modification to a new more polar series of purine CB2 agonists. Examples from this novel scaffold were found to be highly potent and fully efficacious agonists of the human CB2 receptor with excellent selectivity against CB1, often having no CB1 agonist activity at the highest concentration measured (>100 μM). Compound 26 is a centrally penetrant molecule which possesses good biopharmaceutical properties, is highly water-soluble, and demonstrates robust oral activity in rodent models of joint pain. In addition, the peripherally restricted molecule 22 also demonstrated significant efficacy in the same analgesic model of rodent inflammatory pain.

Analgesic effect of a mixed T-type channel inhibitor/CB2 receptor agonist

BACKGROUND

Cannabinoid receptors and T-type calcium channels are potential targets for treating pain. Here we report on the design, synthesis and analgesic properties of a new mixed cannabinoid/T-type channel ligand, NMP-181.

RESULTS

NMP-181 action on CB1 and CB2 receptors was characterized in radioligand binding and in vitro GTPγ[35S] functional assays, and block of transiently expressed human Cav3.2 T-type channels by NMP-181 was analyzed by patch clamp. The analgesic effects and in vivo mechanism of action of NMP-181 delivered spinally or systemically were analyzed in formalin and CFA mouse models of pain. NMP-181 inhibited peak CaV3.2 currents with IC50 values in the low micromolar range and acted as a CB2 agonist. Inactivated state dependence further augmented the inhibitory action of NMP-181. NMP-181 produced a dose-dependent antinociceptive effect when administered either spinally or systemically in both phases of the formalin test. Both i.t. and i.p. treatment of mice with NMP-181 reversed the mechanical hyperalgesia induced by CFA injection. NMP-181 showed no antinocieptive effect in CaV3.2 null mice. The antinociceptive effect of intrathecally delivered NMP-181 in the formalin test was reversed by i.t. treatment of mice with AM-630 (CB2 antagonist). In contrast, the NMP-181-induced antinociception was not affected by treatment of mice with AM-281 (CB1 antagonist).

CONCLUSIONS

Our work shows that both T-type channels as well as CB2 receptors play a role in the antinociceptive action of NMP-181, and also provides a novel avenue for suppressing chronic pain through novel mixed T-type/cannabinoid receptor ligands.

Membrane phospholipid bilayer as a determinant of monoacylglycerol lipase kinetic profile and conformational repertoire

The membrane-associated serine hydrolase, monoacylglycerol lipase (MGL), is a well-recognized therapeutic target that regulates endocannabinoid signaling. Crystallographic studies, while providing structural information about static MGL states, offer no direct experimental insight into the impact of MGL's membrane association upon its structure-function landscape. We report application of phospholipid bilayer nanodiscs as biomembrane models with which to evaluate the effect of a membrane system on the catalytic properties and conformational dynamics of human MGL (hMGL). Anionic and charge-neutral phospholipid bilayer nanodiscs enhanced hMGL's kinetic properties [apparent maximum velocity (Vmax) and substrate affinity (Km)]. Hydrogen exchange mass spectrometry (HX MS) was used as a conformational analysis method to profile experimentally the extent of hMGL-nanodisc interaction and its impact upon hMGL structure. We provide evidence that significant regions of hMGL lid-domain helix α4 and neighboring helix α6 interact with the nanodisc phospholipid bilayer, anchoring hMGL in a more open conformation to facilitate ligand access to the enzyme's substrate-binding channel. Covalent modification of membrane-associated hMGL by the irreversible carbamate inhibitor, AM6580, shielded the active site region, but did not increase solvent exposure of the lid domain, suggesting that the inactive, carbamylated enzyme remains intact and membrane associated. Molecular dynamics simulations generated conformational models congruent with the open, membrane-associated topology of active and inhibited, covalently-modified hMGL. Our data indicate that hMGL interaction with a phospholipid membrane bilayer induces regional changes in the enzyme's conformation that favor its recruiting lipophilic substrate/inhibitor from membrane stores to the active site via the lid, resulting in enhanced hMGL catalytic activity and substrate affinity.

Triflic anhydride mediated synthesis of imidazo[1,5-a]azines

Imidazo[1,5-a]azines are synthesized in moderate to excellent yields using a mild cyclodehydration/aromatization reaction triggered by the use of triflic anhydride (Tf2O) and 2-methoxypyridine (2-MeOPyr). Various substitution patterns and functional groups were found to be compatible under the optimized conditions. In addition, a 5-bromo-3-aryl derivative was also shown to be active in a Sonogashira cross-coupling and direct arylation reactions. A tertiary amide was compatible as a substrate leading to the synthesis of an imidazo[1,5-a]pyridinium triflate.

Design, synthesis, binding and docking-based 3D-QSAR studies of 2-pyridylbenzimidazoles--a new family of high affinity CB1 cannabinoid ligands

A series of novel 2-pyridylbenzimidazole derivatives was rationally designed and synthesized based on our previous studies on benzimidazole 14, a CB1 agonist used as a template for optimization. In the present series, 21 compounds displayed high affinities with K_i values in the nanomolar range. JM-39 (compound 39) was the most active of the series (K_iCB1 = 0.53 nM), while compounds 31 and 44 exhibited similar affinities to WIN 55212-2. CoMFA analysis was performed based on the biological data obtained and resulted in a statistically significant CoMFA model with high predictive value (q² = 0.710, r² = 0.998, r²_pred = 0.823).

Recent Advances in Selective CB2 Agonists for the Treatment of Pain

The cannabinoid CB2 receptor is one of a family of GPCRs that mediate the effects of endocannabinoids. Several agonists of this receptor are currently in clinical trials for the treatment of pain and inflammation, indications that have been validated by pre-clinical studies on agonists and in receptor knockout mice. Key to the clinical advancement of CB2 agonists is achieving selectivity over the related CB1 receptor, whose activation results in undesirable CNS effects, limiting therapeutic utility. A variety of CB2 receptor agonist chemotypes are reviewed including mono-, bi- and tricyclic cores and bi- and triaryl cores. Pharmacology, with a focus on selectivity requirements and a variety of pre-clinical animal models to assess activity and selectivity, is presented.

Imidazo[1,5-a]pyridine-1-ylalkylalcohols: synthesis via intramolecular cyclization of N-thioacyl 1,2-aminoalcohols and their silyl ethers and molecular structures

Iodine-mediated cyclization of N-thioacyl 1,2-aminoalcohols derived from aromatic aldehydes and ketones mainly produced bis(1-imidazo[1,5-a]pyridyl)arylmethanes, whereas the reaction of N-thioacyl 1,2-aminoalcohols derived from aliphatic aldehydes and N-thioacyl 1,2-aminoalcohols protected with a silyl group with iodine gave imidazo[1,5-a]pyridine-1-ylalkylalcohols as a major product.

Latest advances in novel cannabinoid CB(2) ligands for drug abuse and their therapeutic potential

The field of cannabinoid (CB) drug research is experiencing a challenge as the CB(1) antagonist Rimonabant, launched in 2006 as an anorectic/anti-obesity drug, was withdrawn from the European market due to the complications of suicide and depression as side effects. There is interest in developing CB(2) drugs without CB(1) psychotropic side effects for drug-abuse treatment and therapeutic medication. The CB(1) receptor was discovered predominantly in the brain, whereas the CB(2) is mainly expressed in peripheral cells and tissues, and is involved in immune signal transduction. Conversely, the CB(2) receptor was recently detected in the CNS, for example, in the microglial cells and the neurons. While the CB(2) neurons activity remains controversial, the CB(2) receptor is an attractive therapeutic target for neuropathic pain, immune system, cancer and osteoporosis without psychoactivity. This review addresses CB drug abuse and therapeutic potential with a focus on the most recent advances on new CB(2) ligands from the literature as well as patents.

5-sulfonyl-benzimidazoles as selective CB2 agonists-part 2

In a previous communication, the SAR of a series of potent and selective 5-sulfonyl-benzimidazole CB2-receptor agonists was described. The lack of in vivo activity of compounds from this series was attributed to their poor solubility and metabolic stability. In this Letter, we report on the further optimization of this series, leading to the relatively polar and peripherically acting CB2 agonists 41 and 49. Although both compounds were not active in acute pain models, the less selective compound 41 displayed good, sustained activity in a chronic model of neuropathic pain without the tolerance observed with morphine. In addition, both 41 and 49 delayed the onset of clinical symptoms in an experimental model for Multiple sclerosis.

Discovery and optimization of 1-(4-(pyridin-2-yl)benzyl)imidazolidine-2,4-dione derivatives as a novel class of selective cannabinoid CB2 receptor agonists

Here, we report the identification and optimization of 1-(4-(pyridin-2-yl)benzyl)imidazolidine-2,4-dione derivatives as a novel chemotype with selective cannabinoid CB2 receptor agonist activity. 1 is a potent and selective cannabinoid CB2 receptor agonist (hCB2 pEC(50) = 8.6). The compound was found to be metabolically unstable, which resulted in low oral bioavailability in rat (F(po) = 4%) and possessed off-target activity at the hERG ion channel (pK(i) = 5.5). Systematic modification of physicochemical properties, such as lipophilicity and basicity, was used to optimize the pharmacokinetic profile and hERG affinity of this novel class of cannabinoid CB2 receptor agonists. This led to the identification of 44 as a potent, selective, and orally bioavailable cannabinoid CB2 receptor agonist (hCB2 pEC(50) = 8.0; hERG pK(i) < 4; F(po) = 100%), which was active in a rat spinal nerve ligation model of neuropathic pain.