Design,synthesis, and structure–activity relationship study of conformationally constrained analogs of indole-3-carboxamides as novel CB1 cannabinoid receptor agonists

Novel tricyclic indole-3-carboxamides were synthesized as structurally restricted analogs of bicyclic indoles, and found to be potent CB1 cannabinoid receptor agonists. The CB1 agonist activity depended on the absolute configuration of the chiral center of the tricyclic ring. The preferred enantiomer was more potent than the structurally unconstrained lead compound. Structure–activity relationships in the amide side chain of the indole C-3 position were also investigated.     

2-Arylimino-5,6-dihydro-4H-1,3-thiazines as a new class of cannabinoid receptor agonists. Part 3: Synthesis and activity of isosteric analogs

Structure-activity relationships and efforts to optimize the pharmacokinetic profile of isosteric analogs of 2-arylimino-5,6-dihydro-4H-1,3-thiazines as cannabinoid receptor agonists are described. Among those examined, compound 25 showed potent affinity for cannabinoid receptor 1 (CB1) and receptor 2 (CB2). This compound displayed oral bioavailability and analgesic activity.     

Synthesis of bicyclic thiazolidine PAF antagonists

PAF antagonist 1 is susceptible to thiazolidine ring fragmentation in vitro and in vivo. The search for a more stable compound prompted the synthesis of a series of bicyclic analogs. Three classes of bicyclic thiazolidines (2: X = 0, CH₂, NCH₃) were prepared using a common synthetic pathway which generated all the possible diastereomers. The most potent PAF antagonists were the oxygen-substituted analogs which possessed receptor binding affinities largely dependent on stereochemistry.     

Synthesis and cannabinoid-1 receptor binding affinity of conformationally constrained analogs of taranabant

The design, synthesis, and binding activity of ring constrained analogs of the acyclic cannabinoid-1 receptor (CB1R) inverse agonist taranabant 1 are described. The initial inspiration for these taranabant derivatives was its conformation 1a, determined by ¹H NMR, X-ray, and molecular modeling. The constrained analogs were all much less potent than their acyclic parent structure. The results obtained are discussed in the context of a predicted binding of 1 to a homology model of CB1R.     

Discovery of novel isothiazole inhibitors of the TrkA kinase: structure-activity relationship, computer modeling, optimization, and identification of highly potent antagonists

The design, synthesis, and biological evaluation of potent inhibitors of the TrkA kinase is presented. A homology model is created to aid in the enhancement of potency and selectivity of isothiazole inhibitors found during a high-throughput screen. Three different syntheses are utilized to make diverse analogs within this series. Aminoheterocycles are found to be good urea surrogates, whereas bicyclic substituents on the C3 thio group were found to be extremely potent TrkA inhibitors in kinase and cell assays.     

Structure-activity relationships of 2,4-diphenyl-1H-imidazole analogs as CB2 receptor agonists for the treatment of chronic pain

A series of 2,4-diphenyl-1H-imidazole analogs have been synthesized and displayed potent human CB2 agonist activity. Many of these analogs showed high functional selectivity over human CB1 receptors. The syntheses, structure-activity relationships, and selected pharmacokinetic data of these analogs are described.     

Potent inhibition of macrophomate synthase by reaction intermediate analogs

Potent inhibitors for macrophomate synthase, which has recently been found to catalyze a highly unusual five-step chemical transformation, were explored. Among 11 oxalacetate analogs tested, only three analogs had moderate to relatively strong inhibitory activities (I50 1.3-8.1 mM). On the other hand, among 35 bicyclic intermediate analogs synthesized, two diacids were found to be the most potent inhibitors (I50 0.80, 0.84 mM) which had a much higher affinity than that of the natural substrate 2-pyrone. (-)-Enantiomers of the diacids showed 30 times stronger activity (I50 0.34, 0.41 mM) than (+)-ones. The I50/Km values (0.20, 0.24) showed their potent inhibitions. Competitive inhibitions were observed in two representative inhibitors.     

Low brain penetrant CB1 receptor agonists for the treatment of neuropathic pain

Novel, low brain penetrant, orally bioavailable CB1 receptor agonists were designed starting from a mature lead series of potent brain penetrant CB1 receptor agonists. Increasing the calculated polar surface area was found to be a good strategy for reducing brain penetration whilst retaining drug-like properties. This in silico approach led to the discovery of LBP1, an orally bioavailable, low brain penetrant CB1 receptor agonist with robust activity in rodent models of neuropathic pain and a good preclinical therapeutic profile, which was selected for clinical development.     

Microwave-assisted synthesis of quinoline, isoquinoline, quinoxaline and quinazoline derivatives as CB2 receptor agonists

Quinoline, isoquinoline, quinoxaline, and quinazoline derivatives were synthesized using microwave-assisted synthesis and their CB1/CB2 receptor activities were determined using the [3?S]GTPγS binding assay. Most of the prepared quinoline, isoquinoline, and quinoxalinyl phenyl amines showed low-potency partial CB2 receptor agonists activity. The most potent CB2 ligand was the 4-morpholinylmethanone derivative (compound 40e) (-log EC?? = 7.8; E(max) = 75%). The isoquinolin-1-yl(3-trifluoromethyl-phenyl)amine (compound 26c) was a high efficacy CB2 agonist (-log EC?? = 5.8; E(max) = 128%). No significant CB1 receptor activation or inactivation was shown in these studies, except 40e, which showed weak CB1 agonist activity (CB1 -log EC?? = 5.0). These ligands serve as novel templates for the development of selective CB2 receptor agonist.     

Discovery of potent and orally bioavailable heterocycle-based cannabinoid CB1 receptor agonists

Novel 3-(1H-indol-3-yl)-1,2,4-oxadiazoles and -thiadiazoles were synthesized and found to be potent CB1 cannabinoid receptor agonists. The oral bioavailability of these compounds could be dramatically improved by optimization studies of the side chains attached to the indole and oxadiazole cores, leading to identification of a CB1 receptor agonist with good oral activity in a range of preclinical models of antinociception and antihyperalgesia.     

Synthesis and evaluation of CCR5 antagonists containing modified 4-piperidinyl-2-phenyl-1-(phenylsulfonylamino)-butane

Synthesis of analogs containing more rigid bicyclic piperidine replacements for the 4-benzyloxycarbonyl-(ethyl)amino-piperidine moiety of the CCR5 antagonist structure, 1, is described. Although similar binding affinity to the lead was achieved with some analogs they were overall less potent anti-HIV agents suggesting that other features besides CCR5 binding are required for good anti-viral activity.     

Peri-substituted hexahydro-indolones as novel,potent and selective human EP3 receptor antagonists

A series of peri-substituted [4.3.0] bicyclic non-aromatic heterocycles have been identified as potent and selective hEP₃ receptor antagonists. These molecules adopt a hair-pin conformation that overlaps with the endogenous ligand PGE₂ and fits into an internally generated EP₃ pharmacophore model. Optimized compounds show good metabolic stability and improved solubility over their corresponding bicyclic aromatic analogs.     

7-Azaindolequinuclidinones (7-AIQD): A novel class of cannabinoid 1 (CB1) and cannabinoid 2 (CB2) receptor ligands

A series of N-benzyl-7-azaindolequinuclidinone (7-AIQD) analogs have been synthesized and evaluated for affinity toward CB1 and CB2 cannabinoid receptors and identified as a novel class of cannabinoid receptor ligands. Structure–activity relationship (SAR) studies indicate that 7-AIQD analogs are dual CB1/CB2 receptor ligands exhibiting high potency with somewhat greater selectivity towards CB2 receptors compared to the previously reported indolequinuclidinone (IQD) analogs. Initial binding assays showed that 7-AIQD analogs 8b, 8d, 8f, 8g and 9b (1 μM) produced more that 50% displacement of the CB1/CB2 non-selective agonist CP-55,940 (0.1 nM). Furthermore, Ki values determined from full competition binding curves showed that analogs 8a, 8b and 8g exhibit high affinity (110, 115 and 23.7 nM, respectively) and moderate selectivity (26.3, 6.1 and 9.2-fold, respectively) for CB2 relative to CB1 receptors. Functional studies examining modulation of G-protein activity demonstrated that 8a acts as a neutral antagonist at CB1 and CB2 receptors, while 8b exhibits inverse agonist activity at these receptors. Analogs 8f and 8g exhibit different intrinsic activities, depending on the receptor examined. Molecular docking and binding free energy calculations for the most active compounds (8a, 8b, 8f, and 8g) were performed to better understand the CB2 receptor-selective mechanism at the atomic level. Compound 8g exhibited the highest predicted binding affinity at both CB1 and CB2 receptors, and all four compounds were shown to have higher predicted binding affinities with the CB2 receptor compared to their corresponding binding affinities with the CB1 receptor. Further structural optimization of 7-AIQD analogs may lead to the identification of potential clinical agents.     

Discovery and optimization of potent broad-spectrum arenavirus inhibitors derived from benzimidazole and related heterocycles

A series of potent arenavirus inhibitors sharing a benzimidazole core were previously reported by our group. SAR studies were expanded beyond the previous analysis, which involved the attached phenyl rings and methylamino linker portion, to include modifications focused on the benzimidazole core. These changes included the introduction of various substituents to the bicyclic benzimidazole ring system along with alternate core heterocycles. Many of the analogs containing alternate nitrogen-based bicyclic ring systems were found to retain antiviral potency compared to the benzimidazole series from which we derived our lead compound, ST-193. In fact, 21h, built on an imidazopyridine core, possessed a near tenfold increase in potency against Lassa virus pseudotypes compared to ST-193. As found with the benzimidazole series, broad-spectrum arenavirus activity was also observed for a number of the analogs discovered during this study.     

Discovery and optimization of novel purines as potent and selective CB2 agonists

A focused screening strategy identified thienopyrimidine 1 as a hCB2 cannabinoid receptor agonist 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 less lipophilic purine core. Examples from this novel series were found to be highly potent and fully efficacious agonists of the human CB2 receptor with excellent selectivity against CB1. Compound 10 possesses good biopharmaceutical properties, is highly water soluble and demonstrates robust oral activity in rodent models of joint pain.     

Different pharmacological profile of two closely related endocannabinoid ester analogs

The pharmacological and neuroprotective properties of two ester analogs of the endocannabinoids, arachidonoylethyleneglycol (AA-EG) and alpha,alpha,-dimethyl arachidonoylethyleneglycol (DMA-EG), were investigated. We examined the interaction of both compounds with cannabinoid receptors (CB1 and CB2) and their efficacy in functional assays. In competition binding assays, AA-EG and DMA-EG had low potency to displace the CB1/CB2 agonist [3H]CP-55,940 in membrane preparations expressing rodent or human receptors. Binding data correlate with low efficacy of both compounds as regards to inhibition of adenylyl cyclase activity. It was also shown that DMA-EG resists hydrolysis by rat brain membranes while AA-EG undergo complete splitting under these conditions. In the cannabinoid tetrad, AA-EG induced hypomotility, analgesia, catalepsy and decreased rectal temperature indicating cannabimimetic activity. By contrast, DMA-EG was completely inactive in the same models. DMA-EG and AA-EG potently protected rat cortical neurons in culture against oxygen deprivation at nanomolar concentrations. In glutamate-induced damage, the compounds were less active protecting neurons at micromolar concentrations. The data obtained indicate that the ester endocannabinoid template can be used for the development of new compounds with potent biological activity lacking some of the undesirable behavioral side effects.     

Design, synthesis and biological evaluation of piperazine analogues as CB1 cannabinoid receptor ligands

After the CB1 receptor antagonist SR141716 (rimonabant) was previously reported to modulate food intake, CB1 antagonism has been considered as a new therapeutic target for the treatment of obesity. Several series of urea, carbamate, amide, sulfonamide and oxalamide derivatives based on 1-benzhydrylpiperazine scaffold were synthesized and tested for CB1 receptor binding affinity. The SAR studies to optimize the CB1 binding affinity led to the potent urea derivatives. After the additional SAR studies to optimize the substituents of diphenyl rings, the combination of 2-chlorophenyl and 4-chlorophenyl turned out to be the most potent scaffold. The CB2 binding affinity assay as well as functional assay was also conducted on these compounds. Herein we wish to introduce several novel CB1 antagonists with IC(50) values less than 100 nM for the CB1 receptor binding.     

Design, synthesis and evaluation of bicyclic benzamides as novel 5-HT1F receptor agonists

Several fused bicyclic systems have been investigated to serve as the core structure of potent and selective 5-HT_1F receptor agonists. Replacement of the indole nucleus in 2 with indazole and ‘inverted’ indazole provided more potent and selective 5-HT_1F receptor ligands. Indoline and 1,2-benzisoxazole systems also provided potent 5-HT_1F receptor agonists, and the 5-HT_1A receptor selectivity of the indoline- and 1,2-benzisoxazole-based 5-HT_1F receptor agonists could be improved with modification of the benzoyl moiety of the benzamides. Through these studies, we found that the inherent geometries of the templates, not the nature of hybridization of the linking atom, were important for the 5-HT_1F receptor recognition.     

Synthesis and evaluation of 3-aryl piperidine analogs as potent and efficacious dopamine D4 receptor agonists

A series of 3-aryl piperidine analogs with 2-piperidinoalkylamino or 2-piperidinoalkyloxy fused bicyclic rings were prepared and found to be potent and efficacious human dopamine D4 agonists. The synthesis and structure-activity relationship (SAR) studies that led to the identification of these compounds are discussed.     

Selective CB2 agonists with anti-pruritic activity: Discovery of potent and orally available bicyclic 2-pyridones

The CB2 receptor has emerged as a potential target for the treatment of pruritus as well as pain without CB1-mediated side effects. We previously identified 2-pyridone derivatives 1 and 2 as potent CB2 agonists; however, this series of compounds was found to have unacceptable pharmacokinetic profiles with no significant effect in vivo. To improve these profiles, we performed further structural optimization of 1 and 2, which led to the discovery of bicyclic 2-pyridone 18e with improved CB2 affinity and selectivity over CB1. In a mouse pruritus model, 18e inhibited compound 48/80 induced scratching behavior at a dose of 100 mg/kg. In addition, the docking model of 18e with an active-state CB2 homology model indicated the structural basis of its high affinity and selectivity over CB1.