Pyrazole antagonists of the CB1 receptor with reduced brain penetration

Type 1 cannabinoid receptor (CB1) antagonists might be useful for treating obesity, liver disease, metabolic syndrome, and dyslipidemias. Unfortunately, inhibition of CB1 in the central nervous system (CNS) produces adverse effects, including depression, anxiety and suicidal ideation in some patients, which led to withdrawal of the pyrazole inverse agonist rimonabant (SR141716A) from European markets. Efforts are underway to produce peripherally selective CB1 antagonists to circumvent CNS-associated adverse effects. In this study, novel analogs of rimonabant (1) were explored in which the 1-aminopiperidine group was switched to a 4-aminopiperidine, attached at the 4-amino position (5). The piperidine nitrogen was functionalized with carbamates, amides, and sulfonamides, providing compounds that are potent inverse agonists of hCB1 with good selectivity for hCB1 over hCB2. Select compounds were further studied using in vitro models of brain penetration, oral absorption and metabolic stability. Several compounds were identified with predicted minimal brain penetration and good metabolic stability. In vivo pharmacokinetic testing revealed that inverse agonist 8c is orally bioavailable and has vastly reduced brain penetration compared to rimonabant.     

JD-5006 and JD-5037: Peripherally restricted (PR) cannabinoid-1 receptor blockers related to SLV-319 (Ibipinabant) as metabolic disorder therapeutics devoid of CNS liabilities

Analogs of SLV-319 (Ibipinibant), a CB1 receptor inverse agonist, were synthesized with functionality intended to limit brain exposure while maintaining the receptor affinity and selectivity of the parent compound. Structure activity relationships of this series, and pharmacology of two lead compounds, 16 (JD-5006) and 23 (JD-5037) showing little brain presence as indicated by tissue distribution and receptor occupancy studies, are described. Effects with one of these compounds on plasma triglyceride levels, liver weight and enzymes, glucose tolerance and insulin sensitivity support the approach that blockade of peripheral CB₁ receptors is sufficient to produce many of the beneficial metabolic effects of globally active CB₁ blockers. Thus, PR CB₁ inverse agonists may indeed represent a safer alternative to highly brain-penetrant agents for the treatment of metabolic disorders, including diabetes, liver diseases, dyslipidemias, and obesity.     

Synthesis and pharmacological characterization of functionalized 6-piperazin-1-yl-purines as cannabinoid receptor 1 (CB1) inverse agonists

Antagonists of peripheral type 1 cannabinoid receptors (CB1) may have utility in the treatment of obesity, liver disease, metabolic syndrome and dyslipidemias. We have targeted analogues of the purine inverse agonist otenabant (1) for this purpose. The non-tissue selective CB1 antagonist rimonabant (2) was approved as a weight-loss agent in Europe but produced centrally mediated adverse effects in some patients including dysphoria and suicidal ideation leading to its withdrawal. Efforts are now underway to produce compounds with limited brain exposure. While many structure-activity relationship (SAR) studies of 2 have been reported, along with peripheralized compounds, 1 remains relatively less studied. In this report, we pursued analogues of 1 in which the 4-aminopiperidine group was switched to piperazine group to enable a better understanding of SAR to eventually produce compounds with limited brain penetration. To access a binding pocket and modulate physical properties, the piperazine was functionalized with alkyl, heteroalkyl, aryl and heteroaryl groups using a variety of connectors, including amides, sulfonamides, carbamates and ureas. These studies resulted in compounds that are potent antagonists of hCB1 with high selectivity for hCB1 over hCB2. The SAR obtained led to the discovery of 65 (Ki?=?4?nM, >1,000-fold selective for hCB1 over hCB2), an orally bioavailable aryl urea with reduced brain penetration, and provides direction for discovering peripherally restricted compounds with good in vitro and in vivo properties.     

The discovery of novel 3-aryl-indazole derivatives as peripherally restricted pan-Trk inhibitors for the treatment of pain

The design, synthesis, and biological evaluation of novel 3-aryl-indazole derivatives as peripherally selective pan-Trk inhibitors are described. Three strategies were used to obtain a potent compound exhibiting low central nervous system (CNS) penetration and high plasma exposure: 1) a structure-based drug design (SBDD) approach was used to improve potency; 2) a substrate for an efflux transporter for lowering brain penetration was explored; and 3) the most basic pKa (pKa–MB) value was used as an indicator to identify compounds with good membrane permeability. This enabled the identification of the peripherally targeted 17c with the potency, kinase-selectivity, and plasma exposure required to demonstrate in vivo efficacy in a Complete Freund's adjuvant (CFA)-induced thermal hypersensitivity model.     

Fluorine-18 isotope labeling for positron emission tomography imaging. Direct evidence for DBPR211 as a peripherally restricted CB1 inverse agonist

The [¹⁸F] isotope-labelled CB1 inverse agonist 3 was elaborated and synthesized for positron emission tomography scanning studies. After immediate purification and calibration with its unlabeled counterpart, compound 3 was intravenously injected in mice and revealed that its distribution percentage in brain over 90-min scans among five region of interests, including brain, liver, heart, thigh muscle and kidney was lower than 1%, thus providing direct evidence to justify itself as a peripherally restricted CB1 antagonist.     

Carbon-11 N-methyl alkylation of L-368,899 and in vivo PET imaging investigations for neural oxytocin receptors

Compound L-368,899 was successfully alkylated with [¹¹C]iodomethane to generate the oxytocin receptor selective (2R)-2-amino-N-((2S)-7,7-dimethyl-1-(((4-(o-tolyl)piperazin-1-yl)sulfonyl)methyl)bicyclo[2.2.1]heptan-2-yl)-N-[¹¹C]methyl-3-(methylsulfonyl)propanamide ([¹¹C]1) with very high radiochemical purity and high specific activity. PET imaging studies were performed with [¹¹C]1 to investigate brain penetration and oxytocin receptor uptake using rat and cynomolgus monkey models. For rat baseline scans, brain penetration was observed with [¹¹C]1, but no specific uptake could be distinguished in the brain region. By administering a peptide oxytocin receptor selective antagonist for peripheral blocking of oxytocin receptors, the uptake of [¹¹C]1 was amplified in the rat brain temporarily to enable some visual uptake within the rat brain. A baseline scan of [¹¹C]1 in a cynomolgus monkey model resulted in no detectable specific uptake in anticipated regions, but activity did accumulate in the choroid plexus.     

Pyrido[2,3-b]pyrazines,discovery of TRPV1 antagonists with reduced potential for the formation of reactive metabolites

The transient receptor potential cation channel, subfamily V, member 1 (TRPV1) is a non-selective cation channel that can be activated by a wide range of noxious stimuli, including capsaicin, acid, and heat. Blockade of TRPV1 activation by selective antagonists is under investigation in an attempt to identify novel agents for pain treatment. During pre-clinical development, the 1,8-naphthyridine 2 demonstrated unacceptably high levels of irreversible covalent binding. Replacement of the 1,8-naphthyridine core by a pyrido[2,3-b]pyrazine led to the discovery of compound 26 which was shown to have significantly lower potential for the formation of reactive metabolites. Compound 26 was characterized as an orally bioavailable TRPV1 antagonist with moderate brain penetration. In vivo, 26 significantly attenuated carrageenan-induced thermal hyperalgesia (CITH) and dose-dependently reduced complete Freund’s adjuvant (CFA)-induced chronic inflammatory pain after oral administration.     

Synthesis and SAR of heterocyclic carboxylic acid isosteres based on 2-biarylethylimidazole as bombesin receptor subtype-3 (BRS-3) agonists for the treatment of obesity

SAR around non-peptidic potent bombesin receptor subtype-3 (BRS-3) agonist lead 2 is presented. Attempts to replace the carboxylic acid with heterocyclic isosteres to improve oral bioavailability and brain penetration are described.     

Synthesis and optimization of 4,5,6,7-tetrahydrooxazolo[4,5-c]pyridines as potent and orally-active metabotropic glutamate receptor 5 negative allosteric modulators

We describe here the design, synthesis and characterization of a series of 4,5,6,7-tetrahydrooxazolo[4,5-c]pyridines as metabotropic glutamate receptor (mGluR) 5 negative allosteric modulators (NAMs). Optimization of the substituents led to the identification of several compounds with good pharmacokinetic profiles, including long half life and high oral bioavailability, in both rats and monkeys. The receptor occupancy test in the rat cortex revealed favorable brain penetration of these compounds. The reprsentative compound 13 produced oral antidepressant-like effect in the rat forced swimming test (MED: 0.3 mg/kg, q.d.).     

Synthesis and SAR of novel quinazolines as potent and brain-penetrant c-jun N-terminal kinase (JNK) inhibitors

Quinazoline 3 was discovered as a novel c-jun N-terminal kinase (JNK) inhibitor with good brain penetration and pharmacokinetic (PK) properties. A number of analogs which were potent both in the biochemical and cellular assays were discovered. Quinazoline 13a was found to be a potent JNK3 inhibitor (IC₅₀ = 40 nM), with >500-fold selectivity over p38, and had good PK and brain penetration properties. With these properties, 13a is considered a potential candidate for in vivo evaluation.     

Homoisoflavonoids from the inter-bulb surfaces of Scilla nervosa subsp. rigidifolia

Eight homoisoflavonoids, two of which are new: 3-(4′-methoxybenzyl)-5,6,7-trimethoxychroman-4-one (1); 3-(4′-methoxybenzyl)-5,7-dimethoxychroman-4-one (2); 3-(4′-methoxybenzyl)-7-hydroxy-5,6-dimethoxychroman-4-one (3); 3-(4′-methoxybenzyl)-6-hydroxy-5,7-dimethoxychroman-4-one (4); 3-(3′-hydroxy-4′-methoxybenzyl)-5,7-dihydroxy-6-methoxychroman-4-one (5); 3-(3′-hydroxy-4′-methoxybenzyl)-5,7-dihydroxychroman-4-one (6); 3-(4′-hydroxybenzylidene)-5,7-dihydroxy-6-methoxychroman-4-one (7) and 3-(4′-hydroxybenzylidene)-5,7-dihydroxychroman-4-one (8), were isolated from the yellow Inter-bulb deposits from Scilla nervosa. The structures of these compounds were elucidated and characterized by 1D- and 2D-NMR and mass spectrometry. The structures of the known compounds were compared to those ones in literature.     

Synthesis and biological evaluation of Esaprazole analogues showing σ1 binding and neuroprotective properties in vitro

Esaprazole, a molecule previously acknowledged to protect against stomach and intestinal ulcers was surprisingly discovered to have neuroprotective activities and σ₁ binding in vitro. A highly diverse set of Esaprazole analogues 2–5 was prepared in order to increase blood–brain barrier penetration. The analogues showed a structure–activity relationship at the σ₁ receptor closely matching already published pharmacophores. Many of the analogues were shown to have neuroprotective properties in two assays using primary cultures of cortical neurons exposed to glutamate and hydrogen peroxide. However, no apparent SAR for these two assays could be developed. Metabolic stability of the analogues were also investigated and the structure of R¹ had a significant bearing on the ADME properties of the compound resulting in two series of compounds. Compounds in which R¹ was a H or acyl group had good metabolic stability in RLM but poor BBB penetration, whereas compounds where R¹ was a cyclo- or bicyclo-alkyl group had poor metabolic stability but good BBB penetration.     

Amine-free melanin-concentrating hormone receptor 1 antagonists: Novel 1-(1H-benzimidazol-6-yl)pyridin-2(1H)-one derivatives and design to avoid CYP3A4 time-dependent inhibition

Melanin-concentrating hormone (MCH) is an attractive target for antiobesity agents, and numerous drug discovery programs are dedicated to finding small-molecule MCH receptor 1 (MCHR1) antagonists. We recently reported novel pyridine-2(1H)-ones as aliphatic amine-free MCHR1 antagonists that structurally featured an imidazo[1,2-a]pyridine-based bicyclic motif. To investigate imidazopyridine variants with lower basicity and less potential to inhibit cytochrome P450 3A4 (CYP3A4), we designed pyridine-2(1H)-ones bearing various less basic bicyclic motifs. Among these, a lead compound 6a bearing a 1H-benzimidazole motif showed comparable binding affinity to MCHR1 to the corresponding imidazopyridine derivative 1. Optimization of 6a afforded a series of potent thiophene derivatives (6q–u); however, most of these were found to cause time-dependent inhibition (TDI) of CYP3A4. As bioactivation of thiophenes to form sulfoxide or epoxide species was considered to be a major cause of CYP3A4 TDI, we introduced electron withdrawing groups on the thiophene and found that a CF₃ group on the ring or a Cl adjacent to the sulfur atom helped prevent CYP3A4 TDI. Consequently, 4-[(5-chlorothiophen-2-yl)methoxy]-1-(2-cyclopropyl-1-methyl-1H-benzimidazol-6-yl)pyridin-2(1H)-one (6s) was identified as a potent MCHR1 antagonist without the risk of CYP3A4 TDI, which exhibited a promising safety profile including low CYP3A4 inhibition and exerted significant antiobesity effects in diet-induced obese F344 rats.     

Design,synthesis, radiolabeling and in vivo evaluation of potential positron emission tomography (PET) radioligands for brain imaging of the 5-HT7 receptor

Here we describe the design, synthesis, and pharmacological evaluation of a set of compounds structurally related to the high affinity serotonin 5-HT₇ receptor agonist N-(4-cyanophenylmethyl)-4-(2-diphenyl)-1-piperazinehexanamide (6, LP-211). Specific structural modifications were performed in order to maintain affinity for the target receptor and to improve the selectivity over 5-HT_1A and adrenergic α₁ receptors. The synthesized compounds have chemical features that could enable labeling with a positron emitter radioisotope (carbon-11 or fluorine-18) and lipophilicity within the range considered optimal for brain penetration and low non-specific binding. 4-[2-(4-Methoxyphenyl)phenyl]-N-(pyridin-4-ylmethyl)piperazinehexanamide (23a) and N-pyridin-4-ylmethyl-3-[4-[2-(4-methoxyphenyl)phenyl]piperazin-1-yl]ethoxy]propanamide (26a) were radiolabeled on the methoxy group with carbon-11. Positron emission tomography (PET) analysis revealed that [¹¹C]-23a and [¹¹C]-26a were P-glycoprotein (P-gp) substrates and rapidly metabolized, resulting in poor brain uptake. These features were not predicted by in vitro tests.     

Discovery of novel α7 nicotinic receptor antagonists

Two distinct families of small molecules were discovered as novel α7 nicotinic acetylcholine receptor (nAChR) antagonists by pharmacophore-based virtual screening. These novel antagonists exhibited selectivity for the neuronal α7 subtype over other nAChRs and good brain penetration. Neuroprotection was demonstrated by representative compounds 7i and 8 in a mouse seizure-like behavior model induced by the nerve agent diisopropylfluorophosphate (DFP). These novel nAChR antagonists have potential use as antidote for organophosphorus nerve agent intoxication.     

New quinoline NK3 receptor antagonists with CNS activity

Lead optimisation starting from the previously reported selective quinoline NK₃ receptor antagonists talnetant 2 (SB-223412) and 3 (SB-222200) led to the identification of 3-aminoquinoline NK₃ antagonist 10 (GSK172981) with excellent CNS penetration. Investigation of a structurally related series of sulfonamides with reduced lipophilicity led to the discovery of 20 (GSK256471). Both 10 and 20 are high affinity, potent NK₃ receptor antagonists which despite having different degrees of CNS penetration produced excellent NK₃ receptor occupancy in an ex vivo binding study in gerbil cortex.     

Chemosystematics of tea trees based on tea leaf polyphenols as phenetic markers

This study examined the polyphenols of tea leaves as chemotaxonomic markers to investigate the phenetic relationship between 89 wild (the small-leaved C. sinensis var. sinensis and large-leaved C. sinensis var. assamica), hybrid, and cultivated tea trees from China and Japan. (?)-Epigallocatechin 3-O-gallate, EGCG (1); (?)-epigallocatechin, EGC (2); (?)-epicatechin 3-O-gallate, ECG (3); (?)-epicatechin, EC (4); (+)-catechin, CA (5); strictinin, STR (6); and gallic acid, GA (7) were used as polyphenolic markers. Of the 13 polyphenol patterns observed, Principal Component Analysis (PCA) indicated that the structure-types of the flavonoid B-rings, such as the pyrogallol-(EGCG (1) and EGC (2)) and catechol-(ECG (3) and EC (4)) types, greatly influenced the classification. Ward’s minimum-variance cluster analysis was used to produce a dendrogram that consisted of three sub-clusters. One sub-cluster (A) was composed of old tea trees ‘Gushu’ cha (C. sinensis var. assamica) and cv ‘Taidi’ cha, suggesting that relatively primitive tea trees contain greater amounts of compounds 3 and 4 and lower amounts of compounds 1 and 2. The other two sub-clusters B and C, made up of Chinese hybrids (sub-cluster B) and Japanese and Taiwanese tea trees (sub-cluster C), had lower contents of 3 and 4 than sub-cluster A. Therefore, PCA and cluster analysis indicated that the greater the amounts of 1 and 2 (and the lower of 3 and 4), the more recent the origin of the tea line. Based on morphological characteristics, geographical information, and the historical information on tea trees, these results show good agreement with the current theory of tea tree origins, and this suggests that the Xishuangbanna district and Puer City are among the original sites of the tea tree species.     

Selective oxidation-reduction and esterification of asiatic acid by Pestalotiopsis microspora and anti-HCV activity

Microbial transformation of asiatic acid (AA) by an endophytic fungus, Pestalotiopsis microspora, yielded six metabolites: 2-oxo-3β,15α,23-trihydroxyurs-12-ene-28-oic acid (1); 2-oxo-3β,15α,22α,23-tetrahydroxyurs-12-ene-28-oic acid (2); 2-oxo-3β,15α,23,30-tetrahydroxyurs-12-ene-28-oic acid (3); 2α,3β,15α,23,30-pentahydroxyurs-12-ene-28-oic acid methyl ester (4); 2α,3α,15α,23-tetrahydroxyurs-12-ene-28-oic acid (5); 2α,3α,15α,23,30-pentahydroxyurs-12-ene-28-oic acid (6). The structure elucidation of these products was confirmed based on the spectroscopic data. Compounds 2–6 were new. A possible biotransformation pathway is proposed. The anti-HCV activity of compounds 1–6 was also evaluated.     

Synthesis,SAR study,and biological evaluation of novel 2,3-dihydro-1H-imidazo[1,2-a]benzimidazole derivatives as phosphodiesterase 10A inhibitors

Phosphodiesterase 10A (PDE10A) inhibitors were designed and synthesized based on the dihydro-imidazobenzimidazole scaffold. Compound 5a showed moderate inhibitory activity and good permeability, but unfavorable high P-glycoprotein (P-gp) liability for brain penetration. We performed an optimization study to improve both the P-gp efflux ratio and PDE10A inhibitory activity. As a result, 6d was identified with improved P-gp liability and high PDE10A inhibitory activity. Compound 6d also showed satisfactory brain penetration, suppressed phencyclidine-induced hyperlocomotion and improved MK-801-induced working memory deficit.     

Synthesis and biological evaluation of radio-iodinated benzimidazoles as SPECT imaging agents for NR2B subtype of NMDA receptor

In this study, the benzimidazole derivatives were synthesized and evaluated as imaging agents for the NR2B subtype of NMDA receptor. Among these ligands, 2-{[4-(4-iodobenzyl)piperidin-1-yl]methyl}benzimidazol-5-ol (8) and N-{2-[4-(4-iodobenzyl)-piperidin-1-ylmethyl]benzoimidazol-5-yl}-methanesulfonamide (9) exhibited high affinity for the NR2B subunit (K_i values; 7.28 nM for 8 and 5.75 nM for 9). In vitro autoradiography experiments demonstrated high accumulation in the forebrain regions but low in the cerebellum for both [¹²⁵I]8 and [¹²⁵I]9. These regional distributions of the radioligands correlated with the expression of the NR2B subunit. The in vitro binding of these ligands was inhibited by NR2B antagonist but not by other site ligands, which suggested the high selectivity of [¹²⁵I]8 and [¹²⁵I]9 for the NR2B subunit. In mice, the regional brain uptakes of [¹²⁵I]8 and [¹²⁵I]9 at 5–180 min after administration were 0.42–0.56% and 0.44–0.67% dose/g, respectively. The brain-to-blood ratio of [¹²⁵I]8 at 180 min was reduced by 34% in the presence of non-radioactive ligands and by 59% in the presence of the NR2B ligand Ro-25,6981. These results indicated that [¹²⁵I]8 could be partially bound to the NR2B subunit in vivo. Although the brain uptake of these benzimidazole derivatives was too low to allow for in vivo SPECT imaging, these compounds might be useful scaffolds for the development of imaging probes specific for the NMDA receptors.