Radiosynthesis and evaluation of new PET ligands for peripheral cannabinoid receptor type 1 imaging

Cannabinoid receptor type 1 (CB1) is mainly expressed in the brain, as well as being expressed in functional relevant concentrations in various peripheral tissues. 1-(4-Chlorophenyl)-3-(3-(6-(pyrrolidin-1-yl)pyridin-2-yl)phenyl)urea (PSNCBAM-1, 1) was developed as a potent allosteric antagonist for CB1 and its oral administration led to reductions in the appetite and body weight of rats. Several analogs of 1 (compounds 2 and 3) were recently identified through a series of structure-activity relationship studies. Herein, we report the synthesis of radiolabeled analogs of these compounds using [¹¹C]COCl₂ and an evaluation of their potential as PET ligands for CB1 imaging using in vitro and in vivo techniques. [¹¹C]2 and [¹¹C]3 were successfully synthesized in two steps using [¹¹C]COCl₂. The radiochemical yields of [¹¹C]2 and [¹¹C]3 were 17 ± 8% and 20 ± 9% (decay-corrected to the end of bombardment, based on [¹¹C]CO₂). The specific activities of [¹¹C]2 and [¹¹C]3 were 42 ± 36 and 37 ± 13 GBq/μmol, respectively. The results of an in vitro binding assay using brown adipose tissue (BAT) homogenate showed that the binding affinity of 2 for CB1 (K_D = 15.3 µM) was much higher than that of 3 (K_D = 26.0 µM). PET studies with [¹¹C]2 showed a high uptake of radioactivity in BAT, which decreased in animals pretreated with AM281 (a selective antagonist for CB1). In conclusion, [¹¹C]2 may be a useful PET ligand for imaging peripheral CB1 in BAT.     

Oxadiazole-diarylpyrazole 4-carboxamides as cannabinoid CB1 receptor ligands

Cannabinoid CB-1 receptors have been the focus of extensive studies since the first clinical results of rimonabant (SR141716) for the treatment of obesity and obesity-related metabolic disorders were reported in 2001. To further evaluate the properties of CB receptors, we have designed and efficiently prepared a series of oxadiazole-diarylpyrazole 4-carboxamides. Six of the new compounds which displayed high in vitro CB1 binding affinities were assayed for binding to CB2 receptor. Noticeably, 5-(4-bromophenyl)-3-(5-tert-butyl-1,3,4-oxadiazol-2-yl)-1-(2,4-dichlorophenyl)-N-phenyl-1H-pyrazole-4-carboxamide (12q) and 5-(4-bromophenyl)-3-(5-tert-butyl-1,3,4-oxadiazol-2-yl)-1-(2,4-dichlorophenyl)-N-(pyridin-2-yl)-1H-pyrazole-4-carboxamide (12r) demonstrated good binding affinity and decent selectivity for CB1 receptor (IC₅₀ = 1.35 nM, CB2/CB1 = 286 for 12q; IC₅₀ = 1.46 nM, CB2/CB1 = 256 for 12r).     

Evaluation of (Z)-2-((1-benzyl-1H-indol-3-yl)methylene)-quinuclidin-3-one analogues as novel,high affinity ligands for CB1 and CB2 cannabinoid receptors

A small library of N-benzyl indolequinuclidinone (IQD) analogs has been identified as a novel class of cannabinoid ligands. The affinity and selectivity of these IQDs for the two established cannabinoid receptor subtypes, CB1 and CB2, was evaluated. Compounds 8 (R = R² = H, R¹ = F) and 13 (R = COOCH₃, R¹ = R² = H) exhibited high affinity for CB2 receptors with K_i values of 1.33 and 2.50 nM, respectively, and had lower affinities for the CB1 receptor (K_i values of 9.23 and 85.7 nM, respectively). Compound 13 had the highest selectivity of all the compounds examined, and represents a potent cannabinoid ligand with 34-times greater selectivity for CB2R over CB1R. These findings are significant for future drug development, given recent reports demonstrating beneficial use of cannabinoid ligands in a wide variety of human disease states including drug abuse, depression, schizophrenia, inflammation, chronic pain, obesity, osteoporosis and cancer.     

Substituted pyrimidines as cannabinoid CB1 receptor ligands

Cannabinoid CB1 receptors have been the avenue of extensive studies since the first clinical results of rimonabant (SR141716) for the treatment of obesity and obesity-related metabolic disorders were reported in 2001. To further evaluate the properties of CB receptors, we have designed and efficiently prepared a series of substituted pyrimidines based on chemical structure of Merck’s taranabant, a cannabinoid CB1 receptor inverse agonist. Noticeably, N4-((2S,3S)-3-(3-bromophenyl)-4-(4-chlorophenyl)butan-2-yl)-N6-butylpyrimidine-4,6-diamine (13b) demonstrated good binding affinity and decent selectivity for CB1 receptor (IC₅₀ = 16.3 nM, CB2/CB1 = 181.6).     

Diarylimidazolyl oxadiazole and thiadiazole derivatives as cannabinoid CB1 receptor antagonists

Since the CB1 receptor antagonist SR141716 (rimonabant) was reported to modulate food intake, CB1 antagonism has been considered as a new therapeutic target in the treatment of obesity. Several series of derivatives based on diarylimidazolyl oxadiazole and thiadiazole scaffolds were synthesized and tested for CB1 receptor binding affinity. SAR studies directed toward the optimization of imidazole scaffolds resulted in the discovery of 10s which showed highest potency for CB1 receptor binding affinity (IC₅₀ = 1.91 nM) prepared to date.     

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.     

Antitumor agents. 271: Total synthesis and evaluation of brazilein and analogs as anti-inflammatory and cytotoxic agents

The first total synthesis of the naturally occurring tetracyclic homoisoflavonoid brazilein (1) and 14 new analogs (1a–n) is reported. Target compounds and intermediates were assayed for anti-inflammatory effects on superoxide anion generation and elastase release by human neutrophils in response to fMLP/CB, and for cytotoxic activity against nasopharyngeal (KB), vincristine-resistant nasopharyngeal (KBvin), lung (A549) and prostate (DU-145) human cancer cell lines. The most active compound 1b showed potent effects on superoxide anion generation and elastase release with IC₅₀ values of 1.2 and 1.9 μM, respectively, and was 65 times more potent than phenylmethylsulfonyl fluoride (PMSF), the positive control, in the latter assay. Additionally, 1b exhibited broad spectrum in vitro anticancer activity with IC₅₀ values of 6–11 μM against the four tested cancer cell lines.     

Synthesis and CB1 cannabinoid receptor affinity of 4-alkoxycarbonyl-1,5-diaryl-1,2,3-triazoles

A series of 4-alkoxycarbonyl-1,5-diaryl-1,2,3-triazoles were synthesized regioselectively using click chemistry and evaluated at CB1 cannabinoid receptors. The n-propyl ester 11 (K_i = 4.6 nM) and phenyl ester 14 (K_i = 11 nM) exhibited the most potent affinity of the series.     

Identification and hit-to-lead optimization of a novel class of CB1 antagonists

The discovery, synthesis and preliminary structure–activity relationships (SARs) of a novel class of CB1 antagonists is described. Initial optimization of benzimidazole-based screening hit 4 led to the identification of ‘inverted’ indole-based lead compound 18c with improved properties versus compound 4 including reduced A log P, improved microsomal stability and improved aqueous solubility. Compound 18c demonstrates in vivo CB1 antagonist efficacy (CB1 agonist induced hypothermia model) and is orally bioavailable in rat.     

Rat intestinal sucrase inhibition of constituents from the roots of Rosa rugosa Thunb.

A new octanordammarane triterpene, 3β,15α-dihydroxymansumbinol (1) and a novel A-ring contracted oleanane triterpenoid, 2-formyl-(A)1–19α-hydroxy-1-norolean-2,12-dien-28-oic acid (2) were isolated from the roots extract of Rosa rugosa along with fifteen known compounds (3–17). Their structures were elucidated by extensive spectroscopic analysis, including 1D and 2D NMR, and FTICRMS. The MeOH extract, as well as CH₂Cl₂ and EtOAc fractions at a concentration of 0.5 mg/mL showed potent sucrase inhibitory activity, with inhibition percentage values of 84.67 ± 5.37%, 87.50 ± 2.78%, and 81.91 ± 2.90%, respectively. In addition, compounds 7–13 (1.0 mM) showed potent sucrase inhibitory activity (61.88 ± 3.19% to 84.70 ± 3.07% inhibition), which was comparable to that of the positive control, acarbose, with an inhibition percentage value of 50.96 ± 2.97%. Compounds 1, 2, 4, and 14–17 showed moderate and/or weak inhibitory activities at the same concentration. The α-glucosidase inhibitory activities of the extracts and purified compounds may provide a novel opportunity to develop a new class of antidiabetic agents.     

Pentacycle derivatives as cannabinoid CB1 receptor ligands

Cannabinoid CB-1 receptors have been the focus of extensive studies since the first clinical results of rimonabant (SR141716) for the treatment of obesity and obesity-related metabolic disorders were reported in 2001. To further evaluate the properties of CB receptors, we have designed and efficiently prepared a series of pentacycle derivatives. Five of the new compounds which displayed high in vitro rCB1 binding affinities were assayed for binding to hCB2 receptor. Noticeably, 2-(5-(4-bromophenyl)-1-(2,4-dichlorophenyl)-4-(5-methyl-1,3,4-thiadiazol-2-yl)-1H-pyrazol-3-yl)-5-(1-(trifluoromethyl)cyclopropyl)-1,3,4-oxadiazole (16l) demonstrated good binding affinity and decent selectivity for rCB1 receptor (IC₅₀ = 1.72 nM, hCB2/rCB1 = 142).     

Schiff’s base derivatives bearing nitroimidazole and quinoline nuclei: New class of anticancer agents and potential EGFR tyrosine kinase inhibitors

New Schiff’s base derivatives 5a–j have been synthesized by reaction between 2-phenoxyquinoline-3-carbaldehydes 3a–j and 2-(2-methyl-5-nitro-1H-imidazol-1-yl)acetohydrazide 4 in presence of nickel(II) nitrate as a catalyst in ethanol under reflux in good yield (78–92%). All compounds were tested for anticancer and inhibition of EGFR. Of the compounds studied, majority of the compounds showed effective antiproliferation and inhibition of EGFR and HER-2 activities. Compound 5h showed most effective inhibition (IC₅₀ = 0.12 ± 0.05 μM) by binding in to the active pocket of EGFR receptor with minimum binding energy (ΔG_b = −58.3691 kcal/mol). The binding was stabilized by two hydrogen bonds, two π–cation and one π–sigma interactions. Compound 5d showed most effective inhibition (IC₅₀ = 0.37 ± 0.04 μM).     

Identification of new potent inhibitor of aldose reductase from Ocimum basilicum

Recent efforts to develop cure for chronic diabetic complications have led to the discovery of potent inhibitors against aldose reductase (AKR1B1, EC 1.1.1.21) whose role in diabetes is well-evident. In the present work, two new natural products were isolated from the ariel part of Ocimum basilicum; 7-(3-hydroxypropyl)-3-methyl-8-β-O-d-glucoside-2H-chromen-2-one (1) and E-4-(6′-hydroxyhex-3′-en-1-yl)phenyl propionate (2) and confirmed their structures with different spectroscopic techniques including NMR spectroscopy etc. The isolated compounds (1, 2) were evaluated for in vitro inhibitory activity against aldose reductase (AKR1B1) and aldehyde reductase (AKR1A1). The natural product (1) showed better inhibitory activity for AKR1B1 with IC₅₀ value of 2.095 ± 0.77 µM compare to standard sorbinil (IC₅₀ = 3.14 ± 0.02 µM). Moreover, the compound (1) also showed multifolds higher activity (IC₅₀ = 0.783 ± 0.07 µM) against AKR1A1 as compared to standard valproic acid (IC₅₀ = 57.4 ± 0.89 µM). However, the natural product (2) showed slightly lower activity for AKR1B1 (IC₅₀ = 4.324 ± 1.25 µM). Moreover, the molecular docking studies of the potent inhibitors were also performed to identify the putative binding modes within the active site of aldose/aldehyde reductases.     

Schiff bases of 3-formylchromone as thymidine phosphorylase inhibitors

3-Formylchromone (1), 3-methyl-7-hydroxychromone (2) and Schiff bases of 3-formylchromone 3–19 have been synthesized and their anti-thymidine phosphorylase inhibitory activity was evaluated. Compounds 1–19 showed a varying degree of thymidine phosphorylase inhibition with IC₅₀ values 19.77 ± 3.25 to 480.21 ± 2.34 μM. Their activity was compared with the standard 7-deazaxanthine (IC₅₀ = 39.28 ± 0.76 μM). Compound 12 showed an excellent thymidine phosphorylase inhibitory activity with an IC₅₀ value of 19.77 ± 3.25 μM, better than the standard. Compound 4 also showed an excellent inhibitory activity (IC₅₀ = 40.29 ± 4.56 μM). The parent 3-formylchromone (1) and 3-methyl-7-hydroxychromone (2) were found to be inactive. The structures of the compounds were elucidated by using spectroscopic techniques, including ¹H NMR, EI MS, IR, UV and elemental analysis.     

New triterpene saponins from the seed cake of Camellia Oleifera and their cytotoxic activity

Two new oleanane-type triterpene saponins, identified as 16α-hydroxy-22-O-angeloyl-23-formyl-28,31-dihydroxymethylene-olean-12-ene-3β-O-{β-d-galactopyranosyl-(1 → 2)[β-d-xylopyranosyl-(1 → 2)-α-l-arabinopyranosyl(1 → 3)]-β-d-glucopyranosiduronic acid} (oleiferasaponin B₁, 1) and 22-O-hydrocinnamoyl-23-formyl-28-dihydroxymethylene-olean-12-ene-3β-O-{β-d-glucopyranosyl-(1 → 2)[β-d-xylopyranosyl-(1 → 2)-α-l-arabinopyranosyl(1 → 3)]-β-d-glucopyranosiduronic acid} (oleiferasaponin B₂, 2), were isolated from the seed cake of Camellia oleifera Abel. Their structures were established by extensive 1D- and 2D-NMR experiments along with TOF-MS analysis and acid hydrolysis. The cytotoxicity of the isolated compounds was evaluated in four human carcinoma cell lines: A 549, SK-OV-3, SK-MEL-2 and HCT15. Both compounds 1 and 2 exhibited significantly cytotoxic activity with IC₅₀ values of 18.5 μM (A549), 11.3 μM (SK-OV-3), 13.9 μM (SK-MEL-2) and 1.6 μM (HCT15) for 1 and IC₅₀ values of 8.4 μM (A549), 6.3 μM (SK-OV-3), 9.2 μM (SK-MEL-2) and 0.8 μM (HCT15) for 2. In addition, compound 2 showed more effective cytotoxic activity than compound 1.     

New cytotoxic dihydrochalcone and steroidal saponins from the aerial parts of Sansevieria cylindrica Bojer ex Hook

A new dihydrochalcone, 2‘,4‘-dihydroxy-3‘-methoxy-3,4-methylenedioxy-8-hydroxymethylene dihydrochalcone 1 and two new steroidal saponins, (25S)-ruscogenin-1-O-α-l-rhamnopyranosyl-(1 → 2)-β-d-glucopyranoside 2, (25S)-ruscogenin-3-O-α-l-rhamnopyranosyl-(1 → 4)-β-d-glucopyranoside 3, together with three known steroidal saponins (25S)-ruscogenin-3-O-β-d-glucopyranoside 4, (25S)-ruscogenin-1-O-α-l-rhamnopyranosyl-(1 → 2)-[β-d-xylopyranosyl-(1 → 3)]-α-l-arabinopyranoside 5 and (25R)-26-O-β-d-glucopyranosyl-furost-5-ene-1β,3β,22α,26-tetrol-1-O-α-L-rhamnopyranosyl-(1 → 2)-[β-d-xylopyranosyl-(1 → 3)]-α-l-arabinopyranoside 6 were isolated from the aerial parts of Sansevieria cylindrica. The structures of the new compounds were established by UV, IR, EI-MS, HR-ESI–MS as well as 1D (¹H,¹³C and DEPT-135) and 2D (HSQC, HMBC and TOCSY) NMR spectral analysis. The isolated compounds 1-6 were assayed for in vitro cytotoxicities against the three human tumor cell lines HT116, MCF7 and HepG2. Compound 1 showed a moderate cytotoxicity against MCF7. Compounds 2, 3 and 6 exhibited moderate cytotoxicities against the three used cell lines and compound 5 showed marked cytotoxicities against all used cell lines.     

Ecliptamines A–D,four new guanidine alkaloids from Eclipta prostrata L.

Four structurally unique guanidine alkaloids ecliptamines A–D (1–4) and one known analog (5) were isolated from the aerial parts of Eclipta prostrata (Asteraceae). Their structures were elucidated on the basis of spectroscopic analyses and chemical methods. The inhibitory activities of 1, 2 and 5 were assayed with respect to cyclooxygenase-1 (COX-1) and -2 (COX-2). Compound 5 showed moderate inhibitory activities against COX-1 and -2 with IC₅₀ values of 3.0 × 10⁻³ M and 8.3 × 10⁻⁴ M, respectively, whereas aspirin as a positive control displayed the IC₅₀ values of 4.2 × 10⁻⁴ M (against COX-1) and 7.1 × 10⁻⁴ M (against COX-2).     

Isolation,identification, and bioactivity of microbial metabolites of cyclopamine and its congeners

The biotransformation of cyclopamine (1) and its congeners (2, 3 and 4) by Cunninghamella echinulata (ACCC 30369) was investigated. The chemical structures of two new congeners (2 and 4) and nine new metabolites were elucidated by 1D NMR (¹H, ¹³C and DEPT), 2D NMR (COSY, HMBC, HSQC and NOESY) and HRESIMS analyses and further confirmed by X-ray diffraction studies. Among these compounds, 2 and 4 showed moderate cytotoxicity in HepG2 cells (2, IC₅₀ = 8.03 ± 1.92 μM) and A549 cells (4, IC₅₀ = 10.19 ± 2.18 μM). Conversely, the cytotoxicity of the nine metabolites was sharply reduced. Similar to 1, compound 4 induced a cyclopia phenotype in zebrafish embryos at 20 μM. Moreover, compound 4 was more stable than 1 in an acidic environment.     

Design,synthesis, and X-ray structural studies of BACE-1 inhibitors containing substituted 2-oxopiperazines as P1′-P2′ ligands

We report the design and synthesis of a series of BACE1 inhibitors incorporating mono- and bicyclic 6-substituted 2-oxopiperazines as novel P1′ and P2′ ligands and isophthalamide derivative as P2-P3 ligands. Among mono-substituted 2-oxopiperazines, inhibitor 5a with N-benzyl-2-oxopiperazine and isophthalamide showed potent BACE1 inhibitory activity (K_i = 2 nM). Inhibitor 5g, with N-benzyl-2-oxopiperazine and substituted indole-derived P2-ligand showed a reduction in potency. The X-ray crystal structure of 5g-bound BACE1 was determined and used to design a set of disubstituted 2-oxopiperazines and bicyclic derivatives that were subsequently investigated. Inhibitor 6j with an oxazolidinone derivative showed a BACE1 inhibitory activity of 23 nM and cellular EC₅₀ of 80 nM.     

Molecular design,synthesis and biological evaluation of cyclic imides bearing benzenesulfonamide fragment as potential COX-2 inhibitors. Part 2

A group of cyclic imides (1–10) was designed for evaluation as a selective COX-2 inhibitors and investigated in vivo for their anti-inflammatory activity. Compounds 6a, 6b, 8a, 8b, 9a, 9b, 10a and 10b were proved to be potent COX-2 inhibitors with IC₅₀ range of 0.1–4.0 μM. In vitro COX-1/COX-2 inhibition structure–activity studies identified compound 8a as a highly potent (IC₅₀ = 0.1 μM), and an extremely selective [COX-2 (SI) > 1000] comparable to celecoxib [COX-2 (SI) > 384], COX-2 inhibitor that showed superior anti-inflammatory activity (ED₅₀ = 72.4 mg/kg) relative to diclofenac (ED₅₀ = 114 mg/kg). Molecular modeling was carried out through docking the designed compounds into the COX-2 binding site to predict if these compounds have analogous binding mode to the COX-2 inhibitors. The study showed that the homosulfonamide fragment of 8a inserted deep inside the 2°-pocket of the COX-2 active site, where the SO₂NH₂ group underwent H-bonding interaction with Gln¹⁹²(2.95 Å), Phe⁵¹⁸(2.82 Å) and Arg⁵¹³(2.63 and 2.73 Å). Docking study of the synthesized compound 8a into the active site of COX-2 revealed a similar binding mode to SC-558, a selective COX-2 inhibitor.