Synthesis and in vitro binding of N-phenyl piperazine analogs as potential dopamine D3 receptor ligands

A series of N-(2-methoxyphenyl)piperazine and N-(2,3-dichlorophenyl)piperazine analogs were prepared and their affinities for dopamine D(2), D(3), and D(4) receptors were measured in vitro. Binding studies were also conducted to determine if the compounds bound to sigma (sigma(1) and sigma(2)) and serotonin (5-HT(1A), 5-HT(2A), 5-HT(2B), 5-HT(2C), 5-HT(3), 5-HT(4), 5-HT(5), 5-HT(6), and 5-HT(7)) receptors. The results of the current study revealed a number of compounds (12b, 12c, 12e, and 12g) having a high affinity for D(3) (K(i) at D(3) receptors ranging from 0.3 to 0.9 nM) versus D(2) (K(i) at D(2) receptors ranging from 40 to 53 nM) receptors and a log P value indicating that they should readily cross the blood brain barrier (log P = 2.6-3.5). All of the compounds evaluated in this study had a high affinity for serotonin 5-HT(1A) receptors. These compounds may be useful as probes for studying the behavioral pharmacology of the dopamine D(3) receptor, as well as lead compounds for the development of radiotracers for studying D(3) receptor regulation in vivo with the functional imaging technique, positron emission tomography.     

Estrogen receptor beta selective ligands: discovery and SAR of novel heterocyclic ligands

A series of ligands with varying heterocyclic cores and substituents that display a range of selectivity’s (up to >100x) for ER-β over ER- are reported.     

Design,synthesis and biological evaluation of bitopic arylpiperazine-hexahydro-pyrazinoquinolines as preferential dopamine D3 receptor ligands

Three series of bitobic arylpiperazine-phenyl-hexahydropyrazinoquino- lines analogues were designed, synthesizedand evaluated as a novel class of selective ligands for the dopamine D3 receptor. Compounds 15a (K_i of 11.7 ± 1.8 and 373 nM at D3 and D2, respectively), 15c (K_i of 5.49 and 264 nM at D3 and D2, respectively), 15e (K_i of 14.9 and 325 nM at D3 and D2, respectively), 15i (K_i of 13.8 and 401 nM at D3 and D2, respectively) and 15l (K_i of 13.6 and 870 nM at D3 and D2, respectively) were found to demonstrate good binding affinity and selectivity, and especially compound 15c showeda similar binding affinity and selectivity compared with the contrast drug BP897.     

Preparation and biological evaluation of 18F-labeled benzamide analogs as potential dopamine D2 receptor ligands

Three ¹⁸F-labeled benzamide derivatives were prepared and evaluated as potential ligands to study the dopamine D₂ receptor phenomenon. The compounds are analogs of iodobenzamide, eticlopride and raclopride and are labeled with an N-2-[¹⁸F]fluoroethyl functionality on the pyrrolidine ring. The compounds were tested in vitro for binding affinity and found to exhibit somewhat lower affinity than the non-fluorinated analog. In vivo distribution studies revealed that all compounds were more highly bound to plasma proteins than was raclopride. In addition, compartmentation of radioactivity demonstrated nonspecific binding to be the predominate retention in the brain as reflected by the low caudate to cerebellum ratios for these compounds. These three ¹⁸F-labeled benzamide derivatives are inferior to raclopride and iodobenzamide for studies of the D₂ receptor system using positron emission tomography.     

Tetrahydroisoquinolines functionalized with carbamates as selective ligands of D2 dopamine receptor

A series of tetrahydroisoquinolines functionalized with carbamates is reported here as highly selective ligands on the dopamine D2 receptor. These compounds were selected by means of a molecular modeling study. The studies were carried out in three stages: first an exploratory study was carried out using combined docking techniques and molecular dynamics simulations. According to these results, the bioassays were performed; these experimental studies corroborated the results obtained by molecular modeling. In the last stage of our study, a QTAIM analysis was performed in order to determine the main molecular interactions that stabilize the different ligand-receptor complexes. Our results show that the adequate use of combined simple techniques is a very useful tool to predict the potential affinity of new ligands at dopamine D1 and D2 receptors. In turn the QTAIM studies show that they are very useful to evaluate in detail the molecular interactions that stabilize the different ligand-receptor complexes; such information is crucial for the design of new ligands.     

N-8-Substituted benztropinamine analogs as selective dopamine transporter ligands

A series of N-8-substituted benztropinamines was synthesized and evaluated for binding at the dopamine (DAT), serotonin (SERT), norepinephrine (NET) transporters, and muscarinic M1 receptors. In general, the isosteric replacement of the C-3 benzhydrol ether of benztropine by a benzhydryl amino group was well tolerated at the DAT. However, for certain N-8 substituted derivatives, selectivity over muscarinic M1 receptor affinity was reduced.     

Design of novel hexahydropyrazinoquinolines as potent and selective dopamine D3 receptor ligands with improved solubility

We have recently reported hexahydropyrazinoquinolines as a new class of dopamine 3 (D(3)) receptor ligands with high-affinity to the D(3) receptor and excellent selectivity over the closely related D(1)-like and D(2)-like receptors. However, our previously reported most potent and selective D(3) ligands have poor aqueous solubility, which greatly hinders our in vivo studies aimed at evaluation of their therapeutic potential in animal models. In this study, we wish to report the design, synthesis, and evaluation of a series of new hexahydropyrazinoquinolines as D(3) ligands with improved solubility. Among them, compound 4g has a K(i) value of 9.7 nM for the D(3) receptor and displays a selectivity of >5000 and 466 times over the D(1)-like and D(2)-like receptors, respectively. Importantly, the hydrochloride salt form of compound 4g has a good aqueous solubility (>50 mg/mL) and represents a promising D(3) ligand for further in vivo evaluations of its therapeutic potential for the treatment of drug abuse, restless legs syndrome, schizophrenia, Parkinson's disease, and depression.     

Synthesis and radioiodination of selective ligands for the dopamine D3 receptor subtype

Starting from FAUC 365, a series of iodine substituted heteroaryl carboxamides has been synthesized revealing high affinity and selectivity for the dopamine D3 receptor. Binding data showed a 15-560-fold selectivity for the dopamine D3 over D2. A 2,3-dichloro substitution pattern on the phenylpiperazine moiety led to the highest subtype selectivity, whereas the 2-methoxy substituted compounds showed superior D3 affinity. Suitable precursors were radioiodinated with high radiochemical yields (53-85%) leading to potential imaging agents for the D3 receptor by SPET.     

Synthesis and binding affinity of new 1,4-disubstituted triazoles as potential dopamine D3 receptor ligands

A series of new 1,4-disubstituted triazoles was prepared from appropriate arylacetylenes and aminoalkylazides using click chemistry methodology. These compounds were evaluated as potential ligands on several subtypes of dopamine receptors in in vitro competition assays, showing high affinity for dopamine D₃ receptors, lower affinity for D₂ and D₄, and no affinity for the D₁ receptors. Compound 18 displayed the highest affinity at the D₃ receptor with a K_i value of 2.7 nM, selectivity over D₂ (70-fold) and D₄ (200-fold), and behaviour as a competitive antagonist in the low nanomolar range.     

Synthesis and evaluation of 18F-labeled dopamine D3 receptor ligands as potential PET imaging agents

A series of fluoro substituted aryl carboxamides was synthesized revealing high affinity for the dopamine D3 receptor. In contrast to 2-methoxy substitution, a 2,3-dichloro substitution pattern at the phenylpiperazine moiety induces a 10-fold increase of D3 affinity which is expressed by Ki values of 0.53, 1.1, and 9.0 nM for 8b, 8d, and 8f. Applying aromatic 18F-for-Br(Cl) substitution, high radiochemical yields between 76-82% were obtained for [18F]8c-f. The most promising ligand, [18F]8d, was used as imaging agent of the D3 receptor in vitro. However, due to the lack of specific binding, further studies should aim at the development of radioligands with improved D3 receptor selectivity.     

Discovery of new SCH 39166 analogs as potent and selective dopamine D1 receptor antagonists

A series of novel dopamine D₁ antagonists derived from functionalization of the D-ring of SCH 39166 were prepared. A number of these compounds displayed subnanomolar D₁ activity and more than 1000-fold selectivity over D₂. We found C-3 derivatization afforded compounds with superior overall profile in comparison to the C-2 and C-4 derivatization. A number of highly potent D₁ antagonists were discovered which have excellent selectivity over other dopamine receptors and improved PK profile compared to SCH 39166.     

New analogs of SYA013 as sigma-2 ligands with anticancer activity

Our previous study has revealed 4-(4-(4-chlorophenyl)-1,4-diazepan-1-yl)-1-(4-fluorophenyl)butan-1-one·2HCl (SYA013) 1 as a sigma ligand with moderate selectivity for the sigma-2 receptor. Given the overexpression of sigma receptors in solid tumors and reports of sigma ligands with anticancer activities, we selected 1 for evaluation in several solid tumor cell lines. In addition, we have synthesized new analogs of 1 and now report that several of them bind preferentially at the sigma-2 receptor and have shown inhibition of several cancer cell lines including MDA-MB-231, MDA-MB-486, A549, PC-3, MIA PaCa-2 and Panc-1 cells. In particular, compounds 1 and 12 have demonstrated sub-micromolar activity against the Panc-1 cell line. It has also been observed that several of these compounds demonstrate selective toxicity toward cancer cells, when compared to normal cells.     

Conformationally-flexible benzamide analogues as dopamine D3 and sigma 2 receptor ligands

A series of conformationally-flexible analogues was prepared and their affinities for D2-like dopamine (D2, D3 and D4) were determined using in vitro radioligand binding assays. The results of this structure-activity relationship study identified one compound, 15, that bound with high affinity (K(i) value=2nM) and moderate selectivity (30-fold) for D3 compared to D2 receptors. In addition, this series of compounds were also tested for affinity at sigma1 and sigma2 receptors. We evaluated the affinity of these dopaminergic compounds at sigma receptors because (a) several antipsychotic drugs, which are high affinity antagonists at dopamine D2-like receptors, also bind to sigma receptors and (b) sigma receptors are expressed ubiquitously and at high levels (picomoles per mg proteins). It was observed that a number of analogues displayed high affinity and excellent selectivity for sigma2 versus sigma1 receptors. Consequently, these novel compounds may be useful for characterizing the functional role of sigma2 receptors and for imaging the sigma2 receptor status of tumors in vivo with PET.     

Conformationally constrained analogs of BAY 59-3074 as novel cannabinoid receptor ligands

To obtain information on the pharmacophoric requirements of the CB1/CB2 partial agonist BAY 59-3074 we have synthesized a series of new conformationally constrained dibenzofuran (4a-d) and dibenzopyran analogs (5). All constrained analogs exhibited reduced binding affinity at both cannabinoid receptor subtypes, suggesting that planar conformations of these ligands are less favored by both receptors. We also found that 4c, 4d, and 5 exhibited 3- to 12-fold selectivity for hCB2 over rCB1 receptors and may serve as new chemotypes for the development of CB2-selective cannabinergics.     

Click chemistry based synthesis of dopamine D4 selective receptor ligands for the selection of potential PET tracers

Taking advantage of click chemistry, a library of N-arylpiperazinylmethyl triazoles bearing fluoro substituted appendages was synthesized and the target compounds were investigated for dopamine and serotonin receptor binding. With the aim to bias their hydrophilicity and to optimize their D4 receptor affinity and selectivity, a concise series of triazoles containing fluoroalkyl, fluoroalkoxy, fluoroalkoxyphenyl, and deoxyfluoroglucosyl substituents was studied. The D4 receptor affinity and selectivity could be tuned by altering the chemical moiety attached to the triazole unit. Among the test compounds, the fluoroethoxyphenyl derivative 15b showed weak partial agonism at D4 and a K_i value of 14 nM, while its fluoropropoxyphenyl homologue 16a turned out to act as a neutral D4 antagonist (K_i = 5.1 nM). Both, 15b and 16a revealed an excellent balance between D4 receptor affinity and subtype selectivity, providing lead candidates for the development of ¹⁸F-labeled radioligands for D4 receptor imaging studies by positron emission tomography (PET).     

A solid phase parallel synthesis of diverse amides as dopamine D3 receptor ligands

A solid phase parallel synthesis using SynPhase technology was used to couple a series of 21 carboxylic with three different 4-(4-arylpiperazinyl)butanamines. The resulting library was evaluated as dopamine D(3) receptor ligands giving rise to several compounds with affinities in the low nanomolar concentration range (9e and 9n with binding affinities at D(3) receptors of 0.10 and 0.35 nM respectively).     

A solid phase parallel synthesis of diverse amides as dopamine D3 receptor ligands

A solid phase parallel synthesis using SynPhase? technology was used to couple a series of 21 carboxylic with three different 4-(4-arylpiperazinyl)butanamines. The resulting library was evaluated as dopamine D₃ receptor ligands giving rise to several compounds with affinities in the low nanomolar concentration range (9e and 9n with binding affinities at D₃ receptors of 0.10 and 0.35 nM respectively).     

Comparative efficacy of VIP and analogs on activation and internalization of the recombinant VPAC2 receptor expressed in CHO cells

Using a monoclonal antibody interacting with the extracellular amino-terminus of the human VPAC₂ receptor but that did not interfere with ligand binding, we measured by flow cytometry receptor internalization and trafficking induced by full agonists, partial agonists and an antagonist in Chinese hamster ovary cells expressing the recombinant receptor. The agonists, but not the antagonist, induced a rapid, dose-dependent receptor internalization blocked by hypertonic sucrose that was more pronounced for the VIP analog N-hexanoyl-VIP (80%) than for VIP and Ro 25-1553 (50%) and the [A¹¹]-VIP (20%). Re-expression of the receptors at the membrane was achieved within two hours after exposure to VIP and Ro 25-1553 was blocked by 25 μM monensin but not by 10 μg/ml cycloheximide. Re-expression was much slower after exposure to the acylated peptide and was blocked by preincubation with 25 μM monensin and 10 μg/ml cycloheximide.     

Structure–activity relationship analysis of carbobicyclo and oxabicyclo succinimide analogs as potential androgen receptor antagonists

Prostate cancer (PCa) is a frequently diagnosed male cancer and the second leading cause of cancer-related death in many countries. Due to various amino acid mutations that occurred in the ligand binding domain of androgen receptor (AR), the patients were observed insensitive, even resistant to the marketed antiandrogens such as bicalutamide and enzalutamide, which emphasizes the urgent need for novel antiandrogens to solve drug resistance problem. Recently a series of carbobicyclo and oxabicyclo succinimide analogs were reported to effectively antagonize AR. In this study, to explore the structural requirements for these AR antagonists, we performed quantitative structure–activity relationship analysis on carbobicyclo and oxabicyclo succinimide analogs by using two-dimensional multiple linear regressions (MLR) method and three-dimension comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) methods. The obtained models show satisfactory results with proper reliabilities and powerful external predictability. Moreover, the CoMFA and CoMSIA contour maps can intuitively represent key features associated with bioactivities. These models may offer guidance for the rational design and modification of new lead compounds for antiandrogens.     

Synthesis and evaluation of novel azetidine analogs as potent inhibitors of vesicular [3H]dopamine uptake

Lobelane analogs that incorporate a central piperidine or pyrrolidine moiety have previously been reported by our group as potent inhibitors of VMAT2 function. Further central ring size reduction of the piperidine moiety in lobelane to a four-membered heterocyclic ring has been carried out in the current study to afford novel cis-and trans-azetidine analogs. These azetidine analogs (15a–15c and 22a–22c) potently inhibited [³H]dopamine (DA) uptake into isolated synaptic vesicles (K_i ? 66 nM). The cis-4-methoxy analog 22b was the most potent inhibitor (K_i = 24 nM), and was twofold more potent that either lobelane (2a, K_i = 45 nM) or norlobelane (2b, K_i = 43 nM). The trans-methylenedioxy analog, 15c (K_i = 31 nM), was equipotent with the cis-analog, 22b, in this assay. Thus, cis- and trans-azetidine analogs 22b and 15c represent potential leads in the discovery of new clinical candidates for the treatment of methamphetamine abuse.