2-Phenyl-4(5)-[[4-(pyrimidin-2-yl)piperazin-1-yl]methyl]imidazole. A highly selective antagonist at cloned human D4 receptors

Design for carbon–carbon bond forming reactions under ambient conditions

The carbon–carbon (C–C) bond forms the ‘backbone’ of nearly every organic molecule, and lies at the heart of the chemical sciences! Let us explore designing of carbon–carbon frameworks at ambient conditions.

Facile Synthesis of 2,2-Bis(1 H-Indol-3-yl)Acenaphthen-1(2H)-One Derivatives Catalysed by Ceric Ammonium Nitrate

Ceric ammonium nitrate efficiently catalyses the reaction of acenaphthenequinone with indoles afforded symmetrical 2,2-bis(1H-indol-3-yl)acenaphthen-1(2H)-one in excellent yields within 2h under ethanol refluxing, as well as 2-hydroxy-2-indolylacenaphthen-1(2H)-one with indoles afforded the corresponding unsymmetrical 2,2-bis(1H-indol-3-yl)acenaphthen-1(2H)-one. This provides an efficient route to the synthesis of symmetrical and unsymmetrical 2,2-bis(1H-indol-3-yl)acenaphthen-1(2H)-one derivatives.

Synthesis and evaluation of fluorine-substituted 1H-pyrrolo[2,3-b]pyridine derivatives for dopamine D4 receptor imaging

Seven fluorine-substituted 1H-pyrrolo[2,3-b]pyridine derivatives were synthesized based on a lead ligand, 3-[[4-(4-iodophenyl)piperazin-1-yl]-methyl]-1H-pyrrolo[2,3-b]pyridine (L-750,667) and evaluated as potential dopamine D(4) receptor imaging agents by positron emission tomography (PET). Binding affinities of these ligands for the dopamine D(2), D(3), and D(4) receptor subtypes were measured in vitro. Most ligands showed high and selective binding for the D(4) receptor. Ligand 7 had high affinity for the D(4) receptor, whereas ligands 1, 2, and 6 showed high selectivity for the D(4) receptor. LogP values were calculated for the ligands in this series and ligand 6 had the lowest lipophilicity. (18)F-labeled ligand 7 demonstrated a uniform regional brain distribution and a rapid washout in mice, probably due to nonspecific binding. Based on their in vitro binding properties and calculated logP values, ligand 6 appears to have the most promise for dopamine D(4) receptor imaging.

Neuropharmacological profile of an atypical antipsychotic, NRA0562

Schizophrenia is a serious and disabling psychiatric disorder affecting approximately 1% of the world's population. A new generation of atypical antipsychotics has been introduced over the past decade. These atypical antipsychotics have comparable or greater efficacy than traditional antipsychotics in the treatment of the psychotic symptoms of schizophrenia and a much improved neurologic side effect profile. This paper reviews the pharmacological efficacy and safety of a potential atypical antipsychotic, NRA0562. NRA0562 has a high affinity for dopamine D1, D2L, D4.2, 5-HT2A receptors as well as alpha1-adrenoceptors, and has a moderate affinity for H1 receptors. NRA0562 strongly binds to 5-HT2A receptors and alpha1-adrenoceptors in the frontal cortex, its binding to striatal D2 receptors is weaker, similar to that of clozapine. NRA562 displayed potent antipsychotic activities in animal models of schizophrenia, such as methamphetamine (MAP)-induced hyperactivity, apomorphine-induced disruption of pre-pulse inhibition and conditioned avoidance test. NRA0562 is more potent in reversing the inhibitory effects of MAP at A10 than at A9 dopamine neurons. It increased Fos-like immunoreactivity in the nucleus accumbens more effectively than in the dorsolateral striatum, indicating that NRA0562 has the profile of an atypical antipsychotic. In vivo assays for extrapyramidal side effect liability showed that NRA0562 has a low rate of neurological side effects. Thus, NRA0562 may have unique antipsychotic activity with a lower propensity for extrapyramidal side effects.

A 3D QSAR study on a set of dopamine D4 receptor antagonists

The molecular alignments obtained from a previously reported pharmacophore model have been employed in a three-dimensional quantitative structure-activity relationship (3D QSAR) study, to obtain a more detailed insight into the structure-activity relationships for D(2) and D(4) receptor antagonists. The frequently applied CoMFA method and the related CoMSIA method were used. Statistically significant models have been derived with these two methods, based on a set of 32 structurally diverse D(2) and D(4) receptor antagonists. The CoMSIA and the CoMFA methods produced equally good models expressed in terms of q(2) values. The predictive power of the derived models were demonstrated to be high. Graphical interpretation of the results, provided by the CoMSIA method, brings to light important structural features of the compounds related to either low- or high-affinity D(2) or D(4) antagonism. The results of the 3D QSAR studies indicate that bulky N-substituents decrease D(2) binding, whereas D(4) binding is enhanced. Electrostatically favorable and unfavorable regions exclusive to D(2) receptor binding were identified. Likewise, certain hydrogen-bond acceptors can be used to lower D(2) affinity. These observations may be exploited for the design of novel dopamine D(4) selective antagonists.

Dopaminergic profile of new heterocyclic N-phenylpiperazine derivatives

Dopamine constitutes about 80% of the content of central catecholamines and has a crucial role in the etiology of several neuropsychiatric disorders, including Parkinson's disease, depression and schizophrenia. Several dopaminergic drugs are used to treat these pathologies, but many problems are attributed to these therapies. Within this context, the search for new more efficient dopaminergic agents with less adverse effects represents a vast research field. The aim of the present study was to report the structural design of two N-phenylpiperazine derivatives, compound 4: 1-[1-(4-chlorophenyl)-1H-4-pyrazolylmethyl]-4-phenylhexahydropyrazine and compound 5: 1-[1-(4-chlorophenyl)-1H-1,2,3-triazol-4-ylmethyl]-4-phenylhexahydropyrazine, planned to be dopamine ligands, and their dopaminergic action profile. The two compounds were assayed (dose range of 15-40 mg/kg) in three experimental models: 1) blockade of amphetamine (30 mg/kg, ip)-induced stereotypy in rats; 2) the catalepsy test in mice, and 3) apomorphine (1 mg/kg, ip)-induced hypothermia in mice. Both derivatives induced cataleptic behavior (40 mg/kg, ip) and a hypothermic response (30 mg/kg, ip) which was not prevented by haloperidol (0.5 mg/kg, ip). Compound 5 (30 mg/kg, ip) also presented a synergistic hypothermic effect with apomorphine (1 mg/kg, ip). Only compound 4 (30 mg/kg, ip) significantly blocked the amphetamine-induced stereotypy in rats. The N-phenylpiperazine derivatives 4 and 5 seem to have a peculiar profile of action on dopaminergic functions. On the basis of the results of catalepsy and amphetamine-induced stereotypy, the compounds demonstrated an inhibitory effect on dopaminergic behaviors. However, their hypothermic effect is compatible with the stimulation of dopaminergic function which seems not to be mediated by D2/D3 receptors.

2,4-Disubstituted pyrroles: synthesis, traceless linking and pharmacological investigations leading to the dopamine D4 receptor partial agonist FAUC 356

Solution-phase synthesis and a solid-phase supported approach to piperazinylmethyl substituted pyrroles are described. Receptor binding studies and the measurement of D4 ligand efficacy led to the ethynylpyrrole 1d (FAUC 356) exerting selective D4 binding and substantial ligand efficacy (66%, EC(50)=1.9nM). This activity profile might be of interest for the treatment of ADHD.

InBr3-catalyzed Friedel-Crafts addition of indoles to chiral aromatic epoxides: a facile route to enantiopure indolyl derivatives

Aromatic optically active epoxides can be opened in a regioselective and clean way with indoles in the presence of catalytic amount of InBr3 (1 mol %). The reaction takes place with a SN2 pathway affording the 2-aryl-2-(3'-indolyl)ethan-1-ols with excellent enantioselectivity (ee up to 99%).

Design and synthesis of a piperazinylalkylisoxazole library for subtype selective dopamine receptor ligands

A piperazinylbutylisoxazole libary was designed, synthesized and screened for the binding affinities to dopamine D2, D3, and D4 receptors. Several ligands were identified to possess high binding affinity and selectivity for the D3 and D4 receptors over the D2 receptor. Compounds 6s and 6t showed K(i) values of 2.6 nM and 3.9 nM for the D3 receptor with 46- and 50-fold selectivity over the D2 receptor, respectively.

First direct lithiation of 2-pyridylpiperazine on solid phase

[reaction: see text] The first direct lithiation of a pyridine derivative on solid phase has been realized. Metalation of polymer-bound 2-pyridylpiperazine with the BuLi-LiDMAE reagent followed by electrophilic quenching and subsequent cleavage provided a range of new useful C-6 substituted 2-piperazinylpyridines.

6-(4-Benzylpiperazin-1-yl)benzodioxanes as selective ligands at cloned primate dopamine D(4) receptors

A series of novel 6-(4-benzylpiperazin-1-yl)benzodioxanes were prepared and screened at selected dopamine receptor subtypes. 6-(4-[4-Chlorobenzyl]piperazin-1-yl)benzodioxane (2d) had high affinity and selectivity for the D(4) dopamine receptor subtype and was identified as a D(4) antagonist via its attenuation of dopamine-induced GTPgamma(35)S binding at the D(4) receptor.

Benzamide bioisosteres incorporating dihydroheteroazole substructures: EPC synthesis and SAR leading to a selective dopamine D4 receptor partial agonist (FAUC 179)

Conformationally restricted benzamide bioisosteres were investigated when the chiral phenyldihydroimidazole derivative 4e (FAUC 179) showed strong and highly selective dopamine D4 receptor binding (K(i)high=0.95nM). Mitogenesis experiments indicated partial agonist properties (42%). EPC syntheses of the target compounds of type 4 were performed starting from alpha-amino acids.

Comparative molecular field analysis of dopamine D4 receptor antagonists including 3-[4-(4-chlorophenyl)piperazin-1-ylmethyl]pyrazolo[1,5-a]pyridine (FAUC 113), 3-[4-(4-chlorophenyl)piperazin-1-ylmethyl]-1H-pyrrolo-[2,3-b]pyridine (L-745,870), and clozapine

A CoMFA study was undertaken to elucidate the correlation of biological activity and structural parameters of 25 dopamine D4 antagonists. A special point of interest is that we have included the atypical D4 antagonist clozapine as a structural template for all other compounds. After comparing potential protonation sites at semiempirical (AM1) and ab initio (6-31G(d)) levels of theory, possible conformations of the lead compound 3-[4-(4-chlorophenyl)piperazin-1-ylmethyl]pyrazolo[1,5-a]pyridine (FAUC 113) were investigated by systematic semiempirical conformational analysis. The final conformation of FAUC 113, which was used as a template for the other compounds in the dataset, was chosen by clustering and rigid body alignment of all conformations to clozapine. The CoMFA applied on the final alignment resulted in a q2cv of 0.739. To elucidate the influence of the absolute orientation of the molecules within the grid space, the entire dataset was systematically rotated (1296 steps) within the lattice. The Gaussian-shaped distribution of the q2cv values spanned the range of 0.699-0.794 and therefore supports the significance of the analysis.

trans-1-[(2-Phenylcyclopropyl)methyl]-4-arylpiperazines: mixed dopamine D(2)/D(4) receptor antagonists as potential antipsychotic agents

The dopaminergic receptor profile of a series of trans-1-[(2-phenylcyclopropyl)methyl]-4-arylpiperazines was examined. Aromatic substitution patterns were varied with the goal of identifying a compound having affinities for the D(2) and D(4) receptors in a ratio similar to that observed for the atypical neuroleptic clozapine. The compounds (1S, 2S)-trans-1-[(2-phenylcyclopropyl)methyl]-4-(2, 4-dichlorophenyl)piperazine (5m) and (1S, 2S)-trans-1-[(2-phenylcyclopropyl)methyl]-4-(2, 4-dimethylphenyl)piperazine (5t) were selected for functional antagonists at D(2) and D(4) receptors and had a D(2)/D(4) ratio approximating that of clozapine; they proved inactive in behavioral tests of antipsychotic activity.

Design, synthesis, and discovery of 3-piperazinyl-3,4-dihydro-2(1H)-quinolinone derivatives: a novel series of mixed dopamine D2/D4 receptor antagonists

3-Piperazinyl-3,4-dihydro-2(1H)-quinolinone derivatives (delta-lactams) were designed, synthesized, and identified as a new series of mixed dopamine D2/D4 receptor antagonists. To further the structure-activity relationship (SAR) study, 3-piperazinylindolin-2-ones (gamma-lactams) and 3-piperazinyl-3H,4H,5H-benzo[f]azepin-2-ones (epsilon-lactams) were also prepared and examined.

Phenyloxazoles and phenylthiazoles as benzamide bioisosteres: synthesis and dopamine receptor binding profiles

Conformationally restricted benzamide bioisosteres were investigated when the aminomethylpyrrolidine derivative 4o proved D3 as well as D4 binding properties which were comparable to those of the atypical neuroleptics sulpiride and clozapine, respectively.

SPECT imaging with the D(4) receptor antagonist L-750,667 in nonhuman primate brain

The suitability of an (123)I-labeled form of the putative D(4) receptor ligand L750,667 as a radiotracer for single photon emission computed tomography imaging was assessed in nonhuman primates. [(123)I]L750,667, labeled by iododestannylation, was administered to baboons in bolus and bolus plus constant infusion paradigms and imaged for 6 h. Total [(123)I]L750,667 brain uptake peaked (2.3% injected dose) at 15 min postinjection. [(123)I]L750,667 uptake was observed in all brain regions measured including diencephalon, brainstem, basal ganglia, cingulate cortex, and cerebellum, and slightly lower levels were noted in the frontal, parietal, temporoinsular, and occipital cortices. Administration of the D(4) receptor antagonist NGD 94-1 (2 mg/kg) did not displace radioactivity from any of the brain regions examined. Thus, while L750,667 is selective for the D(4) receptor in vitro, because brain [(123)I]L750,667 uptake was not displaced by NGD 94-1 at receptor saturating doses, [(123)I]L750,667 does not appear to be a suitable radiotracer for in vivo imaging of the D(4) receptor.

Dopamine D4 receptors

Initial investigations on dopamine D4 receptors generated much interest in the role of this receptor in schizophrenia and other aspects of human behavior, as well as new opportunities for novel therapeutics. However, attempts to treat patients suffering from schizophrenia with dopamine D4 agents have failed to yield satisfactory results so far. An examination of the dopamine D4 literature shows that contrasting and conflicting data seemed to be the norm in this field of research. This paper reviews the literature on the dopamine D4 receptor and discusses many of the associated methodological problems that might have contributed to the paradoxical findings.

A series of 6- and 7-piperazinyl- and -piperidinylmethylbenzoxazinones with dopamine D4 antagonist activity: discovery of a potential atypical antipsychotic agent

As part of a program to develop dopamine D4 antagonists for the treatment of schizophrenia, we discovered a series of 6- and 7-(phenylpiperazinyl)- and -(phenylpiperidinyl)methylbenzoxazinones through mass screening of our compound library. A structure-activity relationship SAR study was carried out involving substituents on the phenyl ring, and several selective D4 antagonists were identified. The 7-substituted benzoxazinones showed more activity in neurochemical and behavioral tests than the 6-substituted series. One of the most potent and selective compounds (26) was found to have potent activity in animal tests predictive of antipsychotic activity in humans after oral administration. This paper describes the SAR of the benzoxazinone series and the preclinical characterization of 26.

Piperidinylpyrroles: design, synthesis and binding properties of novel and selective dopamine D4 receptor ligands

Piperidinylpyrroles of type 3 were synthesized through a modified Paal-Knorr reaction. For the introduction of pyrrole-substituents high yielding transformations including Sonogashira cross-coupling reactions were utilized. Employment of the reagent TosMIC gave access to the regioisomeric oxazolyl derivatives 7 and 11 which showed the highest dopamine D4 receptor binding of the series investigated.

Synthesis and dopamine D2-like receptor binding affinity of substituted 5-phenyl-pyrrole-3-carboxamides

A series of 5-p-substituted phenyl-pyrrole-3-carboxamide derivatives was designed as hybrid analogs of the dopamine D2-like 5-phenyl-pyrrole and heterocyclic carboxamide antipsychotics. The title compounds were synthesized and evaluated for dopamine D2-like receptor by means of [3H]YM-09151-2 receptor binding assay. The compound bearing a 1-ethyl-2-methyl-pyrrolidine moiety as the basic part of 5-phenyl-pyrrole-3-carboxamide derivative 1a together with its 2-chloro analog 1f were found to possess affinity in the low micromolar range. Substituted phenyl-pyrrolecarboxamides containing groups such as F, Cl, NO2, CH3, at the 4-position of the phenyl ring, gave ligands with lower D2-like affinity.

2,2-Dicyanovinyl as a nonaromatic aryl bioisostere: synthesis, binding experiments and SAR studies of highly selective dopamine D4 receptor ligands

The phenylpiperazinylmethyl substituted pyrrolylmethylenemalononitriles of type 3 and 4 were synthesized and evaluated as strong and selective dopamine D4 receptor ligands.

1-(3-Cyanobenzylpiperidin-4-yl)-5-methyl-4-phenyl-1, 3-dihydroimidazol-2-one: a selective high-affinity antagonist for the human dopamine D(4) receptor with excellent selectivity over ion channels

After the requirement of pseudocycle formation in the ureas 3 and 7 for hD(4) binding and selectivity was confirmed, structural hybridization with the known hD(4) ligand 2 led to the design and identification of the lead 4-(2-oxo-1, 3-dihydroimidazol-2-yl)piperidine 8. Optimization studies were carried out on 8 with the aim of achieving 1000-fold selectivity for hD(4) over all other receptors while retaining the good pharmacokinetic properties of the lead. After initial preparation of 8 as a minor component in a low-yielding reaction, a novel and regioselective "four-step/one-pot" procedure was developed which proved to be applicable to rapid investigation of the SAR of the 1, 3-dihydroimidazol-2-one ring. Various changes to substituents attached to the 3-, 4-, or 5-position of the 1, 3-dihydroimidazol-2-one core of 8 did not significantly improve selectivity for hD(4) over hD(2) and hD(3). Greater selectivity (>1000-fold) was ultimately achieved by meta substitution of the benzyl group of 8 with various substituents. Compounds 28, 31, and 32 all possess the required selectivity for hD(4) over the other dopamine subtypes, but only 32 has >1000-fold selectivity over all the key counterscreens we tested against. Compound 32 is an antagonist at hD(4) and has a good pharmacokinetic profile in the rat, with excellent estimated in vivo receptor occupancy, thus making it a potentially useful pharmacological tool to investigate the role of the D(4) receptor.

SAR of novel biarylmethylamine dopamine D4 receptor ligands

SAR for a novel series of dopamine D4 receptor ligands is shown. Very selective, highly potent compounds like 1-(2-pyrimidinyl)-4-(3-(3-thienyl)-benzyl)-piperazine (5f) and 2-(4-(1-fluorenylmethyl)-1-piperazinyl)-pyrimidine (8c) were obtained.