SAR of novel biarylmethylamine dopamine D4 receptor ligands

[Pd(Cl)2{P(NC5H10)(C6H11)2}2]--a highly effective and extremely versatile palladium-based Negishi catalyst that efficiently and reliably operates at low catalyst loadings

[Pd(Cl)(2){P(NC(5)H(10))(C(6)H(11))(2)}(2)] (1) has been prepared in quantitative yield by reacting commercially available [Pd(cod)(Cl)(2)] (cod=cyclooctadiene) with readily prepared 1-(dicyclohexylphosphanyl)piperidine in toluene under N(2) within a few minutes at room temperature. Complex 1 has proved to be an excellent Negishi catalyst, capable of quantitatively coupling a wide variety of electronically activated, non-activated, deactivated, sterically hindered, heterocyclic, and functionalized aryl bromides with various (also heterocyclic) arylzinc reagents, typically within a few minutes at 100 °C in the presence of just 0.01 mol% of catalyst. Aryl bromides containing nitro, nitrile, ether, ester, hydroxy, carbonyl, and carboxyl groups, as well as acetals, lactones, amides, anilines, alkenes, carboxylic acids, acetic acids, and pyridines and pyrimidines, have been successfully used as coupling partners. Furthermore, electronic and steric variations are tolerated in both reaction partners. Experimental observations strongly indicate that a molecular mechanism is operative.

SAR Study of 1-Aryl-4-(phenylarylmethyl)piperazines as Ligands for Both Dopamine D2 and Serotonin 5-HT1A Receptors Showing Varying Degrees of (Ant)agonism. Selection of a Potential Atypical Antipsychotic

The syntheses of several 1-aryl-4-(arylpyridylmethyl)piperazines (4) and their affinities for dopamine D(2) and serotonin 5-HT(1A) receptors are described. The compounds were evaluated both in vitro and in vivo, resulting in the identification of the drug candidate SLV313 (4e) with equipotent and full D(2) receptor antagonism and 5-HT(1A) receptor agonism. Minor structural modifications in SLV313 revealed the possibility of designing compounds possessing varying degrees of partial agonism on one or both target receptors.

1H-Pyrazolo-[3,4-c]cyclophepta[1,2-c]thiophenes: A unique structural class of dopamine D4 selective ligands

A series of novel 1H-pyrazolo-[3,4-c]cyclophepta[1,2-c]thiophenes was prepared and screened at selected dopamine receptor subtypes. Compound 4 (NGB 4420) displayed high affinity and selectivity (>100-fold) for the D(4) over D(2) and other CNS receptors. This compound was identified as a D(4) antagonist via its attenuation of dopamine agonist-induced GTPgamma(35)S binding at D(4) receptor.

Indoline and piperazine containing derivatives as a novel class of mixed D(2)/D(4) receptor antagonists. Part 1: identification and structure-activity relationships

Optimization of the lead compound 2-[-4-(4-chloro-benzyl)-piperazin-1-yl]-1-(2,3-dihydro-indol-1-yl)-ethanone 1 by systematic structure-activity relation (SAR) studies lead to two potent compounds 2-[-4-(4-chloro-benzyl)-piperazin-1-yl]-1-(2-methy-2,3-dihydro-indol-1-yl)-ethanone 2n and 2-[-4-(4-chloro-benzyl)-piperazin-1-yl]-1-(2-methy-2,3-dihydro-indol-1-yl)-ethanone 7b. Their related synthesis was also reported.

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.

The dopamine D(4) receptor: one decade of research

Dopamine is an important neurotransmitter involved in motor control, endocrine function, reward, cognition and emotion. Dopamine receptors belong to the superfamily of G protein-coupled receptors and play a crucial role in mediating the diverse effects of dopamine in the central nervous system (CNS). The dopaminergic system is implicated in disorders such as Parkinson's disease and addiction, and is the major target for antipsychotic medication in the treatment of schizophrenia. Molecular cloning studies a decade ago revealed the existence of five different dopamine receptor subtypes in mammalian species. While the presence of the abundantly expressed dopamine D(1) and D(2) receptors was predicted from biochemical and pharmacological work, the cloning of the less abundant dopamine D(3), D(4) and D(5) receptors was not anticipated. The identification of these novel dopamine receptor family members posed a challenge with respect to determining their precise physiological roles and identifying their potential as therapeutic targets for dopamine-related disorders. This review is focused on the accomplishments of one decade of research on the dopamine D(4) receptor. New insights into the biochemistry of the dopamine D(4) receptor include the discovery that this G protein-coupled receptor can directly interact with SH3 domains. At the physiological level, converging evidence from transgenic mouse work and human genetic studies suggests that this receptor has a role in exploratory behavior and as a genetic susceptibility factor for attention deficit hyperactivity disorder.

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.

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.

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.