D4/5-HT2A Receptor antagonists: LU-111995 and other potential new antipsychotics in development

Design, synthesis and dopamine D4 receptor binding activities of new N-heteroaromatic 5/6-ring Mannich bases

A series of phenylpiperazine-methyl-substituted 1H-pyrrolo[2,3-c]pyridine, imidazo[1,2-c]-, pyrrolo[2,3-d]- and pyrrolo[3,2-d]pyrimidines were prepared as selective dopamine D4-ligands. The pyrrolo[2,3-d]pyrimidine derivatives 12d (K(i)=1,9 nM) and 34 d (K(i)=2,4 nM) as well as the pyrrolo[3,2-d]pyrimidine Mannich base 49f (K(i)=2,8 nM) showed high dopamine D4 receptor activity superior to the atypical antipsychotic agent clozapine.

N-[(3S)-1-Benzylpyrrolidin-3-yl]-(2-thienyl)benzamides: Human dopamine D4 ligands with high affinity for the 5-HT2A receptor

A series of N-[(3S)-1-benzylpyrrolidin-3-yl]-(2-thienyl)benzamides 8 has been prepared and found to bind with high affinity to the human D(4) (hD(4)) and 5-HT(2A) receptors. Several compounds displayed selectivity for these receptors versus hD(2) and alpha(1) adrenergic receptors of over 500-fold.

Synthesis and functional activity of (2-aryl-1-piperazinyl)-N-(3-methylphenyl)acetamides: selective dopamine D4 receptor agonists

Diaryl piperazine acetamides were identified as potent and selective dopamine D(4) receptor agonists. Our strategy is based on an amide bond reversal of an acid sensitive, dopamine D(4) receptor partial agonist, PD 168077. This reversal provided compounds with excellent potency and improved stability. Systematic evaluation of the substitution on the aryl piperazine portion revealed a significant effect on functional activity. The synthesis and biological activity of these new dopamine D(4) agonists is discussed.

Dopamine D4 Ligands and Models of Receptor Activation: 2-(4-Pyridin-2-ylpiperazin-1-ylmethyl)-1H-benzimidazole and Related Heteroarylmethylarylpiperazines Exhibit a Substituent Effect Responsible for Additional Efficacy Tuning

A series of subtype selective dopamine D(4) receptor ligands from the hetroarylmethylphenylpiperazine class have been discovered that exhibit a remarkable structure-activity relationship (SAR), revealing a substituent effect in which regiosubstitution on the terminal arylpiperazine ring can modulate functional or intrinsic activity. Other structure-dependent efficacy studies in the dopamine D(4) field have suggested a critical interaction of the heteroarylmethyl moiety with specific protein microdomains in controlling intrinsic activity. Our studies indicate that for some binding orientations, the phenylpiperazine moiety also plays a key role in determining efficacy. These data also implicate a kinetic or efficiency term, contained within measured functional affinities for agonists, which support a sequential binding and conformational stabilization model for receptor activation. The structural similarity between partial agonist and antagonist, within this subset of ligands, and lack of bioisosterism for this substituent effect are key phenomena for these hypotheses.

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.

The psychopharmacology-molecular biology interface: exploring the behavioural roles of dopamine receptor subtypes using targeted gene deletion ('knockout')

In the absence of selective agonists and antagonists able to discriminate between individual members of the D1-like and D2-like families of dopamine receptor subtypes, functional parcellation has remained problematic. 'Knockout' of these subtypes by targeted gene deletion offers a new approach to evaluating their roles in the regulation of behaviour. Like any new technique, 'knockout' has associated with it a number of methodological limitations that are now being addressed in a systematic manner. Studies on the phenotype of D1(A/1), D(1B/5), D2, D3 and D4 'knockouts' at the level of spontaneous and agonist/antagonist-induced behaviour are reviewed, in terms of methodological issues, neuronal implications and potential clinical relevance. Dopamine receptor subtype 'knockout' is a nascent technology that is now beginning to fulfil its potential. It is being complemented by more systematic phenotypic characterisation at the level of behaviour and additional, molecular biologically-based approaches.

Conformationally constrained butyrophenones with affinity for dopamine (D(1), D(2), D(4)) and serotonin (5-HT(2A), 5-HT(2B), 5-HT(2C)) receptors: synthesis of aminomethylbenzo[b]furanones and their evaluation as antipsychotics

A series of novel conformationally restricted butyrophenones (6-aminomethyl-4,5,6,7-tetrahydrobenzo[b]furan-4-ones bearing 4-(6-fluorobenzisoxazolyl)piperidine, 4-(p-fluorobenzoyl)piperidine, 4-(o-methoxyphenyl)piperazine, 4-(2-pyridyl)piperazine, 4-(2-pyrimidinyl)piperazine, or linear butyro(or valero)phenone fragments) were prepared and evaluated as antipsychotic agents by in vitro assays for affinity for dopamine receptors (D(1), D(2), D(4)) and serotonin receptors (5-HT(2A), 5-HT(2B), 5-HT(2C)), by neurochemical studies, and by in vivo assays for antipsychotic potential and the risk of inducing extrapyramidal side effects. Potency and selectivity depended mainly on the amine fragment connected to the cyclohexanone structure. Compounds 20b, with a benzoylpiperidine moiety, and 20c, with a benzisoxazolyl fragment, were selective for 5-HT(2A) receptors. The in vitro and in vivo pharmacological profiles of N-[(4-oxo-4,5,6, 7-tetrahydrobenzo[b]furan-6-yl)methyl]-4-(p-fluorobenzoyl)piperidine (20b, QF1003B) and N-[(4-oxo-4,5,6, 7-tetrahydrobenzo[b]furan-6-yl)methyl]-4-(6-fluorobenzisoxazol-3-yl)p iperidine (20c, QF1004B) suggest that they may be effective as antipsychotic (neuroleptic) drugs.

Dopamine D4 receptors and development of newer antipsychotic drugs

The last ten years have witnessed the generation of a large amount of information on the neurobiology of dopamine receptors. Molecular biology and pharmacology studies have revealed existence of at least five dopamine receptor subtypes, namely D1, D2, D3, D4 and D5. The discovery of D4 receptors and the putative affinity of clozapine for D4 receptors have kindled development of selective D4 receptor antagonists for the treatment of schizophrenia. Studies on expression of D4 receptor proteins have shown selective localisation of D4 receptors in mesolimbic/mesocortical areas which could probably explain the lack of motor side effects with atypical antipsychotics like clozapine and olanzapine. However, neuropathological and genetic studies on the role of D4 receptors in the pathophysiology of schizophrenia and preliminary clinical studies with selective D4 receptor antagonists have been disappointing. There have been, however, complimentary findings between selective D4 receptor antagonism and genetic approaches such as antisense treatment or gene targeting. The therapeutic potential of D4 receptors as a target for developing antipsychotics will be known only when selective D4 receptor-antagonists with varying D2/D4 and D4/5-HT2A ratios are developed and tested in psychiatric patients.

Azaindole derivatives with high affinity for the dopamine D4 receptor: synthesis, ligand binding studies and comparison of molecular electrostatic potential maps

Piperazinylmethyl substituted pyrazolo[1,5-a]pyridines and related heterocycles were synthesized and found to recognize selectively the dopamine D4 receptor. For the most potent derivative 10d a Ki value of 2.0 nM was observed. SAR studies including the comparison of molecular isopotential surfaces were performed.