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

G protein-coupled receptors in neurodegenerative diseases and psychiatric disorders

Neuropsychiatric disorders are multifactorial disorders with diverse aetiological factors. Identifying treatment targets is challenging because the diseases are resulting from heterogeneous biological, genetic, and environmental factors. Nevertheless, the increasing understanding of G protein-coupled receptor (GPCR) opens a new possibility in drug discovery. Harnessing our knowledge of molecular mechanisms and structural information of GPCRs will be advantageous for developing effective drugs. This review provides an overview of the role of GPCRs in various neurodegenerative and psychiatric diseases. Besides, we highlight the emerging opportunities of novel GPCR targets and address recent progress in GPCR drug development.

From Peptides to Peptidomimetics: A Strategy Based on the Structural Features of Cyclopropane

Peptidomimetics, non-natural mimicries of bioactive peptides, comprise an important class of drug molecules. The essence of the peptidomimetic design is to mimic the key conformation assumed by the bioactive peptides upon binding to their targets. Regulation of the conformation of peptidomimetics is important not only to enhance target binding affinity and selectivity, but also to confer cell-membrane permeability for targeting protein-protein interactions in cells. The rational design of peptidomimetics with suitable three-dimensional structures is challenging, however, due to the inherent flexibility of peptides and their dynamic conformational changes upon binding to the target biomolecules. In this Minireview, a three-dimensional structural diversity-oriented strategy based on the characteristic structural features of cyclopropane to address this challenging issue in peptidomimetic chemistry is described.

Chemoselective and stereoselective lithium carbenoid mediated cyclopropanation of acyclic allylic alcohols

A new method for the chemo- and stereoselective conversion of acyclic allylic alcohols into the corresponding substituted cyclopropane derivatives has been developed using lithium carbenoids.

Piperazine scaffold: A remarkable tool in generation of diverse pharmacological agents

Piperazine is one of the most sought heterocyclics for the development of new drug candidates. This ring can be traced in a number of well established, commercially available drugs. Wide array of pharmacological activities exhibited by piperazine derivatives have made them indispensable anchors for the development of novel therapeutic agents. The review herein highlights the therapeutic significance of piperazine derivatives. Various therapeutically active piperazine derivatives developed by several chemists are reported here.

Conformational restriction approach to β-secretase (BACE1) inhibitors III: effective investigation of the binding mode by combinational use of X-ray analysis, isothermal titration calorimetry and theoretical calculations

For further investigation of BACE1 inhibitors using conformational restriction with sp(3) hybridized carbon, we applied this approach to 6-substituted aminopyrimidone derivatives 3 to improve the inhibitory activity by reducing the entropic energy loss upon binding to BACE1. Among eight stereoisomers synthesized, [trans-(1'R,2'R),6S] isomer 6 exhibited the best BACE1 inhibitory activity, which was statistically superior to that of the corresponding ethylene linker compound (R)-3. Combinational examinations of the binding mode of 6 were performed, which included isothermal titration calorimetry (ITC), X-ray crystallographic structure analysis and theoretical calculations, to clarify the effect of our conformational restriction approach. From the ITC measurement, the binding entropy of 6 was found to be ∼0.5kcal larger than that of (R)-3, which is considered to be affected by conformational restriction with a cyclopropane ring.

Synthesis and dopaminergic activity of some E-3-(piperidin-1-yl)-1-(4-substituted phenyl)prop-2-en-1-one derivatives

A convenient route for the synthesis of some 2-propen-1-one derivatives with E isomeric configuration is described. The activity of the synthesized compounds was evaluated through behavioral studies of apomorphine-induced licking in animal models. It was demonstrated that most of the synthesized compounds showed moderate activity in inhibition of lickings, among which 6a, was the most active compound at 30 mg/kg.

Selective 5-hydroxytryptamine 2C receptor agonists derived from the lead compound tranylcypromine: identification of drugs with antidepressant-like action

We report here the design, synthesis, and pharmacological properties of a series of compounds related to tranylcypromine (9), which itself was discovered as a lead compound in a high-throughput screening campaign. Starting from 9, which shows modest activity as a 5-HT(2C) agonist, a series of 1-aminomethyl-2-phenylcyclopropanes was investigated as 5-HT(2C) agonists through iterative structural modifications. Key pharmacophore feature of this new class of ligands is a 2-aminomethyl-trans-cyclopropyl side chain attached to a substituted benzene ring. Among the tested compounds, several were potent and efficacious 5-HT(2C) receptor agonists with selectivity over both 5-HT(2A) and 5-HT(2B) receptors in functional assays. The most promising compound is 37, with 120- and 14-fold selectivity over 5-HT(2A) and 5-HT(2B), respectively (EC(50) = 585, 65, and 4.8 nM at the 2A, 2B, and 2C subtypes, respectively). In animal studies, compound 37 (10-60 mg/kg) decreased immobility time in the mouse forced swim test.

1-Cinnamyl-4-(2-methoxyphenyl)piperazines: Synthesis, Binding Properties, and Docking to Dopamine (D2) and Serotonin (5-HT1A) Receptors

Clinical properties of atypical antipsychotics are based on their interaction with D(2) dopamine receptor and serotonin 5-HT(1A) and 5-HT(2A) receptors. As a part of our research program on new antipsychotics, we synthesized various derivatives of 1-cinnamyl-4-(2-methoxyphenyl)piperazines, and evaluated their affinities for D(2), 5-HT(1A), 5-HT(2A), and adrenergic (alpha(1)) receptors using radioligand-binding assays. In addition, we performed docking analysis using models for the D(2) and 5-HT(1A) receptors. All compounds exhibited low to moderate affinity to 5-HT(1A) and 5-HT(2A) receptors, high affinity to the D(2 )receptor and large variability in affinities for the alpha(1) receptor. Docking analysis indicated that the binding to D(2) and 5-HT(1A) receptors is based on (i) interaction between protonated N1 of the piperazine ring and various aspartate residues, (ii) hydrogen bonds between various moieties of the ligand and the residues of threonine, serine, histidine or tryptophane, and (iii) edge-to-face interactions of the aromatic ring of the arylpiperazine moiety with phenylalanine or tyrosine residues. Docking data for the D(2) receptor can account for the binding properties obtained in binding assays, suggesting that the model is reliable and robust. However, docking data for the 5-HT(1A) receptor cannot account for actual binding properties, suggesting that further refinement of the model is required.

Effects of topiramate on the prepulse inhibition of the acoustic startle in rats

The anticonvulsant topiramate (TPM) has been recently proposed as a novel adjuvant therapy for bipolar disorder and schizophrenia, yet its efficacy remains controversial. As both disorders are characterized by gating deficits, we tested the effects of TPM on the behavioral paradigm of prepulse inhibition (PPI) of the acoustic startle response, a validated animal model of sensorimotor gating. TPM (10, 18, 32, 58, 100 mg/kg, intraperitoneal, i.p.) enhanced PPI in rats in a dose-dependent fashion, prevented the PPI reduction mediated by the dopaminergic agonist apomorphine (0.25 mg/kg, subcutaneous, s.c.) and potentiated the effects of the antipsychotic drugs haloperidol (0.05, 0.1 mg/kg, i.p.) and clozapine (2.5, 5 mg/kg, i.p.). Conversely, TPM elicited no significant effect on the PPI disruption mediated by the NMDA receptor antagonist dizocilpine (0.05, 0.1 mg/kg, s.c.) and surprisingly antagonized the attenuation of dizocilpine-induced PPI disruption mediated by clozapine (5 mg/kg, i.p.). Our results suggest that TPM may exert diverse actions on the neural substrates of sensorimotor gating. While the pharmacological mechanisms of such effects are still elusive, our findings might contribute to shed light on some controversies on the therapeutic action of TPM, and point to this drug as a putative novel adjuvant therapy for some clusters of gating disturbances.

Optical resolution methods

Despite the large number of elaborate enantioselective syntheses for the preparation of a single enantiomer to achieve industrial and scientific goals, the separation and purification of enantiomers (components of racemic compounds) is also necessary. Hence, we present the most often used thought-provoking modern methods based on momentous recognitions (e.g. spontaneous resolution, induced crystallization, resolution by formation of diastereomers, resolution by formation of non-covalent diastereomers, resolution by diastereomeric salt formation, resolution by diastereomeric complex formation, "half equivalent" methods of resolution, separation by crystallization, separation by distillation, separation by supercritical fluid extraction, resolution with mixtures of resolving agents, resolution with a derivative of the target compound, enantioselective chromatography, resolution by formation of covalent diastereomers, resolution by substrate selective reaction, kinetic resolution without enzymes, kinetic resolution by enzyme catalysis, hydrolytic and redox enzymes, kinetic and thermodynamic control, resolutions combined with 2nd order asymmetric transformations, enrichment of partially resolved mixtures, role of the solvent and methods of optimization in the separation of diastereoisomers, non-linear effects and selected examples of resolution on an industrial scale).

Highly Efficient Stereoconservative Amidation and Deamidation of α-Amino Acids

[reaction: see text] An overall stereoconservative protection and deprotection method of amino and carboxyl groups is presented. N-Phthaloyl N'-alkyl secondary amides of alpha-amino acids can be generated from corresponding N-phthaloyl amino acids by coupling reaction of N-alkylamines using mixed anhydride method. These secondary amides can be transformed by thermal rearrangement of intermediate nitrosoamides to O-alkyl esters with retention of configuration and excellent yields.

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.

Synthesis of derivatives of (1S,2R)-1-phenyl-2-[(S)-1-aminopropyl]-N,N-diethylcyclopropanecarboxamide (PPDC) modified at the 1-aromatic moiety as novel NMDA receptor antagonists: the aromatic group is essential for the activity

(1S,2R)-1-Phenyl-2-[(S)-1-aminopropyl]-N,N-diethylcyclopropanecarboxamide (PPDC, 4a), which is a conformationally restricted analogue of antidepressant milnacipran [(+/-)-1], is a new class of potent noncompetitive NMDA receptor antagonists. A series of PPDC analogues modified at the 1-phenyl moiety, that is, the analogue 6 lacking 1-phenyl group, the 1-(fluorophenyl) analogues 4b,c,d, the 1-(methylphenyl) analogues 4e-g and the 1-(naphthyl) analogues 4h,i were synthesized. Analogue 6, lacking the 1-phenyl group, was completely inactive showing that the aromatic moiety is essential for the NMDA receptor binding. Among the analogues synthesized, the 1-o-fluorophenyl and 1-m-fluorophenyl analogues 4b and 4c showed potent affinities for the NMDA receptor [IC(50)=0.16+/-0.001 microM (4b), 0.15+/-0.02 microM (4c)], which were improved to some extent compared to those of the parent compound PPDC (IC(50)=0.20+/-0.02 microM). On the other hand, compounds 4b and 4c showed none of the 5-HT-uptake inhibitory effect, while PPDC turned out to be a weak 5-HT-uptake inhibitor.

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.

Indoline and piperazine containing derivatives as a novel class of mixed D(2)/D(4) receptor antagonists. Part 2: asymmetric synthesis and biological evaluation

A series of chiral benzylpiperazinyl-1-(2,3-dihydro-indol-1-yl)ethanone derivatives were prepared and examined for their affinity at dopamine D(2) and D(4) receptors. Three compounds having D(2)/D(4) affinity ratios approximating that found for the atypical neuroleptic clozapine were further evaluated in behavioral tests of antipsychotic efficacy and motor side effects.