Investigation of various N-heterocyclic substituted piperazine versions of 5/7-{[2-(4-aryl-piperazin-1-yl)-ethyl]-propyl-amino}-5,6,7,8-tetrahydro-naphthalen-2-ol: Effect on affinity and selectivity for dopamine D3 receptor

Here we report on the design and synthesis of several heterocyclic analogues belonging to the 5/7-{[2-(4-aryl-piperazin-1-yl)-ethyl]-propyl-amino}-5,6,7,8-tetrahydro-naphthalen-2-ol series of molecules. Compounds were subjected to [³H]spiperone binding assays, carried out with HEK-293 cells expressing either D2 or D3 dopamine receptors, in order to evaluate their inhibition constant (K_i) at these receptors. Results indicate that N-substitution on the piperazine ring can accommodate various substituted indole rings. The results also show that in order to maintain high affinity and selectivity for the D3 receptor the heterocyclic ring does not need to be connected directly to the piperazine ring as the majority of compounds included here are linked either via an amide or a methylene linker to the heterocyclic moiety. The enantiomers of the most potent racemic compound 10e exhibited differential activity with (?)-10e (K_i; D2 = 47.5 nM, D3 = 0.57 nM) displaying higher affinity at both D2 and D3 receptors compared to its enantiomer (+)-10e (K_i; D2 = 113 nM, D3 = 3.73 nM). Additionally, compound (?)-10e was more potent and selective for the D3 receptor compared to either 7-OH-DPAT or 5-OH-DPAT. Among the bioisosteric derivatives, the indazole derivative 10g and benzo[b]thiophene derivative 10i exhibited the highest affinity for D2 and D3 receptors. In the functional GTPγS binding study, one of the lead molecules, (?)-15, exhibited potent agonist activity at both D2 and D3 receptors with preferential affinity at D3.     

Interactions of N-{[2-(4-phenyl-piperazin-1-yl)-ethyl]-phenyl}-2-aryl-2-yl-acetamides and 1-{[2-(4-phenyl-piperazin-1-yl)-ethyl]-phenyl}-3-aryl-2-yl-ureas with dopamine D2 and 5-hydroxytryptamine 5HT(1A) receptors

It is suggested that the ratio of dopamine D(2) to 5-hydroxytryptamine 5-HT(1A) activity is an important parameter that determines the efficiency of antipsychotic drugs. Here we present the synthesis of N-{[2-(4-phenyl-piperazin-1-yl)-ethyl]-phenyl}-2-aryl-2-yl-acetamides and 1-{[2-(4-phenyl-piperazin-1-yl)-ethyl]-phenyl}-3-aryl-2-yl-ureas and their structure-activity relationship studies on dopamine D(2) and 5-hydrohytryptamine 5-HT(1A) receptors. It was shown that ligand selectivity and affinity strongly depends on their topology and the presence of a pyridyl group in the head of molecules. Molecular modeling studies using homology modeling and docking simulation revealed a rational explanation for the ligand behavior. The observed binding modes and receptor-ligand interactions provided us with a clue for optimizing the optimal selectivity towards 5-HT(1A) receptors.     

Design, synthesis and biological activity of novel dimethyl-[2-[6-substituted-indol-1-yl]-ethyl]-amine as potent, selective, and orally-bioavailable 5-HT(1D) agonists

A novel series of highly potent human 5-HT_1D agonists, dimethyl-{2-[6-substituted-indol-1-yl]-ethyl}-amine, was synthesized. Structure–activity relationship (SAR) investigation revealed 4-[1-(2-dimethylamino-ethyl)-1H-indol-6-yl]-tetrahydro-thiopyran-4-ol, 11b (ALX-2732), as a potent (K_i=2.4 nM) agonist at the human 5-HT_1D receptor with good selectivity over the other serotonin receptor subtypes. This compound demonstrated favorable in vitro metabolic stability in human and rat liver microsomes and was found to be orally bioavailable in rats (F_po=51%).     

Optically active antifungal azoles: synthesis and antifungal activity of (2R,3S)-2-(2,4-difluorophenyl)-3-(5-[2-[4-aryl-piperazin-1-yl]-ethyl]-tetrazol-2-yl/1-yl)-1-[1,2,4]-triazol-1-yl-butan-2-ol

A series of (2R,3S)-2-(2,4-difluorophenyl)-3-(5-[2-[4-aryl-piperazin-1-yl]-ethyl]-tetrazol-2-yl)-1-[1,2,4]-triazol-1-yl-butan-2-ol (11a-n) and (2R,3S)-2-(2,4-difluorophenyl)-3-(5-[2-[4-aryl-piperazin-1-yl]-ethyl]-tetrazole-1-yl)-1-[1,2,4]-triazol-1-yl-butan-2-ol (12a-n) has been synthesized. The antifungal activity of compounds was evaluated by in vitro agar diffusion and broth dilution assay. Compounds 11d and its positional isomer 12d having 3-trifluoromethyl substitution on the phenyl ring of piperazine demonstrated significant antifungal activity against variety of fungal cultures (Candida spp. C. neoformans and Aspergillus spp.). The compound 12d showed MIC value of 0.12 microg/mL for C. albicans, C. albicans V-01-191A-261 (resistant strain); 0.25 microg/mL for C. tropicalis, C. parapsilosis ATCC 22019 and C. krusei and MIC value of 0.5 microg/mL for C. glabrata, C. krusei ATCC 6258, which is comparable to itraconazole and better than fluconazole. Further, compound 11d showed significant activity (MIC; 0.25-0.5 microg/mL) against Candida spp. and strong anticryptococcal activity (MIC; 0.25 microg/mL) against C. neoformans.     

Further delineation of hydrophobic binding sites in dopamine D2/D3 receptors for N-4 substituents on the piperazine ring of the hybrid template 5/7-{[2-(4-aryl-piperazin-1-yl)-ethyl]-propyl-amino}-5,6,7,8-tetrahydro-naphthalen-2-ol

Here we report a structure–activity relationship (SAR) study of analogues of 5/7-{[2-(4-aryl-piperazin-1-yl)-ethyl]-propyl-amino}-5,6,7,8-tetrahydro-naphthalen-2-ol. Our SAR is focused on introduction of various substitutions in the piperazine ring of the hybrid template. The goal behind this study is to delineate the nature of the binding pocket for N-aryl substitution in the piperazine ring by observing the effect of various hydrophobic and other heteroaromatic substitutions on binding affinity (K_i), as measured with tritiated spiperone and HEK-293 cells expressing either D₂ or D₃ receptors. Functional activity of selected compounds was assessed with the GTPγS binding assay. Compound 8d was the most selective for the D₃ receptor in the spiperone binding assay. An interesting similarity in binding affinity was observed between isoquinoline derivative D-301 and the 2-substituted pyridine derivative 8d, suggesting the importance of relative spatial relationships between the N-atom of the ligand and the molecular determinants of the binding pocket in D₂/D₃ receptors. Functional activity assays demonstrated high potency and selectivity of (+)-8a and (?)-28b (D₂/D₃ (ratio of EC₅₀): 105 and 202, respectively) for the D₃ receptor and both compounds were more selective compared to the reference drug ropinirole (D₂/D₃ (ratio of EC₅₀): 29.5).     

(S)-N-[1-(4-cyclopropylmethyl-3,4-dihydro-2H-benzo[1,4]oxazin-6-yl)-ethyl]-3-(2-fluoro-phenyl)-acrylamide is a potent and efficacious KCNQ2 opener which inhibits induced hyperexcitability of rat hippocampal neurons

(S)-N-[1-(4-Cyclopropylmethyl-3,4-dihydro-2H-benzo[1,4]oxazin-6-yl)-ethyl]-3-(2-fluoro-phenyl)-acrylamide ((S)-2) was identified as a potent and efficacious KCNQ2 opener. This compound demonstrated significant activity in reducing neuronal hyperexcitability in rat hippocampal slices, and the inhibition mediated by (S)-2 was reversed by the KCNQ blocker linopirdine.     

Synthesis and KCNQ2 opener activity of N-(1-benzo[1,3]dioxol-5-yl-ethyl, N-[1-(2,3-dihydro-benzofuran-5-yl)-ethyl, and N-[1-(2,3-dihydro-1H-indol-5-yl)-ethyl acrylamides

Bioisosteric replacement studies led to the identification of N-(1-benzo[1,3]dioxol-5-yl-ethyl)-3-(2-chloro-phenyl)-acrylamide ((S)-3) as a highly potent KCNQ2 opener, and 3-(2,6-difluoro-phenyl)-N-[1-(2,3-dihydro-benzofuran-5-yl)-ethyl]-acrylamide ((S)-4), and N-[1-(2,3-dihydro-1H-indol-5-yl)-ethyl]-3-(2-fluoro-phenyl)-acrylamide ((S)-5) as highly efficacious KCNQ2 openers. In contrast, their respective R enantiomers showed significantly less or no appreciable KCNQ2 opener activity even at the highest concentration tested (10 microM). Because of its high potency and moderate efficacy as well as its convenient synthesis, (+/-)-3 was selected as a reference compound for analyzing efficacies of KCNQ openers in electrophysiology studies. Compounds (S)-4 and (S)-5 demonstrated significant activity in reducing neuronal hyperexcitability in rat hippocampal slices. The synthesis and the KCNQ2 opener activity of these acrylamides are described.     

Effect of 7-(3-[4-(2,3-dimethylphenyl)piperazinyl]propoxy)- 2(1H)-quinolinone (OPC-4392), a newly synthesized agonist for presynaptic dopamine D2 receptor, on tyrosine hydroxylation in rat striatal slices

The effects of a newly synthesized compound, 7-(3-[4-(2,3-dimethylphenyl)piperazinyl]propoxy)-2(1H)-quinolinone (OPC-4392), on tyrosine hydroxylation in situ and in vitro were studied using rat striatal slices and tyrosine hydroxylase (TH) purified from bovine adrenal medulla, respectively. OPC-4392 dose-dependently inhibited L-dihydroxyphenylalanine (DOPA) formation in rat striatal slices with IC50 values of about 10(-6) M. The inhibitory effect of OPC-4392 on in situ DOPA formation was dose-dependently reversed by addition of sulpiride, a dopamine D2 receptor antagonist, whereas no change was observed by addition of nomifensine (5 X 10(-6) M), a blocker of dopamine uptake. From in vitro experiment using purified TH, OPC-4392 affected neither the enzymatic activity nor the Km value for 6-methyl-5,6,7,8-tetrahydropterin (6MPH4). These results suggest that OPC-4392 impairs in situ DOPA formation by stimulating presynaptic dopamine D2 receptor as a dopamine agonist, and not by directly inhibiting the TH activity.     

Parallel synthesis and dopamine D3/D2 receptor screening of novel {4-[4-(2-methoxyphenyl)piperazin-1-yl]butyl}carboxamides

We have applied a fast and high-yielding method for the parallel amidation of 4-[4-(2-methoxyphenyl)piperazin-1-yl]-butylamine yielding analogs of the partial dopamine receptor agonist BP 897. Using this amino scaffold prepared in solution and polymer-bound carboxylic acid equivalents, we have synthesized a series of high affinity dopamine D(3) receptor ligands. The novel compounds were obtained in good to excellent yield and purity. Biological evaluation included determination of binding affinities at hD(2S) and hD(3) receptor subtypes. From the 22 novel structures presented here, compound 4v showed high affinity (K(i) (hD(3)) 1.6nM) and a 136-fold preference for the D(3) receptor versus that for the D(2) receptor subtype. Our results suggest that this derivatization technique is a useful method to speed up structure-activity relationships studies on dopamine receptor subtype modulators.     

Discovery of a novel class of 1,3-dioxane-2-carboxylic acid derivatives as subtype-selective peroxisome proliferator-activated receptor alpha (PPARalpha) agonists

A new series of 1,3-dioxane-2-carboxylic acid derivatives was synthesized and evaluated for agonist activity at human peroxisome proliferator-activated receptor (PPAR) subtypes. Structure-activity relationship studies led to the identification of 2-methyl-c-5-[4-(5-methyl-2-phenyl-1,3-oxazol-4-yl)butyl]-1,3-dioxane-r-2-carboxylic acid 4b as a potent PPARalpha agonist with high subtype selectivity at human receptor subtypes. This compound exhibited a substantial hypolipidemic effect in type 2 diabetic KK-A(y) mice.     

Identification and SAR around N-{2-[4-(2,3-dihydro-benzo[1,4]dioxin-2-ylmethyl)-[1,4]diazepan-1-yl]-ethyl}-2-phenoxy-nicotinamide, a selective alpha2C adrenergic receptor antagonist

The discovery of the CNS-penetrant and selective alpha(2C) adrenergic receptor antagonist N-{2-[4-(2,3-dihydro-benzo[1,4]dioxin-2-ylmethyl)-[1,4]diazepan-1-yl]-ethyl}-2-phenoxy-nicotinamide, 13 is described. Structure-activity studies demonstrate the structural requirements for binding affinity, functional activity, and selectivity over other alpha(2)-AR subtypes.     

4-Phenyl-4-[1H-imidazol-2-yl]-piperidine derivatives, a novel class of selective delta-opioid agonists

A novel series of 4-phenyl-4-[1H-imidazol-2-yl]-piperidine derivatives has been prepared and their synthesis described herein. In vitro affinities for delta-, mu-, and kappa-opioid receptors, as well as the functional activity in the [(35)S]GTPgammaS assay are reported. The most potent and selective delta-opioid agonist 18a exhibited a K(i) of 18 nM, and was >258-fold and 28-fold selective over mu- and kappa-receptors, respectively; the compound is a full agonist with an EC(50) value of 14 nM.     

(+)-3-[2-(Benzo[b]thiophen-2-yl)-2-oxoethyl]-1-azabicyclo[2.2.2]octane as potent agonists for the alpha7 nicotinic acetylcholine receptor

A series of 3-substituted 1-azabicyclo[2.2.2]octanes was discovered as the alpha7 nicotinic acetylcholine (alpha7) receptor agonists. It was found that (+)-3-[2-(benzo[b]thiophen-2-yl)-2-oxoethyl]-1-azabicyclo[2.2.2]octane (+)-15b has potent agonistic activity for the alpha7 receptor.     

Quinoline- and isoquinoline-sulfonamide derivatives of LCAP as potent CNS multi-receptor-5-HT1A/5-HT2A/5-HT7 and D2/D3/D4-agents: the synthesis and pharmacological evaluation

Two series of arylpiperazinyl-alkyl quinoline-, isoquinoline-, naphthalene-sulfonamides with flexible (13-26) and semi-rigid (33-36) alkylene spacer were synthesized and evaluated for 5-HT(1A), 5-HT(2A), 5-HT(6), 5-HT(7) and selected compounds for D(2), D(3), D(4) receptors. The compounds with a mixed 5-HT and D receptors profile 16 (N-{4-[4-(3-chlorophenyl)-piperazin-1-yl]-butyl}-3-quinolinesulfonamide) and 36 (4-(4-{2-[4-(4-chloro-phenyl)-piperazin-1-yl]-ethyl}-piperidine-1-sulfonyl)-isoquinoline), displaying antagonistic activity at 5-HT(7), 5-HT(2A), D(2) postsynaptic sites, produced antidepressant-like effects in the forced swim test in mice and showed significant anxiolytic activity in the plus-maze test in rats. The lead compound 36, a multi-receptor 5-HT(2A)/5-HT(7)/D(2)/D(3)/D(4) agent, also displayed significant antipsychotic properties in the MK-801-induced hyperlocomotor activity in mice.     

Synthesis and biological evaluation of (2S)- and (2R)-2-(3'-phosphonobicyclo[1.1.1]pentyl)glycines as novel group III selective metabotropic glutamate receptor ligands

The synthesis of (2S)- and (2R)-2-(3'-phosphonobicyclo[1.1.1]pentyl)glycine isomers (10 and 11), characterized by the bioisosteric replacement of the distal carboxylic group of 2-(3'-carboxybicyclo[1.1.1]pent-1-yl)glycine by the phosphonate moiety, was accomplished by a stereoselective Ugi condensation. The two isomers were tested for their activity against an array of metabotropic glutamate receptors, and the S-isomer (10) turned out to be a moderately potent and selective mGluR4 agonist.     

AMPA receptor agonists: Resolution,configurational assignment,and pharmacology of (+)-(S)- and (-)-(R)-2-amino-3-[3-hydroxy-5-(2-pyridyl)-isoxazol-4-yl]-propionic acid (2-Py-AMPA)

We have previously shown that whereas (RS)-2-amino-3-(3-hydroxy-5-phenylisoxazol-4-yl)propionic acid (APPA) shows the characteristics of a partial agonist at (RS)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) receptors, (S)-APPA is a full AMPA receptor agonist and (R)-APPA a weak competitive AMPA receptor antagonist. This observation led us to introduce the new pharmacological concept, functional partial agonism. Recently we have shown that the 2-pyridyl analogue of APPA, (RS)-2-amino-3-[3-hydroxy-5-(2-pyridyl)isoxazol-4-yl]propionic acid (2-Py-AMPA), is a potent and apparently full AMPA receptor agonist, and this compound has now been resolved into (+)- and (-)-2-Py-AMPA (ee ≥ 99.0%) by chiral HPLC using a Chirobiotic T column. The absolute stereochemistry of the enantiomers of APPA has previously been established by X-ray analysis, and on the basis of comparative studies of the circular dichroism spectra of the enantiomers of APPA and 2-Py-AMPA, (+)- and (-)-2-Py-AMPA were assigned the (S)- and (R)-configuration, respectively. In a series of receptor binding studies, neither enantiomer of 2-Py-AMPA showed detectable affinity for kainic acid receptor sites or different sites at the N-methyl-D-aspartic acid (NMDA) receptor complex. (+)-(S)-2-Py-AMPA was an effective inhibitor of [³H]AMPA binding (IC⁵⁰ = 0.19 ± 0.06 μM) and a potent AMPA receptor agonist in the rat cortical wedge preparation (EC₅₀ = 4.5 ± 0.3 μM) comparable with AMPA (IC₅₀ = 0.040 ± 0.01 μM; EC₅₀ = 3.5 ± 0.2 μM), but much more potent than (+)-(S)-APPA (IC₅₀ = 5.5 ± 2.2 μM; EC₅₀ = 230 ± 12 μM). Like (-)-(R)-APPA (IC₅₀ > 100 μM), (-)-(R)-2-Py-AMPA (IC₅₀ > 100 μM) did not significantly affect [³H]AMPA binding, and both compounds were week AMPA receptor antagonists (K_i = 270 ± 50 and 290 ± 20 μM, respectively). Chirality 9:274–280, 1997. © 1997 Wiley-Liss, Inc.     

Resolution, configurational assignment, and enantiopharmacology of 2-amino-3-[3-hydroxy-5-(2-methyl-2H- tetrazol-5-yl)isoxazol-4-yl]propionic acid, a potent GluR3- and GluR4-preferring AMPA receptor agonist

We have previously shown that (RS)-2-amino-3-[3-hydroxy-5-(2-methyl-2H-tetrazol-5-yl)isoxazol -4-yl] propionic acid (2-Me-Tet-AMPA) is a selective agonist at (RS)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) receptors, markedly more potent than AMPA itself, whereas the isomeric compound 1-Me-Tet-AMPA is essentially inactive. We here report the enantiopharmacology of 2-Me-Tet-AMPA in radioligand binding and cortical wedge electrophysiological assay systems, and using cloned AMPA (GluR1-4) and kainic acid (KA) (GluR5, 6, and KA2) receptor subtypes expressed in Xenopus oocytes. 2-Me-Tet-AMPA was resolved using preparative chiral HPLC. Zwitterion (-)-2-Me-Tet-AMPA was assigned the (R)-configuration based on an X-ray crystallographic analysis supported by the elution order of (-)- and (+)-2-Me-Tet-AMPA using four different chiral HPLC columns and by circular dichroism spectra. None of the compounds tested showed detectable affinity for N-methyl-D-aspartic acid (NMDA) receptor sites, and (R)-2-Me-Tet-AMPA was essentially inactive in all of the test systems used. Whereas (S)-2-Me-Tet-AMPA showed low affinity (IC(50) = 11 microM) in the [(3)H]KA binding assay, it was significantly more potent (IC(50) = 0.009 microM) than AMPA (IC(50) = 0.039 microM) in the [(3)H]AMPA binding assay, and in agreement with these findings, (S)-2-Me-Tet-AMPA (EC(50) = 0.11 microM) was markedly more potent than AMPA (EC(50) = 3.5 microM) in the electrophysiological cortical wedge model. In contrast to AMPA, which showed comparable potencies (EC(50) = 1.3-3.5 microM) at receptors formed by the AMPA receptor subunits (GluR1-4) in Xenopus oocytes, more potent effects and a substantially higher degree of subunit selectivity were observed for (S)-2-Me-Tet-AMPA: GluR1o (EC(50) = 0.16 microM), GluR1o/GluR2i (EC(50) = 0.12 microM), GluR3o (EC(50) = 0.014 microM) and GluR4o (EC(50) = 0.009 microM). At the KA-preferring receptors GluR5 and GluR6/KA2, (S)-2-Me-Tet-AMPA showed much weaker agonist effects (EC(50) = 8.7 and 15.3 microM, respectively). It is concluded that (S)-2-Me-Tet-AMPA is a subunit-selective and highly potent AMPA receptor agonist and a potentially useful tool for studies of physiological AMPA receptor subtypes.     

Selective inhibitors of GABA uptake: synthesis and molecular pharmacology of 4-N-methylamino-4,5,6,7-tetrahydrobenzo[d]isoxazol-3-ol analogues

A series of lipophilic diaromatic derivatives of the glia-selective GABA uptake inhibitor (R)-4-amino-4,5,6,7-tetrahydrobenzo[d]isoxazol-3-ol [(R)-exo-THPO, 4] were synthesized via reductive amination of 3-ethoxy-4,5,6,7-tetrahydrobenzo[d]isoxazol-4-one (9) or via N-alkylation of O-alkylatedracemic 4. The effects of the target compounds on GABA uptake mechanisms in vitro were measured using a rat brain synaptosomal preparation or primary cultures of mouse cortical neurons and glia cells (astrocytes), as well as HEK cells transfected with cloned mouse GABA transporter subtypes (GAT1-4). The activity against isoniazid-induced convulsions in mice after subcutaneous administration of the compounds was determined. All of the compounds were potent inhibitors of synaptosomal uptake the most potent compound being (RS)-4-[N-(1,1-diphenylbut-1-en-4-yl)amino]-4,5,6,7-tetrahydrobenzo[d]isoxazol-3-ol (17a, IC50 = 0.14 microM). The majority of the compounds showed a weak preference for glial, as compared to neuronal, GABA uptake. The highest degree of selectivity was 10-fold corresponding to the glia selectivity of (R)-N-methyl-exo-THPO (5). All derivatives showed a preference for the GAT1 transporter, as compared with GAT2-4, with the exception of (RS)-4-[N-[1,1-bis(3-methyl-2-thienyl)but-1-en-4-yl]-N-methylamino]-4,5,6,7-tetrahydrobenzo[d]isoxazol-3-ol (28d), which quite surprisingly turned out to be more potent than GABA at both GAT1 and GAT2 subtypes. The GAT1 activity was shown to reside in (R)-28d whereas (R)-28d and (S)-28d contributed equally to GAT2 activity. This makes (S)-28d a GAT2 selective compound, and (R)-28d equally effective in inhibition of GAT1 and GAT2 mediated GABA transport. All compounds tested were effective as anticonvulsant reflecting that these compounds have blood-brain barrier permeating ability.     

Identification of 2-(4,5,6,7-tetrahydro-1H-pyrrolo[3,2-c]pyridin-3-yl)-ethylamine derivatives as novel GnRH receptor antagonists

A novel series of 2-(4,5,6,7-tetrahydro-1H-pyrrolo[3,2-c]pyridin-3-yl)-ethylamine derivatives were designed and synthesized as GnRH receptor antagonists. SAR studies led to a series of highly active molecules against both the rat and human receptors. Furthermore, one potent compound, 17j, demonstrated dose-dependent LH suppression in castrated rats.     

2-(2-[3-(pyridin-3-yloxy)phenyl]-2H-tetrazol-5-yl) pyridine: a highly potent, orally active, metabotropic glutamate subtype 5 (mGlu5) receptor antagonist

Structure-activity relationship studies on 3-(5-pyridin-2-yl-2H-tetrazol-2-yl)benzonitrile 2 led to the discovery of 2-(2-[3-(pyridin-3-yloxy)phenyl]-2H-tetrazol-5-yl)pyridine (10)-a highly potent and selective mGlu5 receptor antagonist with good brain penetration and in vivo receptor occupancy in rat and cross-species oral bioavailability.