Synthesis and structure-activity relationships of naphthamides as dopamine D3 receptor ligands

A series of naphthamides were synthesized, and the affinities of these compounds were determined for dopamine D2 and D3 receptors using radioligand binding techniques. The naphthamide compounds that were prepared include N-(1-alkylpiperidin-4-yl)-4-bromo-1-methoxy-2-naphthamides (1-6), (S)-N-(1-alkylpyrrolidin-3-yl)-4-bromo-1-methoxy-2-naphthamides (7-12), (R)-N-(1-alkylpyrrolidin-3-yl)-4-bromo-1-methoxy-2-naphthamides (13-18), (S)-N-(1-alkyl-2-pyrrolidinylmethyl)-4-bromo-1-methoxy-2-naphthamides (19-25), (R)-N-(1-alkyl-2-pyrrolidinylmethyl)-4-bromo-1-methoxy-2-naphthamides (26-31), and N-(9-alkyl-9-azabicyclo[3.3.1]nonan-3beta-yl)-4-bromo-1-methoxy-2-naphthamides (32, 33). The results of in vitro radioligand binding studies indicated that the majority of the naphthamide analogues bound with high affinity at both the D2 and D3 dopamine receptor subtypes and most of the compounds demonstrated some selectivity for the dopamine D3 dopamine receptor subtype. These results demonstrated that both the structure of the central amine moiety (piperidine, pyrrolidine, and 9-azabicyclo[3.3.1]nonane) ring and the N-(alkyl) substitution on the amine significantly effects the binding affinity at D2 and D3 dopamine receptors. The bulkiness of the N-(1-alkyl) substituent was found to (a) have no effect on pharmacologic selectivity, (b) increase the affinity at D3 receptors, or (c) decrease the affinity at D2 receptors. The most potent analogue in this series was (S)-N-(1-cycloheptylpyrrolidin-3-yl)-4-bromo-1-methoxy-2-naphthamide (10), which had equilibrium dissociation (K(i)) values of 1.8 and 0.2 nM for D2 and D3 receptors, respectively. The most selective analogue was (R)-N-(1-cycloheptyl-2-pyrrolidinylmethyl)-4-bromo-1-methoxy-2-naphthamide (30), which had K(i) values of 62.8 and 2.4 nM for D2 and D3 receptors, respectively. Radioligand binding results for sigma receptors indicated that the structure of the amine moiety and the N-(1-alkyl) substitutions also significantly influence the affinity and selectivity of these compounds at the sigma1 and sigma2 sigma receptor subtypes. The two naphthamides containing a 9-azabicyclo[3.3.1]nonan-3beta-yl central ring were found to be selective for sigma2 receptors.     

(8-Naphthalen-1-ylmethyl-4-oxo-1-phenyl-1,3,8-triaza-spiro[4. 5]dec-3-yl)-acetic acid methyl ester (NNC 63-0532) is a novel potent nociceptin receptor agonist

Spiroxatrine was identified as a moderately potent (K:(i)=118 nM) but non-selective agonist at the human nociceptin/orphanin FQ receptor, ORL1. This compound was subject to chemical modification and one of the resulting compounds, (8-naphthalen-1-ylmethyl-4-oxo-1-phenyl-1,3,8-triaza-s piro[4. 5]dec-3-yl)-acetic acid methyl ester (NNC 63-0532) was shown to have high affinity for ORL1 (K:(i)=7.3 nM). NNC 63-0532 showed only moderate affinity for the following receptors (K:(i) values in parentheses): mu-opioid (140 nM), kappa-opioid (405 nM), dopamine D(2S) (209 nM), dopamine D(3) (133 nM) and dopamine D(4.4) (107 nM) out of 75 different receptors, ion-channels and transporters. In functional assays, NNC 63-0532 was shown to be an agonist at ORL1 (EC(50)=305 nM), a much weaker agonist at the mu-opioid receptor (EC(50)>10 microM) and an antagonist or weak partial agonist at dopamine D(2S) (IC(50)=2830 nM). Thus, NNC 63-0532 is a novel non-peptide agonist with approximately 12 fold selectivity for ORL1 and may be useful for exploring the physiological roles of this receptor owing to its brain-penetrating properties.     

Synthesis and binding profile of constrained analogues of N-[4-(4-arylpiperazin-1-yl)butyl]-3-methoxybenzamides, a class of potent dopamine D3 receptor ligands

We recently reported on a series of N-[4-(4-arylpiperazin-1-yl)butyl]-3-methoxybenzamides, endowed with high affinity for dopamine D(3) receptors, but lacking of selectivity over D(4), D(2), 5-HT(1A), and alpha(1)-receptors. To improve the D(3)-receptor affinity and selectivity, without causing a considerable increasing in the lipophilicity, the flexible butyl linker was replaced by a more conformationally constrained cyclohexyl linker. The new cis- and trans-N-[4-(4-aryl-1-piperazinyl)cyclohexyl]-3-methoxybenzamides (Aryl= 2,3-di-Cl-Ph, 2-CH(3)O-Ph, 4-Cl-Ph, 2,3-di-CH(3)-Ph) were tested in-vitro for their binding affinity for D(3), D(4), D(2), 5-HT(1A), and alpha(1)-receptors. The trans- derivatives were found to be more potent at D(3) receptor than the corresponding cis- isomers, but less potent than the opened counterparts. This reflected negatively on the selectivity over the other studied receptors. Derivative trans-N-{4-[4-(2,3-dichlorophenyl)-1-piperazinyl]cyclohexyl}-3-methoxybenzamide (trans-7) showed high D(3)-receptor affinity (K(i)=0.18 nM) and a relevant selectivity over D(4), D(2), 5-HT(1A), and alpha(1)-receptors (>200-fold). This compound was characterized as a full agonist at D(3) receptor when tested in the Eu-GTP binding assay.     

Sigma2 (sigma2) receptors as a target for cocaine action in the rat striatum

Studies from our laboratory have shown that agonists at sigma1 and sigma2 receptors inhibit N-methyl-D-aspartate (NMDA)-stimulated dopamine release from motor and limbic areas of rat brain. In the current study, we examined the effects of cocaine on N-methyl-D-aspartate (NMDA)-stimulated [3H]dopamine release in rat striatal slices. Cocaine inhibited N-methyl-D-aspartate-stimulated [3H]dopamine release in a concentration-dependent manner with a Ki of approximately 10 microM, under conditions in which the dopamine transporter (DAT) was blocked by 10 microM nomifensine. The inhibition seen by cocaine was reversed by the selective sigma2 antagonist 1'-[4-[1-(4-fluorophenyl)-1H-indol-3-yl]-1-butyl]-spiro[isobenzofuran-1(3H), 4'piperidine] (Lu28-179). Inhibition of release by cocaine and (+)pentazocine, under conditions in which sigma1 receptors were blocked, was also reversed by the conventional PKC inhibitor 3-[1-[3-(dimethylamino)propyl-1H-indole-3-yl]-1-H-pyrpole-2-5'-dione. These results suggest that cocaine or other agonists, acting through the sigma2 receptor, require an intact conventional PKC (cPKC), most likely PKCalpha or PKCgamma in order to inhibit dopamine release.     

Synthesis, monoamine transporter binding, properties, and functional monoamine uptake activity of 3beta-[4-methylphenyl and 4-chlorophenyl]-2 beta-[5-(substituted phenyl)thiazol-2-yl]tropanes

Synthetic methods were developed for the synthesis of the 3beta-(4-substituted phenyl)-2 beta-[5-(substituted phenyl)thiazol-2-yl]tropanes (4a-s). The compounds were evaluated for their monoamine transporter binding and monoamine uptake inhibition properties using both rat brain tissue and cloned transporter assays. In general, the compounds showed higher dopamine transporter (DAT) affinity relative to the serotonin and norepinephrine transporters (SERT and NET, respectively) and greater [3H]dopamine uptake inhibition potency relative to [3H]serotonin and [3H]norepinephrine uptake inhibition. Several compounds were DAT selective relative to the SERT and NET in the monoamine transporter binding assays. The most potent and selective analog in the functional monoamine uptake inhibition test was 3beta-(4-methylphenyl-2 beta-[5-(3-nitrophenyl)thiazol-2-yl]tropane (4p).     

N(alpha)-imidazolylalkyl and pyridylalkyl derivatives of histaprodifen: synthesis and in vitro evaluation of highly potent histamine H(1)-receptor agonists

A novel series of N(alpha)()-imidazolylalkyl and pyridylalkyl derivatives of histaprodifen (6, 2-[2-(3,3-diphenylpropyl)imidazol-4-yl]ethanamine) was synthesized and evaluated as histamine H(1)-receptor agonists. The title compounds displayed partial agonism at contractile H(1)-receptors of guinea pig ileum and were at least equipotent with histamine. Agonist effects of the new derivatives were susceptible to blockade by the H(1)-receptor antagonist mepyramine (2-100 nM). In the imidazole series, suprahistaprodifen (51, [2-[2-(3,3-diphenylpropyl)-1H-imidazol-4-yl]ethyl]-[2-(1H-imidazol-4-yl)ethyl]amine, N(alpha)-2-[(1H-imidazol-4-yl)ethyl]histaprodifen) showed the highest H(1)-receptor agonist potency ever reported in the literature (pEC(50) 8.26, efficacy E(max) 96%). Elongation of the alkyl spacer from ethyl to butyl decreased activity from 3630% (ethyl, 51) to 163% (butyl, 53) of histamine potency. The exchange of the terminal imidazole nucleus for a pyridine ring resulted in compounds with comparably high potency. A decrease in agonist potency and efficacy was observed when the attachment of the alkyl spacer was consecutively changed from the ortho to the meta and the para position, respectively, of the pyridine ring. The pyridine series that contained a butyl chain possessed the highest potency and affinity. N(alpha)-[4-(2-pyridyl)butyl]histaprodifen (56) emerged as a strong partial agonist, being almost equipotent with 51 (pEC(50) 8.16, E(max) 89%). Compounds 51 and 56 also showed potent partial agonism at contractile H(1) receptors in guinea pig aorta and potently activated H(1)-receptor-mediated endothelium-dependent relaxation in the rat aorta. Compounds 51-65 displayed low to moderate affinity at H(2), H(3), and M(3) receptors in functional models of guinea pig. Collectively, N(alpha)-imidazolylalkyl- and N(alpha)-pyridylalkyl-substituted histaprodifens represent a novel class of potent H(1)-receptor agonists. These compounds may be useful to define the (patho)physiological role of the H(1)-receptor and refine molecular models of H(1)-receptor activation.     

Benz[f]isoquinoline analogues as high-affinity sigma ligands.

This paper describes the synthesis of some conformationally restricted 4-phenylpiperidine analogues and their affinities for the guinea pig cerebellum sigma recognition site ([3H]-DTG) and the rat striatum dopamine D2 receptor ([3H]-(-)-sulpiride) in order to develop potent selective sigma ligands as tools in the investigation of this site in psychosis. It was found that both hexa- and octahydrobenz[f]isoquinolines with lipophilic N-substituents had high affinities for the sigma site. Notably, trans-3-cyclohexyl-1,2,3,4,4a,5,6,10b-octahydrobenz[f]isoquinoline (26) had an affinity of 0.25 nM making it the highest affinity sigma ligand reported to date. Moreover, it is at least 10,000-fold selective over the D2 receptor and could prove to be a valuable tool in the study of sigma sites. Other analogues such as 1H-indeno[2,1-c]pyridines and 1H-benzo[3,4]cyclohepta[1,2-c]pyridines also displayed high sigma site affinity.     

Involvement of mast cells, sensory afferents and sympathetic mechanisms in paw oedema induced by adenosine A(1) and A(2B/3) receptor agonists

The novel benzopyranopyrrole, S33084 ((3aR,9bS)-N[4-(8-cyano-1,3a,4, 9b-tetrahydro-3H-benzopyrano[3,4-c]pyrrole-2-yl)-butyl] (4-phenyl)benzamide)), and the aminotetralin derivative, GR218,231 (2(R,S)-(di-n-propylamino)-6-(4-methoxyphenylsulfonylmethyl)-1,2,3 , 4-tetrahydro naphthalene), displayed high affinity at cloned, rat dopamine D(3) receptors (pK(i)s of 8.72 and 8.67, respectively), as well as dopamine D(3) receptors in rat olfactory tubercle (8.62 and 8.94, respectively). In contrast, they showed low affinities at striatal dopamine D(2) receptors (6.82 and 6.64, respectively). Unlike S33084 and GR218,231, the arylpiperazine, L741,626 (4-(4-chlorophenyl)-1-(1H-indol-3-ylmethyl)piperidin-4-ol), showed lower affinity for cloned (6.46) and native (6.92) dopamine D(3) receptors than for striatal dopamine D(2) receptors (7.52). S33084, GR218,231 and L741,626 should prove useful tools for exploration of the functional roles of dopamine D(3) vs. dopamine D(2) receptors.     

Effects of RPR 118723, a novel antagonist at the glycine site of the NMDA receptor, in vitro

RPR 118723 ((8-chloro-5-methyl-2,3-dioxo-1,4-dihydro-5H-indeno[1, 2-b]pyrazin-5-yl) acetic acid) was previously reported to exhibit potent affinity for the glycine site of the N-methyl-D-aspartate (NMDA) receptor-channel complex in the nanomolar range (K(i)=3.1+/-0. 8 nM). We now report on the effects of RPR 118723 in two functional tests reflecting the interaction between the glycine site and the NMDA receptor. First, RPR 118723 potently inhibited [3H]N-[1-(2-thienyl)cyclohexyl]-3,4-piperidine ([3H]TCP) binding in the presence of NMDA (IC(50)=3.5+/-0.4 nM). Second, RPR 118723 antagonized the NMDA-induced increase in [3H]dopamine release in mouse striatal slices (IC(50)=8.0+/-1.1 nM). In both experimental models, an excess of glycine reversed the effect of RPR 118723. These results show that RPR 118723 interferes functionally in the nanomolar range with the glycine site coupled to the NMDA receptor in vitro. The blockade of the glycine site with RPR 118723 may be useful for the therapy of the disorders linked to excessive NMDA stimulation.     

Novel sigma receptor ligands: synthesis and biological profile

The aim of the present study was to investigate the biological profile of new substituted 1-phenyl-2-cyclopropylmethylamines. High affinity for both sigma subtypes was achieved when 4-phenylpiperidin-4-ol (4a-e) and 4-benzylpiperidine moieties were present (5a-e). (1R,2S/1S,2R)-2-[4-Hydroxy-4-phenylpiperidin-1-yl)methyl]-1-(4-methylphenyl)cyclopropanecarboxylate (4b) showed high affinity for the sigma1 sites (Ki = 1.5 nM) and the most favorable sigma1/sigma2 selectivity (Ki(sigma2)/Ki(sigma1) = 33.9). Binding affinity studies showed that 4b binding on N-methyl-d-aspartate (NMDA), dopaminergic (D1, D2, D3), muscarinic, histaminergic H1, adrenergic (alpha1, alpha2), serotoninergic (5-HT2A, 5-HT2C, 5-HT3, 5-HT4, 5-HT6), DA (DAT), and 5-HT (SERT) transporters was not significant. Interestingly, sigma ligands differently induced the expression of tissue transglutaminase (TG-2) in primary astroglial cell cultures. We suggest that 4b may act as a sigma1/sigma2 agonist and that the sigma ligands may modulate TG-2 differently.     

Synthesis of chiral 1-[omega-(4-chlorophenoxy)alkyl]-4-methylpiperidines and their biological evaluation at sigma1, sigma2, and sterol delta8-delta7 isomerase sites

Sumitomo's patented sigma ligand 1-[3-(4-chlorophenoxy)propyl]-4-methylpiperidine (15), which has been claimed as agent for CNS disorders and neuropathies, and its lower homologue 12 were prepared along with related chiral (4-chlorophenoxy)alkylpiperidines. They were tested at sigma1, sigma2, and sterol Delta8-Delta7 isomerase (SI) sites by in vitro radioligand binding assays, to evaluate the influence of a chiral center in the alkyl chain on the selective sigma(1) binding relative to other sigma family sites. Generally high sigma1-site affinities were found, so that the chirality introduced by a methyl substitution resulted in slight differences. Nevertheless, the shorter oxyethylenic chain was beneficial to increase sigma1 selectivity. However, the (-)-(S)-4-methyl-1-[2-(4-chlorophenoxy)-1-methylethyl]piperidine ((-)-(S)-17) reached the highest sigma1 affinity (K(i) = 0.34 nM) and the best selectivity relative to the sigma2 site (547-fold). Compound (-)-(S)-17 displayed also a moderate selectivity (11-fold) relative to the SI site.     

Lu 28-179 labels a sigma(2)-site in rat and human brain

1'-[4-[1-(4-Fluorophenyl)-1H-indol-3-yl]-1-butyl]spiro[isobenzofuran-1(3H),4'-piperidine] (Lu 28-179) or Siramesine is a sigma-ligand with high specificity for sigma(2)-sites, has been tritiated to directly label these sites in brain. [(3)H]Lu 28-179 bound in a saturable manner to homogenates prepared from rat brain or human cortices with high affinity (K(d)=2.2 and 1.1 nM, respectively) and moderate capacity (B(max)=50+/-12 and 26+/-3 fmol mg tissue(-1), respectively). The rank order of affinity for [(3)H]Lu 28-179 binding to homogenates from human and rat brain was: Lu 28-179>ifenprodil=haloperidol>1,3-di(2-tolyl)-guanidine (DTG)>(-)pentazocinez.Gt;(+)pentazocine. Using in vitro receptor autoradiography to rat brain sections [(3)H]Lu 28-179 binding was shown to be most predominant in the cerebral cortex, piriform cortex, hippocampal formation (CA1-CA3 and dentate gyrus), superior colliculus, molecular layer of the cerebellar cortex and locus coeruleus. Overall, these data are consistent with [(3)H]Lu 28-179 labelling a sigma(2)-like binding site.     

Synthesis and in vitro Evaluation of Novel Indole-Based Sigma Receptors Ligands

To investigate the molecular features involved in sigma (σ) receptors binding, a series of compounds based on indole scaffolds were synthesized and their chemical structures were confirmed by (1) H-NMR, IR, and elemental analysis. Their affinity toward σ(1) and σ(2) receptor subtypes was evaluated. 1-{[4-(2-phenylethyl)piperazin-1-yl]methyl}-3-methyl-1H-indole 3b had a high affinity to σ(1) receptors, while three compounds, 1-{3-[4-(substitutedphenyl)piperazin-1-yl]propyl}-1H-indole derivatives 4a-c had shown high affinity and selectivity for σ(2) receptors. Cytotoxicity of the compounds was demonstrated on cancer cell lines from liver (HUH7), breast (MCF7), and colon (HCT-116) cancer cell lines. Compound 1c (3-{[4-(3,4-dichlorobenzyl)piperazin-1-yl]methyl}-1H-indole) showed significant cell growth inhibitory activity on the selected cancer cell lines.     

3H]N-[4-(3,4-dihydro-6,7-dimethoxyisoquinolin-2(1H)-yl)butyl]-2-methoxy-5-methylbenzamide: a novel sigma-2 receptor probe

N-[4-(3,4-dihydro-6,7-dimethoxyisoquinolin-2(1H)-yl)butyl]-2-methoxy-5-methyl-benzamide (RHM-1) and N-[2-(3,4-dihydro-6,7-dimethoxyisoquinolin-2(1H)-yl)ethyl]-2-methoxy-5-methylbenzamide (RHM-2), two conformationally flexible benzamide analogues, were radiolabeled with tritium (specific activity=80 Ci/mmol) and the binding of [3H]RHM-1 and [3H]RHM-2 to sigma-2 (sigma2) receptors was evaluated in vitro. [3H]RHM-1 was found to have a higher affinity for sigma2 receptors compared to [3H]RHM-2 and [3H]1,3-di-o-tolylguanidine ([3H]DTG). [3H]RHM-1 had a dissociation constant (Kd) of 0.66+/-0.12 nM in rat liver membrane homogenates, which was 30-fold higher than that of [3H]RHM-2 (Kd=19.48+/-0.51 nM). The lower affinity of [3H]RHM-2 can be attributed to its faster K(off) rate since both radioligands have similar K(on) rates. Competitive binding assays were also conducted using a panel of compounds with known affinity for sigma2 receptors. The pharmacologic profile of [3H]RHM-1 was in agreement with that of [3H]DTG. The results of this study indicate that [3H]RHM-1 is a useful ligand for studying sigma2 receptors in vitro.     

4-(tetralin-1-yl)- and 4-(naphthalen-1-yl)alkyl derivatives of 1-cyclohexylpiperazine as sigma receptor ligands with agonist sigma2 activity

Several 1-cyclohexylpiperazine derivatives related to sigma(2) receptor ligand 1-cyclohexyl-4-[3-(5-methoxy-1,2,3,4-tetrahydronaphthalen-1-yl)propyl]piperazine (33, K(i) = 0.34 nM) were synthesized and tested in radioligand binding assays, to attempt a structure-affinity relationship study. Intermediate alkyl chain length and methoxyl group position on the tetralin nucleus were varied. A few naphthalene analogues were also prepared. High affinities were found in sigma(2) receptor binding for almost all compounds, some of which displayed K(i) values in subnanomolar range, but low sigma(2)/sigma(1) selectivities were found. The highest sigma(2) affinities were displayed by compounds with an intermediate alkyl chain of three (32 and 43) or five methylenes (39 and 46). Quite high sigma(1) receptor affinity was found for compounds with a four-methylene chain; 36 (K(i) = 0.036 nM) and 45 (K(i) = 0.22 nM) displaying good sigma(1)/sigma(2) selectivity (406- and 139-fold, respectively). Moreover, homologues of compound 33 displayed also satisfactory selectivities over dopamine D(2)-like, serotonin 5-HT(3), and adrenergic alpha(1) receptors. These compounds and a few others were tested in the inhibition of the electrically evoked contractions in guinea pig bladder and were demonstrated to be full sigma(2) agonists. The activity values correlated well to the affinity scale (EC(50) in microM range). 33 and related compounds are proposed as a class of potential antineoplastic and PET diagnosis agents.     

Inhibition by sigma receptor ligand, MS-377, of N-methyl-D-aspartate-induced currents in dopamine neurons of the rat ventral tegmental area

RATIONALE: MS-377 [( R)-(+)-1-(4-chlorophenyl)-3-[4-(2-methoxyethyl) piperazin-1-yl]methyl-2-pyrrolidinone L-tartrate] is a novel anti-psychotic drug candidate with high affinity for sigma receptors but devoid of binding affinity for PCP binding site of NMDA receptor/ion channel complex. OBJECTIVES: The effects of MS-377 on NMDA receptor and/or its ion channel complex were examined to elucidate the antipsychotic properties of MS-377. METHODS: We examined the effect of MS-377 on NMDA ( N-methyl- D-aspartate)-induced current in acutely dissociated dopamine neurons of rat ventral tegmental area (VTA) using patch clamp whole cell recording. RESULTS: MS-377 applied in a bath inhibited the peak current evoked by NMDA applied via the U-tube method for 2 s in a concentration-dependent manner. Other sigma receptor ligands, BD-1063 (1-[2-(3,4-dichlorophenyl)ethyl]-4-methylpiperazine), NE-100 ( N, N-dipropyl-2-[4-methoxy-3-(2-phenylenoxy)-phenyl]-ethylamine monohydrochloride) and haloperidol also inhibited NMDA-induced current in a concentration-dependent manner. Interestingly, concomitant application of MS-377 with BD-1063, NE-100 or haloperidol at concentrations that had no effects on NMDA-induced current, potentiated the MS-377-induced inhibition. CONCLUSIONS: The results suggest that MS-377, as well as other sigma receptor ligands, indirectly acts on the sigma receptor to inhibit glutaminergic transmission mediated by NMDA receptor/ion channel complex in VTA dopamine neurons, thereby inhibiting dopamine release in target VTA areas.     

Binding of [3H]U-101958 to sigma1 receptor-like sites in human cerebellum and neuroblastoma cells.

1-Benzyl-4-[N-(3-isopropoxy-2-pyridinyl)-N-methyl]-amino-piperidine ([3H]U-101958), a dopamine D4 receptor ligand, was found to bind to a large sigma1 receptor-like component in human cerebellum and SK-N-MC neuroblastoma cells with high affinity (2-4 nM Kd). By contrast, binding to dopamine D4 receptors represented 10% or less of the sigma1 receptor-like site. Considering that U-101958 has been characterized as either a dopamine D4 receptor agonist or antagonist, depending on the system under study, the observation that U-101958 also binds to sigma1 receptor-like sites is important for accurate interpretation of the pharmacological actions of this compound. [3H]U-101958 may be a useful radioligand for sigma1 rather than dopamine D4 receptor sites.     

Novel spiropiperidines as highly potent and subtype selective sigma-receptor ligands. Part 1.

A series of spiro[[2]benzopyran-1,4'-piperidines] and spiro[[2]benzofuran-1,4'-piperidines] of general structure 10 is prepared, and the affinity for sigma(1)- and sigma(2)-receptors is investigated by means of radioligand binding assays. The synthesis of the spiropiperidines 14a and 23 proceeds from bromine/lithium exchange of the bromoacetals 11 and 21, addition to piperidin-4-one 12a, and subsequent cyclization. Systematic variations of the substituent R at the nitrogen atom, the group X in position 3, and the ring size of the oxygen heterocycle are performed. The sigma(1)- and sigma(2)-receptor affinities are determined with guinea pig brain and rat liver membrane preparations using [(3)H]-labeled (+)-pentazocine and ditolylguanidine, respectively. Test results show that a benzyl residue at the piperidine nitrogen atom and a methoxy group in position 3 are advantageous for high sigma(1)-receptor affinity. In this series the 1'-benzyl-3-methoxy-3,4-dihydrospiro[[2]benzopyran-1,4'-piperidine] (14a) and the 1'-benzyl-3-methoxy-3H-spiro[[2]benzofuran-1,4'-piperidine] (23) are among the most potent sigma(1)-ligands interacting in the low nanomolar range with sigma(1)-receptors (14a, K(i) = 1.29 nM; 23, K(i) = 1.14 nM). Variation of the nitrogen substituent R from benzyl to H, alkyl, phenyl, or omega-phenylalkyl and the group X from methoxy to hydroxy, carbonyl, or alkyloxy led to reduced sigma(1)-receptor affinity. In addition to their high sigma(1)-receptor affinity, the spiropiperidines 14a and 23 display excellent selectivity toward sigma(2)-receptors (sigma(1)/sigma(2) = 2708 and 1130) and several other receptor and reuptake systems. Introduction of a polar hydroxy group in position 3 and elongation of the distance between the piperidine nitrogen atom and the phenyl moiety result in ligands with considerable sigma(2)-receptor affinity and therefore diminished sigma(1)/sigma(2)-receptor selectivity. The hemiacetalic 1'-(3-phenylpropyl)-3,4-dihydrospiro[[2]benzopyran-1,4'-piperidin]-3-ol (15e) represents the most active sigma(2)-receptor ligand in this series with a K(i) value of 83.1 nM.     

A structure-affinity relationship study on derivatives of N-[2-[4-(4-Chlorophenyl)piperazin-1-yl]ethyl]-3-methoxybenzamide, a high-affinity and selective D(4) receptor ligand

N-[2-[4-(4-Chlorophenyl)piperazin-1-yl]ethyl]-3-methoxybenzamide (1), a high-affinity and selective dopamine D(4) receptor ligand, was chosen as a lead, and structural modifications were done on its amide bond and on its alkyl chain linking the benzamide moiety to the piperazine ring and by preparing some semirigid analogues. The binding profile at dopamine D(4) and dopamine D(2), serotonin 5-HT(1A), and adrenergic alpha(1) receptors of 16 new compounds was determined. From the results emerged that the modification of the amide bond and the elongation of the intermediate alkyl chain caused a decrease in dopamine D(4) receptor affinity. All prepared semirigid analogues displayed D(4) receptor affinity values in the same range of the opened counterparts.     

Synthesis, alpha-adrenoceptors affinity and alpha 1-adrenoceptor antagonistic properties of some 1,4-substituted piperazine derivatives

A series of different 1,4-substituted piperazine derivatives (1-11) was synthesized. It comprised 1-(substituted-phenoxyalkyl)-4-(2-methoxyphenyl)piperazine derivatives (1-5); 1,4-bis(substituted-phenoxyethyl)piperazine derivatives (6-8) and 1-(substituted-phenoxy)-3-(substituted-phenoxyalkylpiperazin-1-yl)propan-2-ol derivatives (9-11). All compounds were evaluated for affinity toward alpha 1- and alpha 2-receptors by radioligand binding assays on rat cerebral cortex using [3H]prazosin and [3H]clonidine as specific radioligand, respectively. Furthermore alpha 1-antagonistic properties were checked for most promising compounds (1-5 and 10) by means of inhibition of phenylephrine induced contraction in isolated rat aorta. Antagonistic potency stayed in agreement with radioligand binding results. The most active compounds (1-5) displaced [3H]prazosin from cortical binding sites in low nanomolar range (Ki = 2.1-13.1 nM). Compound 10 showed slightly lower affinity for alpha 1-adrenoceptor (Ki = 781 nM). Compounds 2-5 displayed the strongest antagonistic activity with pA2 values ranging from 8.441 to 8.807. Compound 1 gave a pA2 value of 7.868, while compound 10 showed the weakest antagonistic potency, giving a pA2 value of 6.374. 1-[3-(2-Chloro-6-methylphenoxy)propyl]-4-(2-methoxyphenyl)piperazine hydrochloride (5) showed the best alpha 1- affinity properties with a Ki(alpha 1) value of 2.1 nM and it was 61.05 fold more selective toward alpha 1 than alpha 2-receptors. The best properties showed 1-[3-(2,6-dimethylphenoxy)propyl]-4-(2-methoxyphenyl)piperazine hydrochloride (4) with a Ki(alpha 1) value of 2.4 nM, a 142.13 fold better selectivity to alpha 1 - over alpha 2-adrenoceptors and the best antagonistic potency (pA2 = 8.807). It is worth to emphasized that all most promising compounds possessed an 1-(o-methoxyphenyl)piperazine moiety which probably plays an important role in the affinity to alpha-adrenoceptors.