Relationships between the structure of dexoxadrol and etoxadrol analogues and their NMDA receptor affinity

In the mid 1960s the (dioxolan-4-yl)piperidine derivatives dexoxadrol ((S,S)-1a) and etoxadrol ((S,S,S)-2a) were synthesized. Their pharmacological potential as analgesics, anesthetics and local anesthetics was evaluated in animal models and later on in clinical trials with patients. However, severe side effects including psychotomimetic effects, unpleasant dreams and aberrations stopped the clinical evaluation of dexoxadrol and etoxadrol. Both dioxolane derivatives represent NMDA receptor antagonists, which possess high affinity to the phencyclidine binding site within the NMDA receptor associated ion channel. In this review relationships between the structure of acetalic dexoxadrol analogues and homologues and their affinity toward the phencyclidine binding site of the NMDA receptor are summarized. In particular, high affinity is attained with compounds bearing two phenyl residues or one phenyl residue and an alkyl residue with two or three carbon atoms at the acetalic center. At least one oxygen atom of the oxygen heterocycle is necessary. Instead of the entire piperidine ring aminoalkyl substructures are sufficient for strong receptor interactions. Compounds with a primary amino moiety generally display the highest receptor affinity, whereas tertiary amines possess low affinity. Enlargement of the 1,3-dioxolane ring to a 1,3-dioxane ring or elongation of the oxygen heterocycle / amino group distance results in compounds with considerable NMDA receptor affinity.     

Synthesis, absolute configuration, and molecular modeling study of etoxadrol, a potent phencyclidine-like agonist

Etoxadrol (2a), one of the eight possible optical isomers of 2-ethyl-2-phenyl-4-(2-piperidyl)-1,3-dioxolane, was synthesized from (S,S)-1-(2-piperidyl)-1,2-ethanediol, which was obtained from cleavage of dexoxadrol (1a, (S,S)-2,2-diphenyl-4-(2-piperidyl)-1,3-dioxolane). The absolute configuration of etoxadrol hydrochloride, a phencyclidine-like compound biologically, was determined to be 2S, 4S, and 6S at its three chiral centers by single-crystal X-ray analysis. Epietoxadrol (2b), epimeric with etoxadrol at the C-2 center, was also obtained from the synthesis. This much less potent enantiomer has the 2R,4S,6S configuration. The affinity of etoxadrol to the phencyclidine binding site was found to be comparable to that of phencyclidine itself and was 35 times more potent than its epimer, epietoxadrol. Three diastereomeric mixtures were prepared that had low affinity for the phencyclidine site. In studies of the discriminative stimulus properties of these compounds, it was found that only etoxadrol substituted for the phencyclidine stimulus. With use of computer-assisted molecular modeling techniques, a hypothetical phencyclidine binding site model has been developed that, unlike our former hypothesis based on Dreiding models, correctly predicts the higher affinity of etoxadrol and the lesser affinity of epietoxadrol for the phencyclidine site.     

Wash-resistant inhibition of phencyclidine- and haloperidol-sensitive sigma receptor sites in guinea pig brain by putative affinity ligands: determination of selectivity

Several putative affinity ligands, based on the structures of phencyclidine etoxadrol, 5-methyl-10,11-dihydro-5H-dibenzo[a,d] cycloheptene-5,10-imine (MK801) and 1,3-di-(2-methylphenyl)guanidine (DTG) were evaluated in vitro for their ability to produce a wash-resistant inhibition of phencyclidine and sigma receptor sites in homogenates of the brain of the guinea pig. All the phencyclidine-based ligands, including 1-[1-(3-isothiocyanatophenyl)cyclohexyl]piperidine (Metaphit) and (+/-)-N-(2-isothiocyanatoethyl) MK801 [(+/-)-MK801-NCS], produced a wash-resistant inhibition of binding sites for phencyclidine, labelled by [3H]-1-[1-(2-thienyl)cyclohexyl]piperidine ([3H]TCP) and sigma binding sites, labelled by [3H]DTG. The DTG-based ligands, 1-(4-isothiocyanato-2-methylphenyl)-3-(2-methylphenyl)guanidine (DIGIT) and 1-(4-[2-(2-isothiocyanatoethoxy)ethoxy]-2-methyl-phenyl)-3-(2- methylphenyl)guanidine (DIGIE), produced a wash-resistant inhibition of sigma sites, at concentrations as small as 1 microM and also inhibited binding sites for phencyclidine at larger concentrations (100 microM). Both 1-(3-isothiocyanatophenyl)-1-ethyl-4-(2-piperidyl)-1,3-dioxolane (ETOX-NCS) and 1-[1-(3-bromoacetyloxyphenyl)cyclohexyl]-1,2,3,6-tetrahydropyri din e (Bromoacetyl-PCP) were the most potent and selective inhibitors of the binding of [3H]TCP, while DIGIT was the most selective inhibitor of the binding of [3H]DTG. Future studies will examine the selectivity of these agents in vivo after intracerebroventricular administration.     

Characterization of opioid, sigma, and phencyclidine receptors in the neuroblastoma-brain hybrid cell line NCB-20

Opioid, sigma, and phencyclidine (PCP) receptors were characterized in the mouse neuroblastoma--Chinese hamster brain hybrid cell line NCB-20. Quantitative receptor assays under equilibrium binding conditions with highly specific radioligands demonstrated the presence of delta, but not mu or kappa, opioid receptors on NCB-20 cell membranes. NCB-20 cells were shown to possess two distinct sites specific for sigma opioids and PCP derivatives. One site was labeled by (+)-[3H]N-allylnormetazocine [(+)-[3H]SKF-10,047] (Kd = 69 nM; Bmax = 4100 fmol/mg of protein). The rank order of potency of drugs at this site was (+)-3-(3-hydroxy-phenyl)-N-(1-propyl)piperidine [(+)-3-PPP] greater than haloperidol greater than (+)-SKF-10,047 greater than (+/-)-ethylketocyclazocine greater than (+/-)-bremazocine greater than N-[1-(2-thienyl) cyclohexyl]piperidine (TCP) greater than dexoxadrol. This site is similar in its ligand selectivity to the haloperidol-sensitive sigma receptor of rat brain. The other site was labeled by the potent phencyclidine derivative [3H]TCP (Kd = 335 nM; Bmax = 9300 fmol/mg of protein). This density is equivalent to approximately 60,000 sites/cell. The rank order of potency of drugs at this site was TCP greater than (+)-3-PPP greater than PCP greater than dexoxadrol greater than haloperidol greater than cyclazocine greater than levoxadrol greater than (+)-SKF-10,047; mu and delta ligands were inactive. This site is similar to the rat brain PCP receptor. The NCB-20 cell line is the only cultured cell line that has been demonstrated to have PCP receptors.     

Synthesis and anticonvulsant activity of 1-phenylcyclohexylamine analogues

Thirty-eight analogues of 1-phenylcyclohexylamine (PCA), a phencyclidine (PCP) derivative, were examined for their activities in the mouse maximal electroshock (MES) seizure test and in a motor-toxicity assay. In addition, we determined the binding affinities of the compounds for PCP acceptor sites in rat brain membranes labeled with [3H]-1-[1-(2-thienyl)cyclohexyl]piperidine. Many of the analogues were protective against MES seizures (ED50s of 5-41 mg/kg, ip) and all of these compounds caused motor toxicity. The potencies in the motor toxicity and MES seizure tests showed a moderate correlation with the affinities for PCP sites. Several analogues exhibited a greater separation of potencies in the motor toxicity and MES seizure tests than did the parent compound PCA. These were obtained by (i) 3-methylation of the cyclohexyl ring trans to the phenyl ring, (ii) methoxylation at the ortho position on the phenyl ring, and (iii) contraction of the cyclohexane ring to form the corresponding cyclopentane.     

Acylation of sigma receptors by Metaphit, an isothiocyanate derivative of phencyclidine

Pretreatment of guinea pig brain membranes with 1-[1-(3-isothiocyanatophenyl)cyclohexyl]piperidine (Metaphit) caused irreversible and differential inhibition of ligand binding to sigma (sigma) receptors. The concentration of Metaphit required to produce 50% inhibition of binding of [3H]1,3-di-o-tolylguanidine ([3H]DTG), [3H](+)-3-(3-hydroxy-phenyl)-N-(1-propyl)piperidine ([3H](+)-3-PPP), and [3H](+)-N-allylnormetazocine ([3H](+)-SKF 10,047) to sigma receptors was 2, 10 and 50 microM, respectively. This compares to a value of 10 microM for inhibition of [3H]1-[1-(2-thienyl)cyclohexyl]piperidine [( 3H]TCP) binding to phencyclidine (PCP) receptors. While Metaphit was an irreversible, non-competitive inhibitor at PCP receptors, this compound produced irreversible, competitive inhibition at sigma receptors.     

Role of the aromatic group in the inhibition of phencyclidine binding and dopamine uptake by PCP analogs

Thirty-seven arylcyclohexylamines including phencyclidine (PCP) and derivatives, N[1-(2-thienyl)cyclohexyl]piperidine (TCP) and derivatives and N-[1-(2-benzo(b)thiophenyl)cyclohexyl]piperidine (BTCP) were assessed for their ability to inhibit [3H]PCP binding and [3H]dopamine ([3H]DA) synaptosomal uptake. Their pharmacological property (ataxia) was measured by means of the rotarod test. A very good correlation was observed between the inhibition of [3H]PCP binding and the [3H]DA uptake only for arylcyclohexylamines bearing an unmodified phenyl group. Conversely the comparison between the inhibition of [3H]PCP binding and the activity in the rotarod test shows a good correlation with arylcyclohexylamines having any aromatic group (phenyl, substituted phenyl and thienyl rings). This study outlined a new compound (BTCP) without ataxic effect, which is one of the more potent inhibitors of the [3H]DA uptake (IC50 = 8 nM) and which seems very specific since it has a low affinity for [3H]PCP receptors (IC50 = 6 microM). These data show that the aromatic group of the compounds leads to molecules that bind differently to the PCP receptor and to the DA uptake complex. They also suggest that the behavioral properties of arylcyclohexylamines revealed by the rotarod test occur essentially as a result of an interaction with the sites labeled with [3H]PCP and that TCP is more selective than PCP itself in this recognition.     

Quantitative characterization of multiple binding sites for phencyclidine and N-allylnormetazocine in membranes from rat and guinea pig brain.

Quantitative ligand binding studies have been used to characterize binding sites for N-allylnormetazocine ((+)SKF10,047) (SKF), 1-(1-phenylcyclohexyl) piperidine (PCP), N-[1-(2-thienyl)cyclohexyl]piperidine (TCP) and haloperidol in membranes from the brain of rat and guinea pig under conditions which permitted simultaneous analysis of the binding of both PCP and SKF. Using four labelled ligands (SKF, TCP, PCP and haloperidol), each displaced by the corresponding four unlabelled ligands, four classes of binding sites were observed in membranes from the brain of the rat, corresponding to sigma (sigma), two classes of PCP sites (PCP1, PCP2) and dopamine (D2) sites. The sigma site was suppressed by 50 nM haloperidol, while the PCP1 and PCP2 sites were not. These results were confirmed by studies employing a self- and cross-displacement design and dose-response surfaces for SKF and TCP, with and without blockade by haloperidol of the sigma site. Using mathematical modelling, employing the program LIGAND, it was possible to reject simpler models involving a common "PCP/sigma" site or a model involving only two classes of sites (sigma and PCP). Similar methods were used to identify two classes of sigma binding sites and two classes of PCP binding sites, in membranes prepared from the brain of the guinea pig. The relative potencies of 18 ligands for displacement of (+)[3H]SKF10,047 and [3H]TCP were compared: there were significant qualitative and quantitative differences in the "sigma" binding sites in the brain of rat and guinea pig, while the PCP binding sites were very similar in the two species.     

Synthesis, stereochemistry, and biological activity of the 1-(1-phenyl-2-methylcyclohexyl)piperidines and the 1-(1-phenyl-4-methylcyclohexyl)piperidines. Absolute configuration of the potent trans-(-)-1-(1-phenyl-2-methylcyclohexyl)piperidine

The (-)- and (+)-isomers of the cis- and trans-Ph/Me 1-(1-phenyl-2-methylcyclohexyl)piperidines have been synthesized and the achiral cis- and trans-Ph/Me 1-(1-phenyl-4-methylcyclohexyl)piperidines were prepared, and their in vitro [displacement of [3H]TCP (1-[1-(2-thienylcyclohexyl)]piperidine) from the PCP (1-(1-phenylcyclohexyl)piperidine) binding site] and in vivo (rotarod assay) activities determined. The 1-(1-phenyl-2-methylcyclohexyl)piperidine isomers were resolved by classical crystallization procedures, through the diastereomeric salts obtained with d- and l-10-camphorsulfonic acid. The relative stereochemistry of the cis- and trans-Ph/Me 1-(1-phenyl-2-methylcyclohexyl)piperidines and the achiral cis- and trans-Ph/Me 1-(1-phenyl-4-methylcyclohexyl)piperidines was established by using 13C and 1H NMR. Both (-)-trans-1-(1-phenyl-2-methylcyclohexyl)piperidine ((-)-2) and (+)-trans-1-(1-phenyl-2-methylcyclohexyl)piperidine ((+)-2) were examined by single-crystal X-ray analysis, and the absolute configuration of (-)-2 was determined to be 1S,2R. The (-)-2 was found to be about five times more potent than PCP in vitro and twice as potent in vivo. It is the most potent of all of the simple methyl-substituted cyclohexyl PCP isomers and is among the most potent PCP-like compounds which have been synthesized. It was nine times more potent in vitro and four times more potent in vivo than (+)-2. The racemic cis-1-(1-phenyl-2-methylcyclohexyl)piperidine (3), and its enantiomers ((+)-3 and (-)-3), were essentially inactive in vitro and in vivo. The cis-Ph/Me 1-(1-phenyl-4-methylcyclohexyl)piperidine (18) was more potent than trans-Ph/Me 1-(1-phenyl-4-methylcyclohexyl)piperidine (17), but considerably less potent than (-)-2. The enantioselectivity observed at the PCP binding site for (-)-2 could indicate that this site can discriminate between enantiotopic edges of the achiral PCP (choosing the pro-1-S edge), as does the mu-opioid receptor in the prodine series of opioids. Benzimidoyl or benzoyl group replacement of the phenyl ring in the 1-(1-phenyl-2-methylcyclohexyl)piperidine series gave compounds which showed little in vitro and in vivo activity.     

强效镇痛剂研究——Ⅱ.3-甲基芬太尼类衍生物的合成及镇痛活性

本文报道了N-[1-(β-苯乙基)-3-甲基-4-哌啶基]-N-丙酰苯胺(7209)和N-[1-(β-羟基-β-苯乙基)-3-甲基-4-哌啶基]-N-丙酰苯胺(7302)等一系列3-甲基芬太尼类衍生物的合成及镇痛活性。绝大部分该类衍生物均具有典型的吗啡样镇痛活性,是一类结构较简单、易于合成、镇痛作用极强的麻醉镇痛剂。化合物7302的ED₅₀为0.0022mg/kg(ip,小鼠,热板法),比芬太尼强28倍,竟达吗啡的6318倍,为我们至今合成该类衍生物中作用最强者。     

Phencyclidine/SKF-10,047 binding sites: evaluation of function

Results of correlation analyses comparing rank-order affinities with rank-order potencies of (+)SKF-10,047, phencyclidine (PCP), and several PCP analogs support the involvement of [3H]-1-[1-(2-thienyl)cyclohexyl]piperidine binding sites (TCP sites) in mediating both the discriminative stimulus properties of PCP and production of 180 degrees perseveration in a 4-arm radial maze. For the same group of drugs, no significant relationship was found to exist between affinities at haloperidol-sensitive (+)[3H]SKF-10,047 binding sites (H-S-SKF sites) and potencies. Also, H-S-SKF sites were found to lack pharmacological selectivity and to be localized in the microsomal fraction of cells. It is concluded that TCP sites may represent receptors which mediate effects not only of PCP, but also of (+)SKF-10,047. In addition, the possibility that H-S-SKF sites may represent a type of membrane-bound enzyme is discussed.     

苯环利定衍生物和苯环利定／ 类药物对电场刺激引起大鼠肠...

Using the model of perfused mesenteric arteries of rat, we studied the effect of phencyclidine (PCP), N-[1-(2-thienyl)cyclohexyl] piperidine (TCP), N,N-dimethylphenylcyclohexylamine (PCDA), N-(iso-propyl)-1-phenylcyclohexylamine (PCIPA), (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801), (+),(-)-N-allylnormetazocine (SKF 10 047), dextrorphan, and levorphanol on vasoconstrictor response induced by electrical field stimulation. PCP, TCP, PCDA, PCIPA, MK-801, levorphanol, and (-)-SKF 10 047 were found to increase the vasoconstrictor response in dose-dependent manner. The dose-effect curves of these compounds were similar to the curve of PCP. Although dextrorphan, an antagonist for PCP receptors, did not affect the vasoconstrictor response, it could non-competitively antagonize PCP's action. These studies suggest that some PCP analogs and PCP/sigma ligands may enhance the vasoconstrictor response induced by electrical field stimulation via action on PCP receptors.     

A comparison of the reinforcing efficacy of PCP, the PCP derivatives TCP and BTCP, and cocaine using a progressive ratio schedule in the rat

This study was designed to compare the reinforcing efficacy of PCP (phencyclidine:phenylcyclohexyl-piperidine) and the PCP-derivatives BTCP (N-[1-(2-benzo(b)thiophenyl) cyclohexyl]piperidine) and TCP (N-[1-(2-thienyl)cyclohexyl]-piperidine) to that of cocaine, using a progressive ratio schedule of reinforcement (PR). On the PR schedule the number of responses required to obtain an i.v. infusion of drug was escalated with each injection until a breaking point was reached when the animal stopped responding. Since BTCP has an affinity for the DA uptake site comparable to that of cocaine, it was hypothesized that BTCP and cocaine would show similar patterns of self-administration and comparable breaking points. In contrast, the high affinity of TCP and PCP for the NMDA-ion channel complex suggested that these two compounds would also support comparable self-administration behaviors. Rats were trained to self-administer i.v. cocaine during daily 5h sessions under a fixed-ratio-1 (FR1) schedule. Once consistent lever-pressing behavior was established, BTCP, PCP or TCP was substituted for cocaine. Under the FRI schedule, BTCP elicited a regular pattern of lever pressing, unlike PCP and TCP. However, under the PR schedule BTCP elicited breaking points comparable to those produced by equivalent doses of cocaine, whereas TCP and PCP produced considerably lower breaking points. These results suggest that BTCP has comparable rewarding properties to that of cocaine, and that like those of cocaine they are most probably mediated through a site of action at the DA transporter. In contrast, the relatively weak reinforcing efficacy of PCP and TCP would correlate better with their primary site of action on the PCP binding site within the NMDA-ion channel complex.     

Synthesis and analgesic effects of new pyrrole derivatives of phencyclidine in mice

Phencyclidine (1-(1-phenylcyclohexyl)piperidine, CAS 956-90-1, PCP, I) and many of its analogues have shown some pharmacological effects. In this study, new pyrrole derivatives of I (1-(1-phenylcyclohexyl)pyrrole, II and 1-[1-(4-methylphenyl)(cyclohexyl)]pyrrole, III) and their intermediates were synthesized and the acute and chronic pains were examined on mice using tail immersion (as a model of acute thermal pain) and formalin (as a model of acute and chronic chemical pain) tests and the results were compared with the PCP and control groups. The results indicated that III generated higher analgesic effects in the tail immersion test compared to the PCP and control (dimethyl sulfoxide, DMSO) groups, demonstrating a marked and significant increase in tail immersion latency, but this effect was not observed for II in the dose of 1 mg/kg. The formalin test showed that III was effective in acute chemical pain (phase I, 0-5 min after injection), but was not effective for II at the same dosage compared to the PCP and control groups. Also chronic pain will be significantly attenuated by III but II was not effective as compared to the other groups. It is concluded that substitution of the aromatic pyrrole ring instead of piperidine in the PCP molecule will not be effective alone in tail immersion and formalin tests but the addition of a methyl group (with high electron donating and dipole moments) on the phenyl group plus substitution of the aromatic pyrrole ring can be effective in acute and chronic pain compared to the PCP and control groups.     

The pharmacokinetics of [3H]1-[1-(2-thienyl)cyclohexyl]piperidine (TCP) in Sprague-Dawley rats

Using adult male Sprague-Dawley rats, we examined the blood protein binding and pharmacokinetics of the potent phencyclidine (PCP) receptor ligand 1-[1-(2-thienyl)cyclohexyl]piperidine (TCP). The average percentage of unbound [3H]TCP in rat serum was 42 +/- 6% and the [3H]TCP blood to plasma ratio was 0.98 +/- 0.03 (mean +/- SD, n = 5 in both studies). For the pharmacokinetic studies, [3H]TCP and 1 mg/kg unlabeled TCP were administered as an iv bolus dose. The average [3H]TCP elimination half-life was 2.1 hr. In contrast, total radioactivity in the plasma had a much longer half-life, suggesting much slower metabolite elimination. The average distribution volumes were 27 +/- 17, 15.6 +/- 6.2, and 5.6 +/- 3.0 liters/kg for V beta, Vss, and Vc, respectively. Total body and renal clearance values were 132 +/- 45 and 1.1 +/- 0.4 ml/min/kg, respectively. When TCP pharmacokinetic parameters were compared to PCP pharmacokinetic data in rats from a previous study, a strikingly similar pharmacokinetic profile was found. These data indicated that TCP and PCP are equivalent, from a pharmacokinetic point of view, and that the higher pharmacological potency of TCP over PCP is probably due to receptor-mediated differences.     

Oral self-administration of phencyclidine analogs by rhesus monkeys: Conditioned taste and visual reinforcers

Three monkeys self-administered orally-delivered phencyclidine, 1-(1-phencyclohexyl) piperidine (PCP), N-ethyl-1-phencyclohexylamine (PCE), and 1-[1-(2-thienyl)cyclohexyl]piperidine (TCP) over a wide range of concentrations (0.0156, 0.0312, 0.0625, 0.125, 0.25, and 0.5 mg/ml). Water was also available under a concurrent fixed-ratio (FR) 16 schedule. Drug deliveries were substantially higher than concurrent water deliveries at all concentrations, indicating that the three compounds functioned as effective reinforcers. Maximum liquid deliveries occurred at concentrations of 0.0625 (PCP and TCP) and 0.125 mg/ml (PCE). TCP was much shorter-acting (10–15 min) than PCP (4–6 h) based on observations of severe ataxia at high concentrations. To investigate the conditioned reinforcing effects of taste, a quinine solution (0.088 mg/ml) was substituted for PCP (0.25 mg/ml) in five monkeys. Four monkeys responded for quinine in excess of water for a range of seven to over 30 sessions, while one monkey (M-R) did not show any substantial responding for quinine. With the same five monkeys (treatment order mixed), the effect of visual stimuli was tested by substituting water for PCP while retaining the visual stimuli indicating drug availability. Four monkeys showed increased responding on the side signaling drug for only 0–4 sessions, while one monkey (M-R) showed persistent responding for water on the side with drug stimuli for 29 sessions. These results indicated that taste functioned as an effective conditioned reinforcer, while visual stimuli appeared to be less effective in the oral drug self-administration paradigm.     

(1,3-Dialkyl-5-amino-1H-pyrazol-4-yl)arylmethanones. A series of novel central nervous system depressants

A series of novel (1,3-dialkyl-5-amino-1H-pyrazol-4-yl)arylmethanones was synthesized. Pharmacological evaluation of these compounds demonstrated central nervous system depressant activity, potential anticonvulsant properties, and a low order of acute toxicity. In addition, selected compounds showed potential antipsychotic effects. This report focuses on the synthesis and structure-activity relationships of these compounds. (5-Amino-1-ethyl-3-methyl-1H-pyrazol-4-yl)(2-chlorophenyl) methanone (21) was the most active compound against pentylenetetrazole-induced convulsions. (5-Amino-1,3-dimethyl-1H-pyrazol-4-yl)(3-chlorophenyl)methanone (4) also has a favorable anticonvulsant depression ratio. (5-Amino-1,3-dimethyl-1H-pyrazol-4-yl)(3-trifluoromethylphenyl)methan one (8), (5-amino-1,3-dimethyl-1H-pyrazol-4-yl)(3-thienyl)methanone (13), and (5-amino-3-ethyl-1-methyl-1H-pyrazol-4-yl)phenylmethanone (14) are very potent depressants. (5-Amino-1,3-dimethyl-1H-pyrazol-4-yl)(2-thienyl)methanone (12) possessed marked central depressant activity without anticonvulsant activity and without impairment of motor functioning. (5-Amino-1,3-dimethyl-1H-pyrazol-4-yl) (2-fluorophenyl)methanone (2) has a behavioral profile suggestive of antipsychotic activity and gave a positive Ames test result.     

The rat brain phencyclidine (PCP) receptor. A putative K+ channel

Receptor binding studies were carried out to test whether the rat brain phencyclidine (PCP) receptor is part of a K+ channel. [3H]PCP, and two analogs, [3H]TCP and m-amino[3H]PCP, labeled a single receptor on rat brain synaptic membranes. Each compound bound to a similar number of sites (Bmax = 2.7 pmol bound/mg protein); the apparent dissociation constants for these compounds (KD less than 0.3 microM) decreased with increasing temperature. The following observations indicate that the PCP receptor is part of a K+ channel: (1) aminopyridines (AP) and tetraalkylammonium ions blocked [3H]PCP binding; their respective orders of potency, 4-AP = 3,4-diAP much greater than 3-AP, and tetrabutylammonium (TBA) greater than tetraethylammonium much greater than tetramethylammonium, paralleled their abilities to block K+ channels, (2) the order of potency of PCP and its analogs for binding to the PCP receptor, TCP greater than PCE greater than m-amino-PCP greater than PCP greater than PCPY greater than m-nitro-PCP, paralleled their rank order for blocking brain K+ channels, and (3) the stereospecific displacement of [3H]PCP binding by the isomers of the "sigma" ligands, (+)N-allyl-normetazocine (NANM) greater than (-)NANM, and (-)cyclazocine greater than (+)cyclazocine, and of the dioxolanes, dexoxadrol much greater than levoxadrol, paralleled their abilities to block brain K+ channels. Reciprocal plot and Schild plot analyses indicated that TBA, (+)NANM and dexoxadrol were competitive inhibitors at the PCP receptor, whereas 4-AP had an allosteric interaction.     

The psychotomimetic drug phencyclidine labels two high affinity binding sites in guinea pig brain: evidence for N-methyl-D-aspartate-coupled and dopamine reuptake carrier-associated phencyclidine binding sites

Numerous studies have now demonstrated that a binding site for the psychotomimetic drug phencyclidine (PCP) exists within the receptor channel complex for the excitatory amino acid neurotransmitter glutamate, specifically the glutamate receptor selectively activated by N-methyl-D-aspartate (NMDA). Several lines of evidence support the hypothesis that all PCP receptors in rat brain are associated with the NMDA receptor complex. In the present study, we reexamine this hypothesis. We report that the PCP analog [3H]1-[1-(2-thienyl)cyclohexyl]piperidine [( 3H]TCP) labels two high affinity binding sites in membranes prepared from guinea pig brain site 1 (Kd = 14.1 nM, Bmax = 631 fmol/mg of protein) and site 2 (Kd = 46.5 nM, Bmax = 829 fmol/mg of protein). (+)-5-Methyl-10 11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate bound to site 1 with high affinity (Kl = 3.2 nM) and to site 2 with low affinity (Kl = 5208 nM). The order of potency of drugs for inhibiting [3H]TCP binding to site 1 correlated with their ED50 values for inhibition of NMDA-mediated responses reported in the literature, whereas the order of potency of drugs for inhibiting [3H]TCP binding to site 2 correlated with their ED50 values for inhibition of [3H]dopamine reuptake reported in the literature. Kinetic experiments demonstrated that glutamate, 2-amino-7-phosphonoheptanoic acid, and Mg2+ modulated [3H]TCP binding to site 1 but not site 2. Preincubation of guinea pig striatal membranes with varying concentrations of the high affinity dopamine reuptake inhibitors N-[1-(2-benzo(b)thiophenyl)cyclohexyl]piperidine and 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-[3- phenylpropyl]piperazine caused a wash-resistant inhibition of [3H]TCP binding to site 2 but not site 1. Taken collectively, these data demonstrate the existence of a high affinity PCP binding site associated with the dopamine reuptake carrier and raise the possibility that the therapeutic and psychotomimetic effects of PCP in humans are separable and mediated via different binding sites.     

Desipramine and the phencyclidine derivative BTCP differently inhibit [3H]TCP binding to high- and low-affinity sites.

The effects of N-[1-(2-benzo(b)thiophenyl)cyclohexyl]piperidine (BTCP) and desipramine on [3H]N-[1-(2-thienyl)cyclohexyl]piperidine ([3H]TCP) binding were investigated in vivo and in vitro. In the cerebrum, both drugs were competitive inhibitors of high-affinity [3H]TCP binding. Conversely, in the cerebellum, they were non-competitive inhibitors of low-affinity [3H]TCP binding. These results imply that the different [3H]TCP binding sites have distinct pharmacological properties, and show that, although chemically related to TCP, BTCP has an effect similar to that of desipramine.