Pyridobenzoxazepine and pyridobenzothiazepine derivatives as potential central nervous system agents: synthesis and neurochemical study

8-Chloro-5-(4-phenethylpiperazin-1--yl)pyrido[2,3-b][1,5]benzoxazepine

As part of an anti-psychotic drug discovery program, we report the crystal structure of the title compound, C(24)H(23)ClN(4)O. The mol-ecule has a tricyclic framework with a characteristic buckled V-shaped pyridobenzoxazepine unit, with the central seven-membered heterocycle in a boat configuration. The piperazine ring displays a chair conformation with the 2-phenyl-ethyl substituent assuming an equatorial orientation. There are two crystallographically independent, but virtually identical, mol-ecules in the asymmetric unit.

A new strategy toward fused-pyridine heterocyclic scaffolds: Bischler-Napieralski-type cyclization, followed by sulfoxide extrusion reaction

Method development was completed for a new strategy to obtain fused-pyridine heterocyclic scaffolds. The synthetic route entails a Bischler-Napieralski-type reaction as the key step, followed by a sulfoxide extrusion reaction. The reactions of 3-amino-2-arylthiopyridines or 3-amino-4-arylthiopyridines and carboxylic acids promoted by a Lewis acid such as SnCl4 yielded novel tricyclic pyridobenzothiazepines, which could be readily converted to their corresponding oxidized products via a sequence of sulfur oxidations and eventually to benzonaphthyridines via a sulfoxide extrusion. The synthetic strategy provides an efficient way to access libraries of novel structurally diversified heterocyclic compounds with potential pharmaceutical or biological activities.

Olanzapine and JL13 induce cross-tolerance to the clozapine discriminative stimulus in rats

We have previously shown that chronic treatment with clozapine induces tolerance to the clozapine discriminative stimulus in rats. The studies reported here extended this work to assess whether chronic treatment with the clozapine-like antipsychotics olanzapine and 5-(4-methylpiperazin-1-yl)-8-chloro-pyrido[2,3-b][1,5] benzoxazepine fumarate (JL13) induced cross-tolerance to clozapine. Two groups of rats were trained to discriminate clozapine (5 mg/kg, intraperitoneal). Training was suspended and the rats were treated with either olanzapine or JL13 at high doses (5 and 20 mg/kg, respectively). These doses were administered twice daily. The clozapine generalization curve was computed three times - before chronic drug treatment, after 10 days of chronic treatment, and after 16 drug-free days. Both olanzapine and JL13 induced cross-tolerance to the clozapine stimulus, shown by significant 3.4 and 3.9 fold parallel shifts to the right in the clozapine generalization curves. Cross-tolerance was lost spontaneously during the drug-free days after treatment as clozapine sensitivity returned to baseline. We interpret these findings as indicative of the development of pharmacodynamic cross-tolerance to clozapine. Possible neuroadaptive mechanisms involved in such cross-tolerance are discussed. The paradigm outlined here allows refinement of antipsychotic drug discrimination assays to identify common chronic effects of such drugs.

Synthesis and in vitro binding studies of substituted piperidine naphthamides. Part I: Influence of the substitution on the basic nitrogen and the position of the amide on the affinity for D2L, D4.2, and 5-HT2A receptors

A series of 1- and 2-naphthamides has been prepared and tested for in vitro binding to D(2L), D(4.2), and 5-HT(2A) receptors. Different compounds display selectivity for D(4.2) and 5-HT(2A) receptors versus D(2L) receptors. N-(1-Arylalkyl-piperidin-4-yl) carboxamides have higher affinities than the corresponding N-(4-arylalkylamino-piperidin-1-yl) carboxamide analogues. A benzyl moiety in position 1 of the piperidine in the 2-naphthamide series (2) appears to be the best choice for a favorable interaction with D(4.2) and 5-HT(2A) receptors. Increasing the linker length between the phenyl ring and the basic nitrogen led to a decreased affinity for these receptors. In the 1-naphthamide series, the most potent D(4.2) ligand (7) possesses a phenylpropyl moiety while its affinity for 5-HT(2A) receptors is strongly reduced. All compounds with significant affinity for D(4.2) and 5-HT(2A) receptors were antagonists.

JL 13, an atypical antipsychotic: a preclinical review

The extensive pharmacological evaluation of JL 13 as an atypical antipsychotic drug has revealed a close similarity to clozapine, however with some major advantages. JL 13 was characterized as a weak D(2) antagonist, both in vitro and in vivo, with a strong affinity for the D(4) and the 5-HT(2A) receptors. It has no affinity for the 5-HT(2C) receptor. In vivo microdialysis experiments in rat showed that JL 13, like clozapine, preferentially increased extracellular dopamine concentrations in the prefrontal cortex compared to nucleus accumbens or striatum. Behavioral studies showed that JL 13, like clozapine, has the profile of an atypical antipsychotic. Thus, JL 13 did not antagonize apomorphine-induced stereotypy nor did it produce catalepsy, but it antagonized apomorphine-induced climbing in rodents. It was inactive against d-amphetamine-induced stereotypy but antagonized d-amphetamine-induced hyperactivity in the mouse. Likewise, in the paw test, it was more effective in prolonging hindlimb retraction time than prolonging forelimb retraction time. Like other antipsychotic drugs, JL 13 reversed the apomorphine- and amphetamine-induced disruption of prepulse inhibition. In a complex temporal regulation schedule in the dog, JL 13 showed a high resemblance with clozapine without inducing sialorrhea, palpebral ptosis or any significant motor side effects. In rats and squirrel monkeys JL 13 induced a high degree of generalization (70%) to clozapine. Regarding behavioral toxicology, JL 13 did not produce dystonia or Parkinsonian symptoms in haloperidol-sensitized monkeys. After acute administration, again like clozapine, JL 13 induced only a transient increase in circulating prolactin. Last but not the least, regarding a possible hematological toxicity, unlike clozapine, JL 13 did not present sensitivity to peroxidase-induced oxidation. Moreover, its electrooxidation potential was close to that of loxapine and far from that of clozapine. Taking all these preclinical data into account, it appears that JL 13 is a promising atypical antipsychotic drug.

Synthesis of a carbon-14 analogue of 8-chloro-11-(4-methyl-1-piperazinyl)-11-[14C]-dibenz[b,f][1,4]oxazepine

8-Chloro-11-(4-methyl-1-piperazinyl)-dibenz[b,f][1,4]oxazepine labelled with carbon-14 in 11-position was prepared from 2-hydroxy benzonitrile-[cyano-14C].

Minimal effects of JL 13, a pyridobenzoxazepine derivative with an antipsychotic potential, on circulating prolactin levels in male rats

Antipsychotic therapy is frequently associated with several side effects such as hyperprolactinemia. The influence of a putative antipsychotic JL 13 on prolactin release was assessed after intraperitoneal injection in gentled male rats in comparison with clozapine and haloperidol. A total of 30 or 150 min after administration, whole blood was collected for preparing serum samples. Prolactin was quantified by radioimmunoassay method. At 30 min, JL 13 like clozapine, increased prolactin concentration only at the higher dose (30 mg/kg) while haloperidol at both tested doses induced a dramatic increase of prolactin concentration. At 150 min after injection, only haloperidol (0.3 mg/kg) significantly increased serum prolactin level. This minimal effect on prolactinemia reinforces the similarity of clozapine and JL 13 regarding the atypical antipsychotic profile.

Distribution of the methylpiperazinopyridobenzoxazepine derivative JL13, a potential antipsychotic, in rat brain

The brain uptake and distribution of the potential antipsychotic 5-(4-methylpiperazin-1-yl)-8-chloro-pyrido[2,3][1,5]benzoxazepine fumarate (JL13) was examined in rats after neuropharmacologically active doses. Plasma and brain concentrations of the compound were measured by reversed-phase HPLC with UV detection (210 nm). Clozapine was used as an internal standard. After an intraperitoneal dose of 10 mg kg(-1), the compound attained mean maximum plasma concentrations within 5 min of dosing, then declined with a mean elimination half-life of approximately 1 h. It rapidly crossed the blood-brain barrier and equilibrated with plasma, achieving mean maximum concentrations and area under the curve approximately 20-times those in plasma, with slight regional differences. Disappearance from whole brain almost paralleled its disappearance from plasma. There was a linear relationship between JL13 concentrations in plasma and brain regions, and in all tissues the concentrations of the compound increased almost linearly with the dose over the range of 5-20 mg kg(-1). It thus appears that JL13 brain pharmacokinetics parallels that in plasma, and that plasma concentrations accurately predict brain concentrations in rats.

Effects of JL 3, a putative antidepressant, on rat noradrenergic and serotonergic systems

Using in vitro electrophysiological procedures, we confirm the inhibitory effect of 10-(4-methylpiperazin-1-yl)pyrido[4,3-b][1, 4]benzothiazepine (JL 3), on dorsal raphe serotonergic (IC(50)=14 microM) and noradrenergic neurons (IC(50)=4.5 microM). The effect on dorsal raphe neurons was reduced by N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinyl- cyclohexanecarboxamide (WAY-100635), suggesting the importance of 5-HT(1A) receptor stimulation. Yohimbine, and ritanserin, to a lesser extent, blocked the inhibitory effect of JL 3 on locus coeruleus neurons indicating that alpha(2)-adrenoceptors and 5-HT(2A) receptors may be implicated in the effects. Because of its negligible alpha(2)-adrenoceptor affinity, the effect of JL 3 on locus coeruleus neurons, would have to be indirect. JL 3 may interfere with the norepinephrine transporter site (IC(50)=0.34 microM). JL 3 tended to reinforce the hypertensive effect of norepinephrine, while it strongly inhibited the hypertensive effect of tyramine, further indicating an interaction at the norepinephrine transporter site level.

Oxidation sensitivity may be a useful tool for the detection of the hematotoxic potential of newly developed molecules: application to antipsychotic drugs

Some antipsychotic agents have been found to produce agranulocytosis and aplastic anemia. The oxidation phenomena and/or the formation of free radicals has been suggested to be causally related to various hematological disorders, e.g., agranulocytosis. Using five experimental conditions, we tested the oxidative potential of compounds with and without a history of hematological side effects, e.g., agranulocytosis and aplastic anemia. A statistical analysis was undertaken for each experimental condition and a multivariate analysis combining all results was performed. Two peroxidase-induced free radical models did not successfully discriminate between drugs with and without a history of causing hematologic problems (<70%). The lipid peroxidation system provided even less satisfactory discrimination, with only 56.25% correct classification. However, an 87.5% correct classification was obtained when using the oxidation potentials of these drugs determined at pH 4.7 and at pH 7.4. A multivariate analysis taking into account the five variables provided 87.5% success in classification. The two clusters were better discriminated in terms of a "distance coefficient." In a second analysis, the putative antipsychotic pyridobenzodiazepine analogues (JL5, JL8, JL18, and JL25) were classified in the cluster of toxic compounds, while the oxa- and thiazepine analogues (JL2, JL3, and JL13) were classified as nontoxic compounds. On the other hand, a few metabolites of clozapine and fluperlapine were classified in the toxic compound group. The procedure described herein is, to our knowledge, the first which classifies molecules of different structures as well as different pharmacological profiles according to their hematotoxic potential. Such a procedure could be used to predict drug-induced hematological side effects.

JL 13, a potential successor to clozapine, is less sensitive to oxidative phenomena

The oxidation behaviour of JL 13, a promising antipsychotic, was investigated in comparison with clozapine and loxapine, by measuring their direct "radical scavenging" abilities and their efficacies in inhibiting the lipid peroxidation. In the lipid peroxidation system, the reactivity of these compounds with free radicals produced by gamma-irradiation of linoleic acid may be presented as follows: JL 13 = loxapine < clozapine. In two enzymatic systems (HRP/GSH and HRP/H2O2/ GSH) which generate the thiyl free radicals, clozapine produces a strong enhancement of the thiyl-radical EPR signal intensity while JL 13 and loxapine exhibit no or minimal effect on this signal. The redox potential values for the three derivatives confirm the spectro-photometric and EPR results. Following this study, we show that JL 13, although presenting a preclinical clozapine-like profile, appears less sensitive to oxidation than clozapine.

Dibenzoazepine analogues: the electrophysiological properties of JL3, a potential atypical antidepressant

JL3, 10-(4-methylpiperazin-1-yl)pyrido[4,3-b][1,4]benzothiazepine, has potent antidepressant-like activity in Porsolt's test in mice. Therefore, its influence on the electrical activity of central monoaminergic neurons was investigated in rats anaesthetized with chloral hydrate. JL3 induced a marked decrease of the firing rate of dorsal raphe serotonergic neurons (ID50 = 3.87 +/- 0.57 mg kg-1) and of locus coeruleus noradrenergic neurons (ID50 = 2.63 +/- 0.35 mg kg-1). The drug did not modify the electrical activity of A10 dopaminergic neurons. JL3 does not block amine uptake but it has affinity for 5-HT1A and 5-HT2 receptors. It is speculated that serotonergic mechanisms could play a role in the electrophysiological effects of JL3.

Antipsychotics and neuropeptides: the atypical profile of CI-943 and its relationship to neurotensin

CI-943 is a new drug candidate with antipsychotic-like activity in a variety of behavioural tests in rodents and primates, but without any affinity for brain dopamine receptors. CI-943 does not cause dystonia in monkeys, a predictive symptom of extrapyramidal side effects (EPS). Its mechanism of action remains unclear. Neurotensin (NT) concentration in nucleus accumbens and caudate is increased by CI-943; this may be associated with its antipsychotic effect. Indeed various observations suggest that the clinical action of antipsychotic drugs may at least be partially mediated by some neuropeptides. Various actions of neurotensin are reviewed. The hypothesis on the role of neurotensin represents a new strategy in the development of pharmacological tools for the treatment of schizophrenia.