Synthesis and monoamine transporter affinity of 2beta-carbomethoxy-3beta-(4'-p-substituted phenyl)-piperidine analogs of cocaine.

A series of novel piperidine based analogs of cocaine was synthesized and evaluated in vitro against the three monoamine transporters to develop new potential selective SERT radiotracers. Modification of the phenyl substitution with five-membered heterocyclic groups resulted in a wide affinity and selectivity scale. Radiolabeling and mouse in vivo study was performed on the piperidine analog of ZIENT, which crossed the blood-brain barrier but failed to selectively accumulate in the regions of the brain rich in SERT.

Synthesis and monoamine transporter affinity of new 2beta-carbomethoxy-3beta-[aryl or heteroaryl]phenyltropanes.

A series of 16 new 2beta-carbomethoxy-3beta-[aryl or heteroaryl]phenyltropane derivatives was synthesized and evaluated for binding to monoamine transporters. Most of the compounds exhibited nanomolar affinity for the serotonin transporter (SERT). Four compounds presented a particularly attractive pharmacological profile, with very high SERT affinity (K(i) 0.15-0.5 nM) and selectivity versus the dopamine transporter of 25- to 77-fold.

Synthesis and dopamine receptor binding of sulfur-containing aporphines.

We investigated acid-catalyzed rearrangement of thebaine 14 and its N-propyl analog 15 with methanesulfonic acid in the presence of the nucleophiles methanethiol and hydrogen sulfide. R(-)-2-methylthioapocodeine 16, R(-)-2-methylthioapomorphine 18, and their N-n-propyl analogs 17, 19 were obtained by rearrangement in the presence of methanethiol. However, with hydrogen sulfide, rearrangement of thebaine 14 and its N-n-propyl analog 15 produced sulfide-linked bis-aporphines 21-24 instead of expected R(-)-2-mercaptoapocodeines 12, 13 and R(-)-2-mercaptoapomorphines 10, 11. R(-)-2-Methylthio-N-n-propylnorapomorphine 19 had higher affinity (Ki = 3.7 nM) at D2 receptors in rat forebrain tissue than other novel 2-substituted sulfur-containing aporphines (Ki > or = 50 nM). Behavioral testing of the novel agents in rat indicated moderate locomotor arousal after systemic injection, and none after intragastric administration, indicating poor oral bioavailability.

Synthesis and monoamine transporter affinity of new 2beta-carbomethoxy-3beta-[4-(substituted thiophenyl)]phenyltropanes: discovery of a selective SERT antagonist with picomolar potency.

Preparation of cocaine analogues has been aimed largely at development of stable compounds with high affinity and selectivity for the dopamine transporter (DAT). We now report the synthesis and monoamine transporter affinity of 10 new 2beta-carbomethoxy-3beta-[4-(substituted thiophenyl)]phenyltropanes. Among these, compound 4b exhibited very high affinity for the serotonin transporter (SERT: K(i)=17 pM) and good selectivity over dopamine (DAT: 710-fold) and norepinephrine transporters (NET: 11,100-fold).

Synthesis and amine transporter affinities of novel phenyltropane derivatives as potential positron emission tomography (PET) imaging agents.

A series of novel fluoroalkyl-containing tropane derivatives (6-8, 10-14, 17, and 18) were synthesized from cocaine. Novel compounds were evaluated for affinity and selectivity in competitive radioligand binding assays selective for cerebral serotonin (5-HT), dopamine (DA), and norepinephrine (NE) transporters (SERT, DAT, and NET). The nortropane-fluoroalkyl esters (7, 10, 11) were most potent for SERT (K(i): 0.18, 0.24, and 0.30 nM, respectively). Tosylate esters 17 and 18, synthesized as precursors for [(18)F]-labeled, Positron Emission Tomography (PET) imaging agents, also showed high affinity for DAT.

Synthesis and neuropharmacological evaluation of R(-)-N-alkyl-11-hydroxynoraporphines and their esters.

We synthesized several N-substituted-11-hydroxynoraporphines and their esters of varying chain length, evaluated their binding affinity at dopamine (DA) receptor sites in rat caudate-putamen membranes, and quantified their effects on motor activity in normal adult male rats. The 11-hydroxyaporphines showed similar neuropharmacological properties to the corresponding 10,11-catecholaporphines. At moderate doses, their esters proved to have more prolonged behavioral actions and superior oral bioavailability.

Synthesis and monoamine transporter affinity of 3'-analogs of 2-beta-carbomethoxy-3-beta-(4'-iodophenyl)tropane (beta-CIT).

The 3'-iodo positional isomer of 2-beta-carbomethoxy-3-beta-(4'-iodophenyl)tropane (beta-CIT) and other 3'-substituted analogs were synthesized and evaluated for binding to monoamine transporters in rat forebrain and membranes of cell lines selectively expressing human transporter genes. All 3'-substituted compounds displayed affinity for both serotonin (SERT) and dopamine (DAT), but much less for norepinephrine transporters (NET), with selectivity for rat (r) or human (h) SERT over NET, but only 3'-iodo-substituted phenyltropanes showed selectivity for SERT versus DAT. The 3'-iodo, N-methyl analog of beta-CIT (7) displayed 29-fold selectivity and high affinity for hSERT (K(i) =9.6 nM) over hDAT (K(i) =279 nM), and its nor-congener (8) showed even higher hSERT potency (K(i) =1.2 nM) and selectivity over DAT (415-fold).

Synthesis and affinity of a possible byproduct of electrophilic radiolabeling of [123I]IBZM.

The iodobenzamide neuroleptic analogue (S)-N-(1-ethylpyrrolidin-2-ylmethyl)-2-hydroxy-5-iodo-6-methoxybenzamide (5-IBZM) was synthesized stereospecifically and its pharmacological properties were compared with the 3-iodo isomer (IBZM) used for imaging D(2) receptors in vivo. The isomer 5-IBZM had 100-fold lower affinity than IBZM and migrated with similar retention time as the byproduct formed during electrophilic iodination of BZM.

Receptor affinities of dopamine D1 receptor-selective novel phenylbenzazepines.

We prepared a series of 18 novel substituted phenylbenzazepine congeners of the dopamine D1/D5 receptor partial-agonist SKF-83959 (R,S-3-methyl-6-chloro-7,8-dihydroxy-1-[3'-methylphenyl]-2,3,4,5-tetrahydro-1H-benzazepine) and characterized their potency and selectivity in assays of dopamine, 5-HT and adrenoceptors in rat brain tissue or membranes of genetically transfected cells. The R-enantiomer of SKF-83959 (MCL-202) and three other novel racemic 1-phenyl-7,8-dihydroxybenzazepines (MCL-204, -203, and -207) showed very high dopamine D5 receptor affinity; MCL-209 displayed the greatest dopamine D5 receptor affinity. These five potent novel ligands also had >100-fold selectivity for dopamine D1 over dopamine D2, D3, serotonin 5-HT-2A receptors and alpha2-adrenoceptors. They require further functional testing to characterize their intrinsic activity, and for potential stimulant-antagonist actions, as observed with SKF-83959 and MCL-202.

Long-term effects of olanzapine, risperidone, and quetiapine on ionotropic glutamate receptor types: implications for antipsychotic drug treatment.

Levels of ionotropic glutamate (Glu) N-methyl-d-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and kainic acid (KA) receptors in rat forebrain regions were compared by quantitative in vitro receptor autoradiography after continuous treatment for 28 days with the atypical antipsychotics olanzapine, risperidone, and quetiapine, or vehicle controls. All three treatments significantly decreased NMDA binding in caudate-putamen (CPu; by 30, 34, and 26%, respectively) but increased AMPA receptor levels in same region (by 22, 30, and 28%). Olanzapine and risperidone, but not quetiapine, also reduced NMDA receptor labeling in hippocampal CA1 (21 and 19%) and CA3 (23 and 22%) regions. KA receptors were unaltered by any treatment in the brain regions examined. These findings suggest that the antipsychotic effects of olanzapine and risperidone may be mediated in part by NMDA receptors in hippocampus, and perhaps AMPA receptors in CPu. The findings also support the hypothesis that down-regulation of NMDA receptors by atypical antipsychotic agents in CPu contributes to their low risk of extra-pyramidal side effects. Inability of olanzapine, risperidone, and quetiapine to alter KA receptors suggests their minimal role in mediating the central nervous system actions of these drugs.

Synthesis, receptor potency, and selectivity of halogenated diphenylpiperidines as serotonin 5-HT2A ligands for PET or SPECT brain imaging.

A series of 4'-substituted phenyl-4-piperidinylmethanol and benzoyl-4-piperidine derivatives was synthesized as potential novel serotonin 5-HT2A receptor ligands that can be radiolabeled for in vivo brain imaging. Compounds were prepared by alkylation of 4-substituted benzoyl-4-piperidine with an iodo- or fluoro-substituted phenylalkyl halide followed by reduction with sodium borohydride. Potency of novel compounds was determined by in vitro radioreceptor affinity assays selective for serotonin 5-HT2A receptors. Potent compounds were further evaluated for selectivity at serotonin-2A versus 2C, 6, and 7, as well as dopamine D2 and adrenergic alpha1 and alpha2 receptors. The novel compound (4-fluorophenyl)-(1-[2-(4-fluorophenyl)ethyl]piperidin-4-yl])methanol was particularly promising with high 5-HT2A potency (K(i) = 1.63 nM) and >300-fold selectivity over other 5-HT receptor types.

Effects of norepinephrine and serotonin transporter inhibitors on hyperactivity induced by neonatal 6-hydroxydopamine lesioning in rats.

Consistent with their clinical effects in attention deficit-hyperactivity disorder (ADHD), the stimulants methylphenidate and amphetamine reduce motor hyperactivity in juvenile male rats with neonatal 6-hydroxydopamine (6-OHDA) lesions of the forebrain dopamine (DA) system. Since stimulants act on several aminergic neurotransmission systems, we investigated underlying mechanisms involved by comparing behavioral actions of d-methylphenidate, selective inhibitors of the neuronal transport of DA [GBR-12909 (1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-[3-phenylpropyl]piperazine dihydrochloride), amfonelic acid], serotonin [5-hydroxytryptamine (5-HT), citalopram, fluvoxamine], and norepinephrine (NE; desipramine, nisoxetine) in 6-OHDA lesioned rats. Selective dopamine lesions were made using 6-OHDA (100 microg, intracisternal) on postnatal day (PD) 5 after desipramine pretreatment (25 mg/kg, s.c.) to protect noradrenergic neurons. Rats were given test agents or vehicle, intraperitoneally, before recording motor activity for 90 min at PD 25 in a novel environment. d-Methylphenidate stimulated motor activity in sham controls and antagonized hyperactivity in lesioned rats. Selective DA transport inhibitors GBR-12909 and amfonelic acid greatly stimulated motor activity in sham control subjects, too, but did not antagonize hyperactivity in lesioned rats. In contrast, all selective 5-HT and NE transporter antagonists tested greatly reduced motor hyperactivity in 6-OHDA lesioned rats but did not alter motor activity in sham controls. The findings indicate that behavioral effects of stimulants in young rats with neonatal 6-OHDA lesions may be mediated by release of NE or 5-HT and support interest in using drugs that increase activity of norepinephrine or serotonin to treat ADHD.

Synthesis of cyclopentadienyltricarbonyl rhenium phenyltropanes by double ligand transfer: organometallic ligands for the dopamine transporter.

Cyclopentadienyltricarbonyl rhenium (CpRe(CO)(3)) systems can be prepared from ferrocenes and perrhenate by a double ligand transfer (DLT) reaction that gives reasonable yields and shows excellent functional group tolerance. We used this reaction for the direct preparation of CpRe(CO)(3)-phenyltropane conjugates. Such agents, when labeled with technetium-99m, might function as imaging agents for the dopamine transporter (DAT) system that would be useful for assessing the onset and severity of Parkinson's disease. Of the CpRe(CO)(3)-tropane conjugates prepared by the DLT reaction (as well as other analogues prepared by related methods), those substituted at the N-8 position seem most promising; their affinity for the DAT in all cases was high, and their ferrocene precursors for the DLT reaction can be prepared in a convenient manner. By contrast, the 3 beta-conjugates were poor DAT binders. The modular nature of these systems offers considerable flexibility that could be used to improve the binding characteristics of these compounds further.