Synthesis and dopamine transporter affinity of chiral 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-(2-hydroxypropyl)piperazines as potential cocaine abuse therapeutic agents

A series of optically pure phenyl-and non-phenyl-substituted 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-(2-hydroxypropyl)piperazines was synthesized and their binding affinity for dopamine transporter (DAT) was investigated. The analogues with a hydroxyl group in the S configuration were more selective for the DAT over the serotonin transporter (SERT) than the corresponding R enantiomers. Compound (+)-11 showed high affinity and selectivity for DAT over the SERT and, therefore, is a potential candidate for the development of a long-acting cocaine abuse therapeutic agent.     

Further exploration of 1-[2-[Bis-(4-fluorophenyl)methoxy]ethyl]piperazine (GBR 12909): role of N-aromatic,N-heteroaromatic,and 3-oxygenated N-phenylpropyl substituents on affinity for the dopamine and serotonin transporter

A series of N-aromatic, N-heteroaromatic, and oxygenated N-phenylpropyl derivatives of 1-(2-benzhydryloxyethyl)-piperazine and 1-[2-[bis-(4-fluorophenyl)methoxy]ethyl]piperazine, analogues of GBR 12909 (1a) and 12935 (1b), was synthesized and examined for their dopamine (DAT) and serotonin (SERT) transporter binding properties. One of these compounds, racemic 3-[4-(2-benzhydryloxyethyl)piperazin-1-yl]-1-(3-fluorophenyl)-propan-1-ol (33), had DAT affinity as good as, or better than, GBR 12909 and 12935, and was more selective for DAT over SERT than the GBR compounds. Both trans- (43) and cis- (47) (+/-)-2-(4-[2-[bis-(4-fluorophenyl)-methoxy]ethyl]piperazin-1-ylmethyl)-6-methoxy-1,2,3,4-tetrahydronaphthalen-1-ol had relatively good SERT selectivity and, as well, showed high affinity for SERT.     

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).     

Dual DAT/sigma1 receptor ligands based on 3-(4-(3-(bis(4-fluorophenyl)amino)propyl)piperazin-1-yl)-1-phenylpropan-1-ol

Ester analogs of (+/-)3-(4-(3-(bis(4-fluorophenyl)amino)propyl)piperazin-1-yl)-1-phenylpropan-1-ol were synthesized and evaluated for binding at DAT, SERT, NET, and sigma1 receptors, and compared to GBR 12909 and several known sigma1 receptor ligands. Most of these compounds demonstrated high affinity (K(i)=4.3-51 nM) and selectivity for the DAT among the monoamine transporters. S- and R-1-(4-(3-(bis(4-fluorophenyl)amino)propyl)piperazin-1-yl)-3-phenylpropan-2-ol were also prepared wherein modest enantioselectivity was demonstrated at the DAT. However, no enantioselectivity at sigma1 receptors was observed and most of the ester analogs of the more active S-enantiomer showed comparable binding affinities at both DAT and sigma1 receptors with a maximal 16-fold DAT/sigma1 selectivity.     

Synthesis and monoamine transporter affinity of front bridged tricyclic 3beta-(4'-halo or 4'-methyl)phenyltropanes bearing methylene or carbomethoxymethylene on the bridge to the 2beta-position

A series of front bridged tricyclic 3beta-(4'-halo or 4'-methyl)phenyltropanes bearing methylene or carbomethoxymethylene on the bridge to the 2beta-position was synthesized, and their binding affinities were determined in cells transfected to express human norepinephrine transporter (NET), serotonin transporter (SERT), and dopamine transporter (DAT) via competition binding assays. All compounds studied in this series exhibit a moderate to high potency at all three transporters with SERT or DAT selectivity. 3beta-(4'-iodo)phenyltropane bearing methylene on the bridge to the 2beta-position (24) presents a particularly attractive pharmacological profile, with very high SERT affinity (K(i) = 0.09 nM) and selectivity versus NET (65-fold) and DAT (94-fold).     

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).     

Design, synthesis, and characterization of a novel, 4-[2-(diphenylmethoxy)ethyl]-1-benzyl piperidine-based, dopamine transporter photoaffinity label

The dopamine transporter (DAT) has been implicated strongly in cocaine's reinforcing effects. Many derivatives of piperidine analogs of GBR 12909 have been developed and were found to be quite potent and selective for the DAT. In this regard, most of these derivatives were found to be much more selective for the DAT than conventional GBR compounds e.g. GBR 12909 when their selectivity was compared with the serotonin transporter (SERT). A brief structure-activity relationship (SAR) study has been carried out in the development of a novel photoaffinity ligand which illustrated the effect of the presence of a sterically bulky iodine atom next to the azido group in activity and selectivity for the DAT. This SAR study also led to the development of the compound 4 which is one of the most potent and selective blockers for the DAT known today. The photoaffinity ligand [125I]AD-96-129 was incorporated into the DAT molecule as was demonstrated by immunoprecipitation with serum 16 which is specific for DAT. This photolabeling was antagonized by DAT-specific blockers and was unaffected by specific SERT and norepinephrine transporter (NET) blockers indicating interaction of this novel ligand with the DAT.     

Further structure-activity relationship studies on 8-substituted-3-[2-(diarylmethoxyethylidenyl)]-8-azabicyclo[3.2.1]octane derivatives at monoamine transporters

The synthesis and structure–activity relationships of 8-substituted-3-[2-(diarylmethoxyethylidenyl)]-8-azabicyclo[3.2.1]octane derivatives were investigated at the dopamine transporter (DAT), the serotonin transporter (SERT) and norepinephrine transporter (NET). The rigid ethylidenyl-8-azabicyclic[3.2.1]octane skeleton imparted modestly stereoselective binding and uptake inhibition at the DAT. Additional structure–activity studies provided a transporter affinity profile that was reminiscent of the structure–activity of GBR 12909. From these studies, the 8-cyclopropylmethyl group has been identified as a unique moiety that imparts high SERT/DAT selectivity. In this study the 8-cyclopropylmethyl derivative 22e (DAT K_i of 4.0 nM) was among the most potent compounds of the series at the DAT and was the most DAT selective ligand of the series (SERT/DAT: 1060). Similarly, the 8-chlorobenzyl derivative 22g (DAT K_i of 3.9 nM) was found to be highly selective for the DAT over the NET (NET/DAT: 1358).     

Structural requirements for 2,4- and 3,6-disubstituted pyran biomimetics of cis-(6-benzhydryl-piperidin-3-yl)-benzylamine compounds to interact with monoamine transporters

In our effort to delineate novel pharmacophoric configuration of bioisosteric pyran versions of cis-(6-benzhydryl-piperidin-3-yl)-benzylamine derivatives in interacting with the monoamine transporter, further structure-activity relationship study was carried out. Both cis and trans 2,4- and 3,6-disubstituted derivatives were synthesized to determine the positional importance of N-substitution on affinity for monoamine transporters, that is the dopamine transporter (DAT), the serotonin transporter (SERT), and the norepinephrine transporter (NET) in rat brain. For that purpose, the potency of compounds was determined in competing for the binding of [(3)H]WIN 35,428, [(3)H]citalopram, and [(3)H]nisoxetine, respectively. Selected compounds were also evaluated for their activity in inhibiting the uptake of [(3)H]DA by DAT. Our binding results demonstrated potency in 3,6-disubstituted derivatives while 2,4-disubstituted derivatives failed to exhibit any appreciable binding affinity. Further structural exploration of the exocyclic N-atom in 3,6-disubstituted derivatives produced compounds potent at both DAT and NET. Compounds 16h and 16o with hydroxyl and amino groups in the phenyl moiety of the benzyl group produced the highest activity for the NET. In this regard, compound 16e with a methoxy substituent produced weak affinity at NET, which upon conversion into a hydroxyl functionality as in 16h produced potent affinity for the NET. Various indole derivatives displayed different interactions; the 5-substituted indole derivative 16n exerted potent affinity for NET, confirming the bioisosteric equivalence between this indole moiety and the phenyl-4-hydroxy group in 16h.     

Enantioselective synthesis of S-(+)-2beta-carboalkoxy-3alpha-[bis(4-fluorophenyl)methoxy]tropanes as novel probes for the dopamine transporter

Synthesis of a series of pure S-(+)-2beta-carboalkoxy-3alpha-[bis(4-fluorophenyl)methoxy]tropanes (>99% ee) was achieved by employing a chiral amine-induced asymmetric reaction of tropinone with methyl cyanoformate as the key step. In this series, all of the S-(+)-enantiomers were 2-fold more potent than their racemic mixtures and all displayed high-affinity binding for DAT (K(i)=13-40 nM). These data support previous findings of significant divergence in structural requirements for high-affinity DAT binding among tropane-based inhibitors. Furthermore, the 2-substituent in the 3alpha-[bis(4-fluorophenyl)methoxy]tropane series is well tolerated at the DAT but not at SERT (K(i)=690-2040 nM), or muscarinic M(1) receptors (K(i)=133-4380 nM) resulting in highly selective DAT ligands that may provide new leads toward a cocaine-abuse therapeutic.     

Synthesis of dopamine transporter selective 3-diarylmethoxymethyl-8-arylalkyl-8-azabicyclo[3.2.1]octane derivatives

A series of diarylmethoxymethyltropane-GBR hybrid analogues with all three possible stereochemical orientations at C3 were synthesized and evaluated at dopamine and serotonin transporters. The 3alpha derivatives were found to be the most potent compounds with the 3alpha-di(4-fluorophenyl)methoxymethyl-8-(3-phenylpropyl)-8-azabicyclo[3.2.1]octane 15b (Ki = 5 nM) being the most potent compound of the series. The corresponding 3-di(4-fluorophenyl)-methoxymethyl-8-(3-phenylpropyl)-8-azabicyclo[3.2.1]oct-2-ene 12b (Ki = 12 nM) was slightly less potent than the 3alpha-analogue, while the 3beta-di(4-fluorophenyl)methoxymethyl-8-(3-phenylpropyl)-8-azabicyclo[3.2.1]octane 23b (Ki = 78 nM) exhibited only modest affinity for the dopamine transporter. Only the 3alpha-analogue 15b (SERT/DAT = 48) exhibited higher SERT/DAT selectivity than GBR 12909. These results indicate that the dopamine transporter can tolerate some variability in proximity of the benzhydryl ether to the basic nitrogen atom of the tropane without loss in potency. In addition, the structure-activity data for these tropane-GBR 12909 hybrid analogues support previous findings that the stereochemical and conformational effects imparted by unsaturation at C3 are important for dopamine transporter selectivity over the serotonin transporter.     

DAT/SERT selectivity of flexible GBR 12909 analogs modeled using 3D-QSAR methods

The dopamine reuptake inhibitor GBR 12909 (1-{2-[bis(4-fluorophenyl)methoxy]ethyl}-4-(3-phenylpropyl)piperazine, 1) and its analogs have been developed as tools to test the hypothesis that selective dopamine transporter (DAT) inhibitors will be useful therapeutics for cocaine addiction. This 3D-QSAR study focuses on the effect of substitutions in the phenylpropyl region of 1. CoMFA and CoMSIA techniques were used to determine a predictive and stable model for the DAT/serotonin transporter (SERT) selectivity (represented by pK(i) (DAT/SERT)) of a set of flexible analogs of 1, most of which have eight rotatable bonds. In the absence of a rigid analog to use as a 3D-QSAR template, six conformational families of analogs were constructed from six pairs of piperazine and piperidine template conformers identified by hierarchical clustering as representative molecular conformations. Three models stable to y-value scrambling were identified after a comprehensive CoMFA and CoMSIA survey with Region Focusing. Test set correlation validation led to an acceptable model, with q(2)=0.508, standard error of prediction=0.601, two components, r(2)=0.685, standard error of estimate=0.481, F value=39, percent steric contribution=65, and percent electrostatic contribution=35. A CoMFA contour map identified areas of the molecule that affect pK(i) (DAT/SERT). This work outlines a protocol for deriving a stable and predictive model of the biological activity of a set of very flexible molecules.     

Synthesis and receptor binding properties of 2beta-alkynyl and 2beta-(1,2,3-triazol)substituted 3beta-(substituted phenyl)tropane derivatives

A series of 2beta-alkynyl and 2beta-(1,2,3-triazol)substituted 3beta-(substituted phenyl)tropanes were synthesized and evaluated for affinities at dopamine, serotonin, and norepinephrine membrane transporters using competitive radioligand binding assays. All tested compounds were found to exhibit nanomolar or subnanomolar affinity for the dopamine transporter (DAT). One of the most potent and selective compounds in the series was 3beta-(4-chlorophenyl)-2beta-(4-nitrophenylethynyl)tropane (10c) that possessed an IC(50) value of 0.9nM at the DAT and K(i) values of 230nM and 620nM at the norepinephrine transporter (NET) and serotonin transporter (5-HTT), respectively.     

Synthesis and biological evaluation of a series of novel N- or O-fluoroalkyl derivatives of tropane: potential positron emission tomography (PET) imaging agents for the dopamine transporter.

A series of novel fluoroalkyl-containing tropane derivatives was synthesized, and their binding affinities for the dopamine transporter (DAT), serotonin transporter (SERT), and norepinephrine transporter (NET) were determined via competitive binding assays. Among these derivatives, the fluoropropyl ester of beta-CIT (19), the fluoroethyl ester of beta-CIT (20), the N-fluoropropyl derivative of beta-CBT (12), and the fluoropropyl ester of beta-CMT (18) displayed higher affinity and greater selectivity for the DAT versus SERT and NET than FP-CIT, which indicates that they are attractive candidates for the development of (18)F-labeled PET imaging agents for the DAT.     

Synthesis and monoamine transporter binding properties of 2beta-[3'-(substituted benzyl)isoxazol-5-yl]- and 2beta-[3'-methyl-4'-(substituted phenyl)isoxazol-5-yl]-3beta-(substituted phenyl)tropanes

A series of 2beta-[3'-(substituted benzyl)isoxazol-5-yl]- and 2beta-[3'-methyl-4'-(substituted phenyl)isoxazol-5-yl]-3beta-(substituted phenyl)tropanes were prepared and evaluated for affinities at dopamine, serotonin, and norepinephrine transporters using competitive radioligand binding assays. The 2beta-[3'-(substituted benzyl)isoxazol-5-yl]-3beta-(substituted phenyl)tropanes (3a-h) showed high binding affinities for the dopamine transporter (DAT). The IC(50) values ranged from 5.9 to 22nM. On the other hand, the 2beta-[3'-methyl-4'-(substituted phenyl)isoxazol-5-yl]-3beta-(substituted phenyl)tropanes (4a-h), with IC(50) values ranging from 65 to 173nM, were approximately 3- to 25-fold less potent than the corresponding 2beta-[3'-(substituted benzyl)isoxazol]tropanes. All tested compounds were selective for the DAT relative to the norepinephrine transporter (NET) and serotonin transporter (5-HTT). 3Beta-(4-Methylphenyl)-2beta-[3'-(4-fluorobenzyl)isoxazol-5-yl]tropane (3b) with IC(50) of 5.9nM at the DAT and K(i)s of 454 and 113nM at the NET and 5-HTT, respectively, was the most potent and DAT-selective analog. Molecular modeling studies suggested that the rigid conformation of the isoxazole side chain in 4a-h might play an important role on their low DAT binding affinities.     

Identification of a butyrophenone analog as a potential atypical antipsychotic agent: 4-[4-(4-chlorophenyl)-1,4-diazepan-1-yl]-1-(4-fluorophenyl)butan-1-one

The synthesis and exploration of novel butyrophenones have led to the identification of a diazepane analogue of haloperidol, 4-[4-(4-chlorophenyl)-1,4-diazepan-1-yl]-1-(4-fluorophenyl)butan-1-one (compound 13) with an interesting multireceptor binding profile. Compound 13 was evaluated for its binding affinities at DA subtype receptors, 5HT subtype receptors, H-1, M-1 receptors and at NET, DAT, and SERT transporters. At each of these receptors, compound 13 was equipotent or better than several of the standards currently in use. In in vivo mouse and rat models to evaluate its efficacy and propensity to elicit catalepsy and hence EPS in humans, compound 13 showed similar efficacy as clozapine and did not produce catalepsy at five times its ED(50) value.     

Synthesis, in vitro characterization, and radiolabeling of reboxetine analogs as potential PET radioligands for imaging the norepinephrine transporter

Six new (S,S)-enantiomers of reboxetine derivatives were synthesized and their binding affinities were determined via competition binding assays in cells expressing the human norepinephrine transporter (NET), serotonin transporter (SERT) or dopamine transporter (DAT). All six compounds prepared exhibit high affinity for the NET (K(i)相似文献   

Design, synthesis, and preliminary SAR study of 3- and 6-side-chain-extended tetrahydro-pyran analogues of cis- and trans-(6-benzhydryl-tetrahydropyran-3-yl)-benzylamine

In our effort to further understand interaction of novel pyran derivatives with monoamine transporters, we have designed, synthesized, and biologically characterized side-chain-extended derivatives of our earlier developed cis- and trans-(6-benzhydryl-tetrahydro-pyran-3-yl)-benzylamine derivatives. Both 3- and 6-position extensions were explored. All synthesized derivatives were tested for their affinities for the dopamine transporter (DAT), serotonin transporter (SERT), and norepinephrine transporter (NET) in the brain by measuring their potency in inhibiting the uptake of [(3)H]DA, [(3)H]5-HT, and [(3)H]NE, respectively. Compounds were also tested for their binding affinity at the DAT by their ability to inhibit binding of [(3)H]WIN 35, 428. The results indicated that extension at the 3-position resulted in loss of activity compared to the original compound I. On the other hand, extension at the 6-position resulted in improvement of activity in the compound cis-12 by 2-fold over the parent compound I indicating favorable interaction. In addition, two glycoside derivatives were designed, synthesized, and biologically characterized. The glycosidic trans-isomer 24 exhibited highest potency for the NET in the current series of compounds.     

Development of new brain imaging agents based upon nocaine-modafinil hybrid monoamine transporter inhibitors

11C-labeled (+)-trans-2-[[(3R,4S)-4-(4-chlorophenyl)-1-methylpiperidin-3-yl]methylsulfanyl]ethanol ([11C]5) and (+)-trans-2-[[(3R,4S)-4-(4-chlorophenyl)-1-methylpiperidin-3-yl]methylsulfanyl]-1-(piperidin-1-yl)ethanone ([11C]6) were synthesized and evaluated as new imaging agents for the norepinephrine transporter (NET). [11C]5 and [11C]6 display high affinity for the NET in vitro (Ki = 0.94 and 0.68 nM, respectively) and significant selectivity over the dopamine (DAT) and serotonin transporters (SERT). Because of their high affinity and favorable transporter selectivities we speculated that these ligands might serve as useful PET agents for imaging NET in vivo. Contrary to our expectations, both of these ligands provided brain images that were more typical of those shown by agents binding to the DAT.     

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.