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We have prepared azabicyclo[3.2.1] derivatives (C-3-substituted tropanes) that bind with high affinity to the dopamine transporter and inhibit dopamine reuptake. Within the series, 3-[2-[bis-(4-fluorophenyl)methoxy]ethylidene]-8-methyl-8-azabicyclo[3.2.1]octane (8) was found to have the highest affinity and selectivity for the dopamine transporter. These azabicyclo[3.2.1] (bridged piperidine) series of compounds differ from the well-known benztropines by a 2-carbon spacer between C-3 and a diarylmethoxy moiety. Interestingly, these new compounds demonstrated a much lower affinity for the muscarinic-1 site, at least a 100-fold decrease compared to benztropine. Replacing N-methyl with N-phenylpropyl in two of the compounds resulted in a 3-10-fold increase in binding affinity for the dopamine transporter. However, those compounds lost selectivity for the dopamine transporter over the serotonin transporter. Replacement of the ether oxygen in the diarylmethoxy moiety with a nitrogen atom gave relatively inactive amines, indicating the important role which is played by the ether oxygen in transporter binding. Reduction of the C-3 double bond in 8 gave 3 alpha-substituted tropanes, as shown by X-ray crystallographic analyses of 11, 12, and 19. The 3 alpha-substituted tropanes had lower affinity and less selectivity than the comparable unsaturated ligands.

A convenient enantioselective synthesis of (1R,5R,9R)- and (1S,5S, 9S)-9-alkyl-2-benzyl-6,7-benzomorphans (2a-c) which starts with naphthaldehyde is described. These compounds were designed to gain additional information on the structure-sigma binding relationship of the 6,7-benzomorphan class of sigma ligands. In contrast to pentazocine and most 6,7-benzomorphans, the (1R,5R,9R)-isomers of 2a-c showed greater affinity for the sigma(1) receptor than the (1S, 5S,9S)-isomers. Despite reversal of enantioselectivity at the sigma(1) sites, moderate affinity and enantioselectivity at the sigma(2) sites [greater affinity for (1R,5R,9R)-isomers than (1S,5S, 9S)-isomers] were maintained. A comparison of the binding affinities of 2a-c to the more conformationally flexible trans-2-alkyl-1-benzaminoethyl-1,2-dihydronaphthalenes (10a-c) suggested that the relatively rigid structure of 2a-c played an important part in their sigma(1) binding properties. These compounds, particularly (1R,5R,9R)-2-benzyl-9-methyl-6,7-benzomorphan [(-)-2a], which has a K(i) value of 0.96 nM, will be useful in further characterization of the sigma(1) receptor.

9-[3-(cis-3,5-Dimethyl-1-piperazinyl)propyl]carbazole (rimcazole) has been characterized as a sigma receptor antagonist that binds to the dopamine transporter with moderate affinity (K(i) = 224 nM). Although the binding affinities at the dopamine transporter of rimcazole and cocaine are comparable, rimcazole only depressed locomotor activity in mice and antagonized the stimulant effects produced by cocaine. The neurochemical mechanisms underlying the attenuation of cocaine's effects are not understood, although interaction at a low affinity site/state of the dopamine transporter has been suggested. To explore further this class of compounds, a series of rimcazole analogues was designed and synthesized. Displacement of [(3)H]WIN 35,428 binding at the dopamine transporter in rat caudate-putamen revealed that aromatic substitutions on rimcazole were not well tolerated, generally, with significant reductions in affinity for the 3,6-dibromo (5; K(i) = 3890 nM), 1,3, 6-tribromo (6; K(i) = 30300 nM), 3-amino (8; K(i) = 2400 nM), and 3, 6-dinitro (9; K(i) = 174000 nM) analogues. The N-phenylpropyl group was the only terminal piperazine nitrogen substituent that retained moderate affinity at the dopamine transporter (11; K(i) = 263 nM). Analogues in which the carbazole ring was replaced with a freely rotating diphenylamine moiety were also prepared. Although the diphenylamino analogue in which the terminal piperazine nitrogen was unsubstituted, as in rimcazole, demonstrated relatively low binding affinity at the dopamine transporter (24; K(i) = 813 nM), the N-phenylpropyl analogue was found to have the highest affinity for the dopamine transporter within the series (25; K(i) = 61.0 nM). All of the analogues that had affinity for the dopamine transporter inhibited [(3)H]dopamine uptake in synaptosomes, and potencies for these two effects showed a positive correlation (r(2) = 0.7731, p = 0.0018). Several of the analogues displaced [(3)H]paroxetine from serotonin transporters with moderate to high affinity, with the N-phenylpropyl derivative (11) having the highest affinity (K(i) = 44.5 nM). In contrast, none of the analogues recognized the norepinephrine transporter with an affinity of <1.3 microM. Binding affinities for sigma(1) and sigma(2) receptors were also determined, and several of the compounds were more potent than rimcazole with affinities ranging from 97 nM to >6 microM at sigma(1) sites and 145 to 1990 nM at sigma(2) sites. The compound with the highest affinity (25) at sigma(1) sites was also the compound with highest affinity at the dopamine transporter. These novel rimcazole analogues may provide important tools with which to characterize the relationship between the low affinity site or state of the dopamine transporter, sigma receptors, and their potential roles in modulating cocaine's psychostimulant actions.

sigma Receptors have been the focus of extensive studies because of their potential functional role in several important physiological and biochemical processes. To further evaluate the properties of sigma receptors, especially sigma-1 and sigma-2 subtypes, we have synthesized a series of N,N'-disubstituted piperazine compounds (1-32). The design of these compounds was based upon the early structure-activity relationship (SAR) studies of the minimum structural requirements of a molecule necessary to elicit sigma receptor binding activity. In the N-(3-phenylpropyl)piperazine series, compounds with the ethylenediamine moiety (8-11, 15-17) showed 6-20-fold higher affinity for sigma-1 and 2-40-fold higher affinity for sigma-2 relative to their corresponding amides (1-7). The (m-nitrophenethyl)piperazine 10 exhibits a subnanomolar affinity for the sigma-1 site, whereas the corresponding o-nitro compound 9 shows the highest affinity for the sigma-2 site (Ki = 4.9 nM). Compounds with a free amino terminus were designed as precursors for use as bioconjugated affinity compounds. Some of these compounds displayed high affinity for sigma-1 and moderate affinity for sigma-2 sites and are currently used for the purification and characterization of the receptor subtypes.

The discovery of a series of novel halogenated arylsulfonamides (HAS) as new sigma receptor binding tumor imaging agents is described. Several substituted halogenated sulfonamides have been prepared and characterized. Target compounds were examined for their affinity for sigma1 and sigma2 receptor subtypes using guinea pig brain membranes and rat liver membranes, respectively. A number of substituted halogenated sulfonamides displayed subnanomolar affinities for sigma1 sites and low nanomolar affinities for sigma2 subtype receptors. A limited structure-activity relationship study of this chemical series is discussed. The radioiodination (I-125) of one congener member (4-[125I]iodo-N-[2-(1'-piperidinyl)ethyl]benzenesulfonamide, 4-[125I]IPBS) was accomplished in high yields. The in vitro competition binding studies of 4-[125I]IPBS in guinea pig brain membranes with sigma receptor binding ligands confirmed its sigma pharmacology. The rank order of potency was BD1008 (N-[2-(3, 4-dichlorophenyl)ethyl]-N-methyl-2-(1-pyrrolidinyl)ethylamine) > 4-IPBS > haloperidol > (+)-pentazocine > DTG (1, 3-di-o-tolylguanidine) > (-)-pentazocine. The inhibition constants (IC50) were 0.70, 1.46, 6.28, 10.4, 87.2, and 152 nM, respectively, and are consistent with labeling of sigma1 receptors. The tumor imaging potential of 4-[125I]IPBS was studied in C57 black mice bearing B16 melanoma xenograft. A high tumor uptake of 4-[125I]IPBS was observed (7.40% ID/g) at 1 h postinjection. The wash out of activity from the tumor was slow at 6 h postinjection (7.22% ID/g). The tumor also had the highest amount of radioactivity (1.54% ID/g) at 24 h postinjection. These results demonstrate that radiohalogenated benzenesulfonamides could be a potentially useful class of compounds in nuclear oncologic scintigraphy.

Cocaine has been reported to bind to the dopamine transporter in a biphasic fashion, and it has been hypothesized that the low-affinity component may play a modulatory role in cocaine's psychomotor stimulant effects. In an effort to gain further insight into the roles of the two sites, we have prepared a series of irreversible ligands based on rimcazole (9-[3-(cis-3,5-dimethyl-1-piperazinyl)propyl]carbazole, 2), a compound that has been postulated to bind only to the low-affinity site. The alkylating moiety (isothiocyanate) is attached to the distal nitrogen of the piperazine ring via alkyl chains of varying lengths or directly attached to one of the aromatic groups. It was found that substitution on the piperazine nitrogen caused an initial decrease in affinity that was recovered as the alkyl chain length increased. Importantly, the analogue 16, with the highest affinity for the dopamine transporter (DAT), binds in a monophasic and irreversible manner, as evidenced by the greatly diminished binding of [3H]WIN 35,428 in tissue that had been preincubated with the ligand and then thoroughly washed using centrifugation. The dose-dependent reduction in Bmax was accompanied by a concentration-related decrease in KD values. This shift in KD to a lower value suggests that the preincubation with 16 produced a preferential irreversible binding to the low-affinity [3H]WIN 35,428 site on the dopamine transporter. These ligands may prove to be important tools with which to study the significance of the low-affinity site on the DAT. Since rimcazole does not share the behavioral profile of cocaine, and in fact appears to play a modulatory role, these compounds may provide leads for a novel cocaine-abuse treatment.

sigma-Receptors have recently been shown to be expressed in a variety of human tumor cells. In an attempt to prepare 99mTc chelates that would bind to sigma-receptors and be useful for imaging sigma-receptor-positive tumors, we have synthesized and characterized a bisaminothiol (BAT) chelate appended with a sigma-receptor pharmacophore. The synthesis of target ligand VII was accomplished in three steps starting from bicyclic imidazolidino[1,2-d]dithiazapine. The labeling of the BAT ligand with 99mTc was carried out in high yields (> 80%) using stannous tartarate as a reducing agent, resulting in the target sigma-receptor-binding chelate [99mTc]BAT-EN6, III. Similarly, 99gTc chelate with ligand VII was prepared from ammonium pertechnetate by reduction with stannous tartarate. 99nTc-radiolabeled chelate was purified by reversed phase HPLC, and cell binding with human breast ductal carcinoma (T47D) was performed. A high degree of specific binding (90-97%) was obtained when sigma-receptor ligands such as halogenated phenylethylenediamines were used to determine nonspecific binding. A modest affinity dose-dependent inhibition of binding was found with BD1008, I, and 4-IPEMP, II (IC50 = 47 +/- 2 and 59 +/- 5 nM, respectively), known sigma-ligands. No specific binding was found with [99mTc]BAT, VIII [without appended sigma-pharmacophore (N-alkyl-substituted ethylenediamine)], showing that biological activity resulted from the pendent pharmacophore. 99gTc complex was found to be a potent inhibitor (Ki = 42.7 +/- 8.5 nM) of [3H]DTG binding in guinea pig brain membranes. Scatchard analysis of [99mTc]BAT-EN6 (spiked with [99gTc]BAT-EN6) binding in T47D breast cancer cells showed a saturable binding, with a Kd of 43.5 +/- 14.7 nM and a Bmax of 3121 +/- 130 fmol/(mg of protein). A biodistribution study of [99mTc]BAT-EN6 chelates in Sprague Dawley rats showed hepatic clearance, as expected. A blocking study at 4 h postinjection using 2 mumol of BD1008 with [99mTc]BAT-EN6 showed a significant decrease of radiopharmaceutical in liver (15.32 vs 22.31% ID/organ) and kidney (1.01 vs 2.21% ID/ organ), organs known to possess high concentrations of sigma-receptors. These results imply that [99mTc]BAT-EN6 binds with high affinity to sigma-receptors expressed in human breast tumor cells, and it may be useful for imaging breast cancer.

A series of 2'- and 3'-substituted and 3',3"-disubstituted 3 alpha-(diphenylmethoxy)tropane analogs were designed and synthesized as novel probes for the dopamine transporter. All the analogs were evaluated for displacement of [3H]WIN 35,428 binding at the dopamine transporter and for inhibition of [3H]dopamine uptake in rat caudate putamen. Compounds were observed to monophasically displace [3H]WIN 35,428 binding to the dopamine transporter with affinities of 21.6-1836 nM (Ki). Generally, meta-substituted compounds were more potent than benztropine and equipotent to or slightly less potent than their previously reported para-substituted homologs in inhibiting [3H]WIN 35,428 binding. However, these same meta-substituted analogs were typically less potent than the 4'-substituted analogs in inhibiting [3H]dopamine uptake. Ortho-substituted analogs were generally less potent in both binding and inhibition of uptake at the dopamine transporter than either benztropine or other aryl-substituted homologs. The analogs were also tested for binding at norepinephrine and serotonin transporters as well as muscarinic m1 receptors. None of the compounds in the present study bound with high affinity to either the norepinephrine or serotonin transporters, but all bound to muscarinic m1 receptors with high affinity (K1 = 0.41-2.52 nM). Interestingly, 3'-chloro-3 alpha-(diphenylmethoxy)tropane (5c) produced effects like cocaine in animals trained to discriminate 10 mg/kg cocaine from saline, unlike its 4'-Cl homolog and all of the previously evaluated benztropine analogs. Further evaluation of compound 5c and the other benztropine analogs will undoubtedly prove useful in the elucidation of the role of the dopamine transporter in the reinforcing effects of cocaine and the ultimate identification of a cocaine-abuse treatment.

A series of aryl-monosubstituted arylacetamides (4-9) and arylethylenediamine (10-18) compounds were synthesized based on the structure of the high-affinity sigma ligand N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(1-pyrrolidinyl)ethylamine (2). These compounds were prepared to evaluate the effect of aromatic substitution patterns on sigma-1 and sigma-2 receptor binding affinity and selectivity. The data indicate that 10-18 possessed higher affinity than 4-9 for both sigma sites, especially when substituted with an electron-withdrawing group. The diamine compounds 10-18 were selective for sigma-1 binding sites, whereas the arylacetamide compounds 4-9 generally exhibited an increased selectivity for sigma-2 sites compared to sigma-1. No clear pattern between the orientation of aromatic substituents and the sigma binding activity was observed.

The determination of the structure and function of the sigma receptor subtypes and their physiological role(s) has been impeded by the unavailability of selective ligands. We have developed a new class of sigma subtype selective receptor ligands that are (E)-8-benzylidene derivatives of the synthetic opioid (+/-)-, (+)-, and (-)-2-methyl-5-(3-hydroxyphenyl)morphan-7-one (1). The derivatives can be prepared by reaction of 1, (+)-1, and (-)-1 with the appropriate benzaldehyde under Claisen-Schmidt conditions. Incorporation of substituted (E)-8-benzylidene moieties onto the 7-keto precursor of (+)-2-methyl-5-(3-hydroxyphenyl)morphan, (+)-1, produces compounds (-)-2 through (-)-7 (5.8-32.0 nM, sigma 1), which have between a 25- and 131-fold increase in affinity for the sigma 1 receptor subtype relative to the keto precursor (+)-1 (Ki = 762 nM, sigma 1). Compound (-)-2 is the most selective of this group (16-fold) for the sigma 1 subtype versus sigma 2. Substitution of an (E)-8-benzylidene moiety onto the 7-keto precursor of (-)-2-methyl-5-(3-hydroxyphenyl)morphan, (-)-1, produces compounds (+)-2-(+)-9 (6.4-52.6 nM, sigma 2), which have at least a 475-3906-fold increase in affinity for the sigma 2 receptor subtype relative to the keto precursor (-)-1 (Ki = 25 x 10(3) nM). This enhancement of sigma 2 receptor affinity is accompanied by substantial selectivity of all of these dextrorotatory products for the sigma 2 relative to the sigma 1 subtype (32-238-fold), and thus, they are among the most sigma 2 selective compounds currently known. Furthermore, the sigma 1 subtype is highly enantioselective for the levorotatory isomers, (-)-2-(-)-7 (41-1034-fold), whereas the sigma 2 subtype is only somewhat enantioselective for the dextrorotatory isomers, (+)-2-(+)-7 (2.6-9.3-fold). All of these derivatives retain substantial affinity for the mu opioid receptor. Despite the high affinity of the dextrorotatory derivatives for the mu opioid receptor, the high affinity and selectivity for sigma 2 over sigma 1 sites will surely prove beneficial as tools for the delineation of the function and physiological role of sigma 2 receptors.

The synthesis and sigma 1 and sigma 2 binding properties of several 1'- and 3'-halo- and 1',3'-dihalo-substituted analogues of (+)-N-benzyl- and (+)- and (-)-N-dimethylallyl-N-normetazocine are presented. Structure-activity relationship analyses of the binding data showed that halogen substitution at the 1'-position of these N-substituted N-normetazocine analogues had little effect on sigma 1 binding affinity, whereas 3'-halo substitution as well as 1',3'-dihalo substitution resulted in a reduction of affinity. sigma 2 affinity was increased by the presence of a 3'-bromo substituent in this series of (+)-N-substituted N-normetazocines.

The synthesis and sigma 1 and sigma 2 binding properties of several (+)- and (-)-2-benzyl- and 2-dimethylallyl-2'-substituted-5,9 alpha-dimethyl-6,7-benzomorphans (3 and 4) are presented. In agreement with previously reported binding data for 2-substituted 5,9 alpha-dimethyl-2'-hydroxy-6,7-benzomorphans (N-substituted-N-normetazocine), all (1S,5S,9S)-(+)-isomers showed higher affinity for the sigma 1 site than the corresponding (1R,5R,9R)-(-)-isomers. Replacement of the 2'-hydroxy group of (+)-2-benzyl-5,9 alpha-dimethyl-2'-hydroxy-6,7-benzomorphan [(+)-1f] with a 2'-NH2 and 2'-N(CH3)2 [(+)-3b and (+)-3c, respectively] had only a small effect on the sigma 1 Ki values. Changing the 2'-hydroxy group of (+)-1f to an H, F, Cl, Br, I, NHAc, or NHSO2CH3 resulted in a 5-fold or greater loss in potency. In contrast, replacement of the 2'-hydroxy group of (+)-2-(dimethylallyl)-5,9 alpha-dimethyl-2'-hydroxy-6,7-benzomorphan [(+)-1b, (+)-pentazocine] with a 2'-H or 2'-F group resulted in a 2-fold increase in potency. Conversion of (+)-1f to its 2'-desoxy analogue (+)-2d resulted in a 27.5-fold loss in affinity. This suggests that (+)-1f and other N-substituted benzomorphan analogues may be binding to single sigma 1 receptors in a different way or to different sigma 1 receptors. (-)-Pentazocine [(-)-1b] and its 2'-fluoro analogue, (-)-2-(dimethylallyl)-5,9 alpha-dimethyl-2'-fluoro-6,7-benzomorphan [(-)-4a] showed the highest potency for the sigma 2 binding site.

sigma 1 receptor ligands have potential pharmacological significance as antipsychotic drugs, as tools in the study of drug-induced motor function disorders, and as radiopharmaceutical imaging agents for the noninvasive imaging of malignant tumors in human subjects. A series of substituted N-benzyl-N-normetazocines were synthesized and their binding affinity at the sigma 1 receptor evaluated in order to examine the details of the structure--affinity relationships (SAR) of a previously determined high-affinity lead compound, (+)-cis-N-benzyl-N-normetazocine (Ki = 0.67 nM). Variation in the benzyl substituents of these compounds produced a 1590-fold range in affinity at the sigma 1 receptor from the unsubstituted benzyl analog to the lowest affinity p-tert-butylbenzyl analog (Ki = 1066 nM). The nanomolar binding affinity for the sigma 1 receptor of (+)-cis-N-(4-fluorobenzyl)-N-normetzocine suggests that this analog may be a useful PET imaging agent.

A series of polyamines based on the high affinity sigma receptor ligand N-[2-(3,4-dichlorophenyl)-ethyl]-N-methyl-2-(1-pyrrolidinyl)ethylamine (3) were developed and evaluated for their binding characteristics at sigma-1 and sigma-2 receptor subtypes. The data indicated that a considerable degree of structural variation is possible while still retaining nanomolar affinity at sigma receptors. As the structure of the polyamines was varied, their binding at sigma-1 and sigma-2 subtypes showed quite different and in some cases opposite trends, supporting the belief that these are pharmacologically distinct entities. Polyamines containing two nitrogen atoms showed optimal binding at both sigma-1 and sigma-2 receptor subtypes. Although additional nitrogen atoms resulted in decreased affinity at sigma-1 and sigma-2 subtypes, an increase in selectivity for sigma-2 subtypes was evident; the parent 3 showed greater selectivity for sigma-1 subtypes. Internitrogen spacings had a large effect on binding affinity and subtype selectivity. For example, the difference between N-[3-(1-pyrrolidinyl)propyl]-N'-(3,4-dichlorobenzyl)-N,N'- dimethylethylenediamine (8) [K(i) = 29.9 nM at sigma-1 receptor and 18.3 nM at sigma-2 receptor] to N-[3-(1-pyrrolidinyl)propyl]-N'-(3,4-dichlorobenzyl)- N,N'-dimethylethylenediamine (10) [K(i) = 1.49 nM at sigma-1 receptor and 12.1 nM at sigma-2 receptor] illustrates the importance of internitrogen spacing. Triamines 11 and 13 [Ki(sigma-2)/K(i)(sigma-1) = 0.19 and 0.10, respectively] containing the N-N-N-Ar spacings 3-3-2 and 4-4-2, proved to be the most sigma-2 subtype selective of the 15 polyamines examined in this study. The N-N-N spacings appear to be an important factor in their sigma-2 subtype selectivity. These compounds will serve as templates in the design of still further sigma-2 subtype selective ligands. The pyrrolidine ring (present in most of the polyamines tested in this series) proved to be an important recognition site for sigma receptor binding activity. Furthermore, alkyl substitution also appears to be important since the stripped down polyamines N-[2-(3,4-dichlorophenyl)ethyl]ethylenediamine (15) and N1-[2-(3,4-dichlorophenyl)ethyl]diethylenetriamine (16) exhibited relatively low binding affinity.

As a continuation of our earlier study (J. Med. Chem. 1992, 35, 4334-4343) we conformationally restricted the sigma-receptor ligand 2-(1-pyrrolidinyl)-N-[2-(3,4-dichlorophenyl)ethyl]-N-methylethylamine (1) by incorporating it into a series of homologous piperazines 3-9 and homopiperazines 10 and 11, diazabicyclononanes and decanes, bridgehead bicyclooctanes and nonanes as well as other miscellaneous compounds. sigma-Receptor binding affinities were obtained using [3H](+)-pentazocine in guinea pig brain membrane sigma 1 sites. The studies suggest that the nitrogen lone pair orientation found in the piperazines affords the strongest binding interaction. Other nitrogen lone pair orientations or compounds representing unlikely staggered conformations of 1 [ as in 4-[2-(3,4-dichlorophenyl)ethyl]-1,4-diazabicyclo[3.2.2]nonane (16)] show very weak sigma interaction. Comparison of the binding data of different N-substituted homologues of 1 with those of the 1-[2-(3,4-dichlorophenyl)ethyl]-4-alkylpiperazines suggests that the two nitrogen atoms of 1 are working in opposition to one another in terms of their sensitivity to steric bulk. The high binding affinity of the 1,4-diazabicyclo[4.3.0]nonanes 12 suggests that these may approximate the methyl and pyrrolidine ring conformations found in 1 when it is bound to the sigma receptor. Compound 12 exhibited a 4-fold enantioselectivity favoring (+)-12. The synthesis of 6,7-dichloro-2-[[2-(1-pyrrolidinyl)ethyl]amino]tetralin (19) and its desmethyl derivative 20 permitted constraint of the 3,4-dichlorophenyl and N-methyl moieties of 1 into a gauche orientation. The binding data suggests that this conformation in 1 favors strong binding interaction at sigma-receptors. sigma-Receptor Ki's ranged from 0.55 nM for 1-[2-(3,4-dichlorophenyl)ethyl]-4-n-butylpiperazine (7) to 654 nM for 16. Overall comparison of the results indicate that 1 is subject to considerable conformational freedom and suggests that the sigma receptor is not subject to rigid stereochemical restraints with 1. These results add to our earlier study where we restrained 1 using simple monocyclic heterocycles.

2-, 3-, and 4-idophenyl derivatives of the high-affinity sigma ligand N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(1-pyrrolidinyl)ethylamine (1) were synthesized in two to four steps starting from N-methyl-2-(1-pyrrolidinyl)ethylamine. These compounds were evaluated for their capacity to label both sigma 1 and sigma 2 subtypes in vitro. sigma-1 binding affinity was determined by measuring competition with [3H]-(+)-pentazocine binding to guinea pig brain membranes while sigma 2 binding was evaluated through competition with [3H]DTG binding to rat liver membranes in the presence of excess dextrallorphan. The binding data revealed that N-[2-(3-iodophenyl)ethyl]-N-methyl-2-(1-pyrrolidinyl)ethylamine (2) and N-[2-(4-iodophenyl)ethyl]-N-methyl-2-(1-pyrrolidinyl)ethylamine (3) displayed almost identical binding affinity at sigma 1 sites to the parent compound 1. This suggests that the 3- or 4-iodo group can effectively substitute for the 3,4-dichloro substituents of 1. In this series of compounds, Ki's at the sigma 1 site varied from 2.0 nM for N-(4-iodobenzyl)-N-methyl-2-(1-pyrrolidinyl)ethylamine (6) to 26.6 nM for N-(2-iodobenzyl)-N-methyl-2-(1-pyrrolidinyl)ethylamine (4). Ki's for sigma 2 site ranged from 8.1 nM for 1 to 220 nM for N-(3-bromobenzyl)-N-methyl-2-(1-pyrrolidinyl)ethylamine (11) while the sigma 2/sigma 1 ratio varied from 1.8 for 4 to 25 for 11. Comparing halogen substitution, the trend Cl = I > Br > F was observed for binding affinity at sigma 1 sites; no such trend was observed at sigma 2 sites. On the basis of the binding data, compounds 2 and 3 were selected for labeling with 123I. Thus, treatment of the corresponding 3- and 4-(tributylstannyl) intermediates (7 and 8) with Na123I in the presence of excess CH3CO3H furnished [123I]-2 and [123I]-3 in up to 70% radiochemical yield. Preliminary in vitro binding with [123I]-3 indicated up to 97% specific binding with guinea pig brain membranes.

Unlabeled fluoro- and iodo-substituted ligands exhibiting very high affinity and selectivity for sigma receptors were synthesized based on three different structural classes of sigma receptor ligands. These compounds were evaluated for sigma receptor affinity and specificity in order to assess their potential as PET/SPECT imaging agents. Thus, (+)- and (-)-N-(5-fluoro-1-pentyl)normetazocines [(+)- and (-)-4] based on the (+)-benzomorphan class of sigma ligands were synthesized via N-alkylation of optically pure (+)- and (-)-normetazocine with 5-[(methylsulfonyl)oxy]-1-pentyl fluoride (11). (+)- and (-)-4 displaced [3H](+)-3-PPP with Ki values of 0.29 and 73.6 nM and [3H](+)-pentazocine with Ki values of 10.5 and 38.9 nM, respectively. The second class of PET/SPECT ligands was based upon the N-(arylethyl)-N-alkyl-2-(1-pyrrolidinyl)ethylamine class of sigma ligands; N-[2-(3,4-dichlorophenyl)-1-ethyl]-N-(3-fluoro-1-propyl)-2-(1- pyrrolidinyl)ethylamine (5) was obtained via N-alkylation of N-[2-(3,4-dichlorophenyl)-1-ethyl]-2-(1-pyrrolidinyl)ethylamine (14) with 3-fluoropropyl p-toluenesulfonate. 5 exhibited Ki values of 4.22 and 5.07 nM for displacement of [3H](+)-3-PPP and [3H](+)-pentazocine, respectively, comparable with the parent N-propyl compound. Attempts to synthesize N-[2-(3,4-dichlorophenyl)-1-ethyl]-N-[3- [(methylsulfonyl)oxy]-1-propyl]-2-(1-pyrrolidinyl)ethylamine (26), a precursor to 5 that could conceivably be converted to [18F]-5 by treatment with 18F-, proved unsuccessful. The sequence of regioselective nitration, catalytic hydrogenation, and diazotization followed by NaI quench of N-[2-(3,4-dichlorophenyl)-1-ethyl]-N-methyl-2-(1- pyrrolidinyl)ethylamine (2) afforded the iodinated ethylenediamine N-[2-(2-iodo-4,5-dichlorophenyl)-1-ethyl]-N-methyl-2-(1- pyrrolidinyl)ethylamine (8), a potential SPECT ligand for sigma receptors. This compound showed an affinity of 0.54 nM ([3H](+)-3-PPP) comparable with the parent compound 2 (Ki = 0.34 nM, [3H](+)-3-PPP). Ligand 8 exhibited a similar potency against [3H](+)-pentazocine. The third class of high-affinity sigma receptor ligands was rationalized based on rearrangement of the bonds in ethylenediamine 2 to give 1-[2-(3,4-dichlorophenyl)-1-ethyl]-4-(1-propyl)piperazine (3). This compound exhibited very high affinity (Ki = 0.31 nM, [3H](+)-3-PPP) and selectivity for sigma receptors.(ABSTRACT TRUNCATED AT 400 WORDS)

By synthesizing and testing a part-structure, N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(1-pyrrolidinyl)ethylamine (3), derived from our previously reported high affinity sigma receptor ligands (1S,2R)-(-)-N-[2-(3,4-dichlorophenyl)-ethyl]-N-methyl-2-(1- pyrrolidinyl)cyclohexylamine [(-)-2] and (+)-2, we have identified a novel class of superpotent (subnanomolar affinity) sigma ligands specific for the sigma receptor labeled by [3H]-(+)-3-PPP. When 3 was tested for its capacity to displace [3H]-(+)-3-PPP from guinea pig brain membranes, it exhibited a Ki of 0.34 nM, which is better than either of its parent compounds (-)-2 (Ki = 1.3 nM) and (+)-2 (Ki = 6.0 nM). Other compounds related to 3 such as N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(1-homopiperidinyl)ethy lamine (19) exhibited Ki = 0.17 nM [( 3H]-(+)-3-PPP). The determinants for high sigma receptor affinity of 3 were examined by manipulation of this structure in a number of different ways. The high efficacy of these compounds for the sigma receptor, their relative chemical simplicity and ease of synthesis, and their high degree of selective identifies N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(1-pyrrolidinyl)ethylamine (3) and related compounds as a highly promising base for determination of the functional role of sigma receptors as well as the development of novel therapeutic agents.

N-Alkyl-substituted derivatives of (+)- and (-)-cis-N-[2-(3,4-dichlorophenyl)ethyl]-2-(1-pyrrolidinyl)cyclohexylamin e have been synthesized in nine steps in a stereospecific manner starting from cyclohexene oxide. The key step in the reaction sequence involved catalytic hydrogenation of oxime 8 in the presence of PtO2 and AcOH to give the cis diamine (+/-)-7. Most of the compounds in this series exhibited very high affinity at sigma receptors when tested against [3H]-(+)-3-PPP, and in general it was observed that the 1R,2S enantiomers bound more potently to sigma receptors than their corresponding 1S,2R enantiomers. The most potent sigma ligand found in this class was the unsubstituted derivative (1R,2S)-(-)-4, which exhibited an affinity constant of 0.49 nM. This compound was also found to be very selective for sigma receptors. It exhibited little or no affinity for kappa opioid, PCP, and dopamine-D2 receptors. It was also demonstrated that the cis configuration as opposed to the trans configuration of (+)- and (-)-5 was necessary for a higher sigma receptor affinity.

Certain benzeneacetamides [(-)- and (+)-cis-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl) cyclohexyl]benzeneacetamide] were recently reported to be potent sigma receptor ligands. In order to determine whether efficacy for the sigma receptor could be improved, a series of compounds related to the benzeneacetamides, N-substituted cis-2-(1-pyrrolidinyl)-N-methylcyclohexylamines, were synthesized and their structure-activity requirements were determined. The compounds were synthesized by starting with the previously reported (+/-)-, 1S,2R-(+)-, and 1R,2S-(-)-cis-2-(1-pyrrolidinyl)-N-methylcyclohexylamines. Analysis of sigma ([3H](+)-3-PPP), kappa ([3H]bremazocine and [3H]U69,593), dopamine-d2 ([3H](-)-sulpiride), and phencyclidine (PCP) ([3H]TCP) receptor binding in guinea pig brain revealed a number of highly potent and selective sigma receptor ligands. Notably, 1S,2R-cis-(-)-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]-(2-naphthyl) acetamide [(-)-29] (Ki = 8.66 +/- 0.35 nM), (+/-)-cis-2-amino-4,5-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl] benzeneacetamide [(+/-)-17] (Ki = 11 +/- 3 nM), 1S,2R-(-)-cis-N-methyl-N-[2-(3,4-dichlorophenyl)ethyl]-2-(1-pyrrolidinyl ) cyclohexylamine [(-)-44] (Ki = 1.3 +/- 0.3 nM), and 1R,2S-(+)-cis-N-methyl-N-[2-(3,4-dichlorophenyl)ethyl]-2-(1-pyrrolidinyl ) cyclohexylamine. [(+)-44] (Ki = 6 +/- 3 nM) exhibited very high affinity at sigma receptors, by displacement of [3H]-(+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine [( 3H]-(+)-3-PPP). These compounds showed insignificant affinity for kappa, dopamine, or PCP receptors, making them valuable tools for the study of sigma receptors. Furthermore, these compounds also exhibited enantioselectivity ranging from 5-fold for (+)- and (-)-44 to 160-fold for (+)- and (-)-29. Several other compounds showed equivalent selectivity but displayed lower sigma receptor affinity.

The synthesis and in vitro sigma receptor activity of the two diastereomers of U50,488 [(+/-)-2], namely, (1R,2S)-(+)- cis-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]benzeneacet ami de [(+)-1] and (1S,2R)-(-)-cis-3,4-dichloro- N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]benzeneacetamide [(-)-1], are described. (+)-1 and (-)-1 were synthesized from (+/-)-trans-N-methyl-2-aminocyclohexanol [(+/-)-3]. Pyridinium chlorochromate (PCC) oxidation of the N-t-Boc-protected derivative of (+/-)-3 afforded (+/-)-2-[N- [(tert-butyloxy)carbonyl]-N-methylamino]cyclohexanone [(+/-)-5]. The sequence of enamine formation with pyrrolidine, catalytic reduction, N-deprotection, and optical resolution afforded (1R,2S)-(-)-cis-2-pyrrolidinyl-N-methylcyclohexylamine [(-)-10] and (1S,2R)-(+)-cis-2-pyrrolidinyl-N-methylcyclohexylamine [(+)-10]. The optical purity (greater than 99.5%) of (-)-10 and (+)-10 was determined by HPLC analysis of the diastereomeric ureas formed by reaction with optically pure (R)-alpha-methylbenzyl isocyanate. The absolute configuration of (-)-10 and (+)-10 was determined by single-crystal X-ray diffractometry of the bis-(R)-mandelate salt. Condensation of optically pure (-)-10 and (+)-10 with 3,4-dichlorophenylacetic acid furnished (+)-1 and (-)-1, respectively. Compounds (+)-1, (-)-1, (-)-2, and (+)-2 were compared for their binding affinities at kappa opioid, sigma, D2-dopamine, and phencyclidine (PCP) receptors in competitive binding assays using [3H]bremazocine ([3H]BREM) or [3H]U69,593, [3H]-(+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine [[3H]-(+)-3-PPP], or [3H]-1,3-di(o-tolyl)guanidine ([3H]DTG), [3H]-(-)-sulpiride [[3H]-(-)SULP], and [3H]-1- [1-(2-thienyl)cyclohexyl]piperidine ([3H]TCP), respectively. In the systems examined, (-)-2 exhibited the highest affinity for kappa receptors, with a Ki of 44 +/- 8 nM. However, (-)-2 also showed moderate affinity for sigma receptors, with a Ki of 594 +/- 3 nM [[3H]-(+)-3-PPP]. The (1R,2R)-(+)-enantiomer, (+)-2, had low affinity for both kappa and sigma receptors, exhibiting Ki values of 1298 +/- 49 nM at kappa ([3H]BREM) and 1270 +/- 168 nM at sigma [[3H]-(+)-3-PPP]. In contrast, the chiral cis compounds (+)-1 and (-)-1 showed high affinity for sigma receptors and negligible affinity for kappa opioid receptors in the [3H]BREM assay. Compound (-)-1 exhibited a Ki of 81 +/- 13 nM at sigma receptors [[3H]-(+)-3-PPP] and 250 +/- 8 nM ([3H]DTG).(ABSTRACT TRUNCATED AT 400 WORDS)

A series of 1-(substituted phenoxy)-3-(tert-butylamino)-2-propanols in which the ring substituents were 3,4-dihydroxy (6f), 3- and 4-hydroxy (6g and 6h, respectively), 3-hydroxy-4-methylsulfonamido (6i), its 3,4-transposed isomer (6j), and 4-methylsulfonylmethyl (6k) was prepared and examined for beta-adrenergic agonist and/or antagonist properties. Two of these compounds, 6f and 6j, were potent beta-adrenoreceptor agonists in in vitro tests that measure a compound's ability to relax guinea pig tracheal smooth muscle and to increase the rate of contraction of guinea pig right atria. Several compounds had a dose-dependent effect. Although they produced potent beta-adrenergic agonist activity at low concentrations, 6g, 6h, and 6j antagonized the effects of a standard beta-adrenoreceptor agonist at higher concentrations. The methylsulfonylmethyl derivative 6k produced beta-adrenergic blocking effects as demonstrated by attenuation of isoproterenol-induced increases in the rate of contraction of an isolated rabbit heart preparation. On the basis of these pharmacological results, coupled with NMR spectral data, it appears that the previous suggestion that aryloxypropanolamines interact with beta-adrenocreceptors as a consequence of their ability to assume an orientation in which the benzene ring the ethanolamine moieties can be superimposed on those of corresponding adrenergic phenylethanolamines is invalid. An alternative "bicyclic" rigid conformation involving two intramolecular hydrogen bonds in the protonated form of the aryloxypropanolamines is suggested to account for the similar beta-adrenoreceptor activity of these compounds and related phenylethanolamines.