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Structure−affinity relationships of N-[4-(4-arylpiperazin-1-yl)butyl]arylcarboxamides as D3 receptor ligands have been well characterized but not structure−activity relationships. In a first attempt to clarify this issue, seven 1-(2,3-dichlorophenyl)piperazine derivatives and their 2-methoxyphenyl counterparts were prepared by varying the arylcarboxamide moiety. They were tested for D3 receptor binding affinities and in the Eu-GTP binding assay in order to evaluate their intrinsic activity. We have found that the intrinsic activity strongly depended on the nature of the arylcarboxamide moiety.

The selective dopamine D3 receptor ligands N-4-[4-[(2,3-dichlorophenyl)piperazin-1-yl]butyl]1-methoxy-2-naphthalencarboxamide (1) and N-4-[4-[(2,3-dichlorophenyl)piperazin-1-yl]butyl]-7-methoxy-2-benzofurancarboxamide (2) were labeled with ¹¹C (t1/2 = 20.4 min) as potential radioligands for the noninvasive assessment of the dopamine D3 neurotransmission system in vivo with positron emission tomography (PET). The radiosynthesis consisted in an O-methylation of the des-methyl precursors N-[4-[4-(2,3-dichlorophenyl)piperazin-1-yl]butyl]-1-hydroxy-2-naphthalenecarboxamide (3) and N-[4-[4-(2,3-dichlorophenyl)piperazin-1-yl]butyl]-7-hydroxy-2-benzofurancarboxamide (4) with [¹¹C]methyl iodide using tBuOK/HMPA and KOH/DMSO, respectively. The radiotracers [¹¹C]1 and [¹¹C]2 were obtained in 35 min with over 99% radiochemical purity, 74 ± 37 GBq/μmol of specific radioactivity, 13% and 26% radiochemical yield (EOB, decay-corrected). Distribution studies in rats demonstrated that the new tracers [¹¹C]1 and [¹¹C]2 cross the blood−brain barrier and localize in the brain. However, the kinetics of cerebral uptake did not reflect the regional expression of the D3 receptors. Despite their in vitro pharmacological profile, [¹¹C]1 and [¹¹C]2 do not display an in vivo behavior suitable to image D3 receptor expression using PET.

A series of N-(1,2,3,4-tetrahydronaphthalen-1-yl)-4-aryl-1-piperazinealkylamides was prepared and their affinity for serotonin (5-hydroxytryptamine, 5-HT) 5-HT7, 5-HT1A, and 5-HT2A receptors was measured by in vitro binding assays. In relation to 5-HT7 receptor affinity, receptor binding studies indicated that (i) the optimal alkyl chain length was five methylenes, (ii) an unsubstituted 1,2,3,4-tetrahydronaphthalenyl nucleus was preferred, and (iii) the substitution pattern of the aryl ring linked to the piperazine ring played a crucial role. Several compound with high affinity for 5-HT7 receptors were identified. Among them, 4-(2-methoxyphenyl)-N-(1,2,3,4-tetrahydronaphthalen-1-yl)-1-piperazinehexanamide (28), 4-(2-acetylphenyl)-N-(1,2,3,4-tetrahydronaphthalen-1-yl)-1-piperazinehexanamide (34), 4-(2-methylthiophenyl)-N-(1,2,3,4-tetrahydronaphthalen-1-yl)-1-piperazinehexanamide (44), 4-(2-hydroxyphenyl)-N-(1,2,3,4-tetrahydronaphthalen-1-yl)-1-piperazinehexanamide (46), and 4-(2-methylphenyl)-N-(1,2,3,4-tetrahydronaphthalen-1-yl)-1-piperazinehexanamide (49) were assayed for the 5-HT7 receptor-mediated relaxation of substance P-induced guinea pig ileum contraction. Compounds 28, 44, and 49 behaved as full agonists and compound 34 as a partial agonist, whereas derivative 46 acted as an antagonist. Among the compounds presented here, it emerged that 44 was identified as a potent 5-HT7 receptor agonist (Ki = 0.22 nM, EC50 = 2.56 μM), endowed with selectivity over 5-HT1A and 5-HT2A receptors (200-fold and >1000-fold, respectively).

Several 1-cyclohexylpiperazine derivatives related to σ2 receptor ligand 1-cyclohexyl-4-[3-(5-methoxy-1,2,3,4-tetrahydronaphthalen-1-yl)propyl]piperazine (33, Ki = 0.34 nM) were synthesized and tested in radioligand binding assays, to attempt a structure−affinity relationship study. Intermediate alkyl chain length and methoxyl group position on the tetralin nucleus were varied. A few naphthalene analogues were also prepared. High affinities were found in σ2 receptor binding for almost all compounds, some of which displayed Ki values in subnanomolar range, but low σ2/σ1 selectivities were found. The highest σ2 affinities were displayed by compounds with an intermediate alkyl chain of three (32 and 43) or five methylenes (39 and 46). Quite high σ1 receptor affinity was found for compounds with a four-methylene chain; 36 (Ki = 0.036 nM) and 45 (Ki = 0.22 nM) displaying good σ1/σ2 selectivity (406- and 139-fold, respectively). Moreover, homologues of compound 33 displayed also satisfactory selectivities over dopamine D2-like, serotonin 5-HT3, and adrenergic α1 receptors. These compounds and a few others were tested in the inhibition of the electrically evoked contractions in guinea pig bladder and were demonstrated to be full σ2 agonists. The activity values correlated well to the affinity scale (EC50 in μM range). 33 and related compounds are proposed as a class of potential antineoplastic and PET diagnosis agents.

Sumitomo's patented σ ligand 1-[3-(4-chlorophenoxy)propyl]-4-methylpiperidine (15), which has been claimed as agent for CNS disorders and neuropathies, and its lower homologue 12 were prepared along with related chiral (4-chlorophenoxy)alkylpiperidines. They were tested at σ1, σ2, and sterol Δ8−Δ7 isomerase (SI) sites by in vitro radioligand binding assays, to evaluate the influence of a chiral center in the alkyl chain on the selective σ1 binding relative to other σ family sites. Generally high σ1-site affinities were found, so that the chirality introduced by a methyl substitution resulted in slight differences. Nevertheless, the shorter oxyethylenic chain was beneficial to increase σ1 selectivity. However, the (−)-(S)-4-methyl-1-[2-(4-chlorophenoxy)-1-methylethyl]piperidine ((−)-(S)-17) reached the highest σ1 affinity (Ki = 0.34 nM) and the best selectivity relative to the σ2 site (547-fold). Compound (−)-(S)-17 displayed also a moderate selectivity (11-fold) relative to the SI site.

Structural requirements for 5-HT7 receptor affinity and selectivity over that for the 5-HT1A receptor were studied on a series of 1-[ω-(4-aryl-1-piperazinyl)alkyl]-1-aryl ketones. The presence of a hydroxy or methoxy substituent on aryl ketone moiety, alkyl chain length, and the nature of N-1-piperazine substituent were explored. 6-[4-(3-Benzisoxazolyl)-1-piperazinyl]-1-(2-hydroxyphenyl)-1-hexanone (40) and its methoxy analogue 43 exhibited high 5-HT7 receptor affinities (Ki = 2.93 nM and 0.90 nM, respectively) and agonist properties when tested for 5-HT7 receptor-mediated relaxation of substance P-induced guinea-pig ileum contraction.

The benzamide PB12 (N-[2-[4-(4-chlorophenyl)piperazin-1-yl]ethyl]-3-methoxybenzamide) (1), already reported as potent and selective dopamine D4 receptor ligand, has been modified searching for structural features that could lead to D3 receptor affinity. Changes in the aromatic ring linked to N-1 piperazine ring led to the identification of 2-methoxyphenyl and 2,3-dichlorophenyl derivatives (compounds 6 and 13) displaying moderate D3 affinity (Ki = 145 and 31 nM, respectively). Intermediate alkyl chain elongation in compounds 1, 6, and 13 improved binding affinity for the D3 receptor and decreased the D4 affinity (compounds 18−26). Among these latter compounds, the N-[4-[4-(2,3-dichlorophenyl)piperazin-1-yl]butyl]-3-methoxybenzamide (19) was further modified with the replacement or of the 2,3-dichlorophenyl moiety (compounds 27−30) or of the 3-methoxyphenyl ring (compounds 31−41). In this way, we identified several high-affinity D3 ligands (0.13 nM < Ki's < 4.97 nM) endowed with high selectivity over D2, D4, 5-HT1A, and α1 receptors. In addition, N-[4-[4-(2,3-dimethylphenyl)piperazin-1-yl]butyl]-3-methoxybenzamide (27) and N-[4-[4-(2,3-dichlorophenyl)piperazin-1-yl]butyl]-7-methoxy-2-benzofurancarboxamide (41) appear to be valuable candidates for positron emission tomography (PET) because of their affinity values, lipophilicity properties, and liability of ¹¹C labeling in the O-methyl position.

The present paper concerns the influence of conformational parameters on the recognition by rat 5-HT1A receptors of derivatives 4-[3-(5-methoxy-1,2,3,4-tetrahydronaphthalen-1-yl)propyl]-1-(2-pyridinyl)piperazine (1a) and 3-(5-methoxy-1,2,3,4-tetrahydronaphthalen-1-yl)-N-[2-(2-pyridyloxy)ethyl]propanamine (3b), two highly potent and selective 5-HT1A receptor ligands. Fifteen corresponding flexible and rigid analogues were prepared following several synthetic routes and were tested in binding assays with radioligands at 5-HT1A, D2, and α1 receptors from rat brain membranes. Among the new derivatives emerged trans-4-[4-(3-methoxyphenyl)cyclohexyl]-1-(2-pyridinyl)piperazine (trans-8a) and trans-N-[4-(3-methoxyphenyl)cyclohexyl]-2-(2-pyridyloxy)ethylamine (trans-8b). These compounds can be considered as conformationally constrained analogues of compounds 1a and 3a, respectively. In fact, compounds trans-8a and trans-8b showed a marked enhancement in 5-HT1A receptor affinity when compared to the corresponding cis isomers. Because compound trans-8a was a potent and selective 5-HT1A ligand (Ki, nM:  5-HT1A = 0.028, D2 = 2194, α1 = 767), it was chosen as a lead to prepare other analogues that were tested at 5-HT1A, D2, and α1 receptors from rat brain membranes, showing high affinity at the 5-HT1A and selectivity vs D2 and α1 receptors. Selected compounds were tested for their affinity at the human cloned 5-HT1A, α1a, α1b, α1d receptor subtypes. They were also submitted to the [³⁵S]GTPγS binding assay stimulating the 5-HT1A receptor-mediated G-protein activation, therefore behaving as full or as partial agonists. Finally, the ability of iv administration of trans-8a to induce fore-paw treading in rats was evaluated in comparison with 8-OH-DPAT. Although the affinity (Ki) and in vitro activity (pD‘2) of trans-8a at the 5-HT1A receptor were higher than those of 8-OH-DPAT, the compound was less potent than the reference standard in inducing the symptom.

N-[2-[4-(4-Chlorophenyl)piperazin-1-yl]ethyl]-3-methoxybenzamide (1), a high-affinity and selective dopamine D4 receptor ligand, was chosen as a lead, and structural modifications were done on its amide bond and on its alkyl chain linking the benzamide moiety to the piperazine ring and by preparing some semirigid analogues. The binding profile at dopamine D4 and dopamine D2, serotonin 5-HT1A, and adrenergic α1 receptors of 16 new compounds was determined. From the results emerged that the modification of the amide bond and the elongation of the intermediate alkyl chain caused a decrease in dopamine D4 receptor affinity. All prepared semirigid analogues displayed D4 receptor affinity values in the same range of the opened counterparts.

Some 1-aryl-4-[(5-methoxy-1,2,3,4-tetrahydronaphthalen-1-yl)-n-propyl]piperazines and their alkylamino and alkylamido analogues, previously studied as 5-HT1A ligands, were prepared in enantiomerically pure form, and their absolute configuration was determined by chemical correlation or by chiroptical properties. They were evaluated for in vitro 5-HT1A, D2, and α1 receptor affinity by radioligand binding assays, to study the influence of the chiral carbon atom of the tetrahydronaphthalene nucleus on the 5-HT1A affinity and selectivity. Results indicated that, as regarding the 5-HT1A receptor affinity, there was no difference in affinity between (−)- and (+)-enantiomers as well as the racemate of each compound. The stereochemistry, instead, influenced the selectivity:  all (−)-enantiomers displayed affinity values higher than those of (+)-isomers at D2 receptors, and conversely, all (+)-enantiomers displayed affinity values higher than those of (−)-isomers at α1 receptors. As a result of this trend, it is not possible to predict the isomer with a better selectivity profile. However, compounds (S)-(+)-2, (S)-(+)-4, and (R)-(+)-6 displayed high affinity for the 5-HT1A receptor (IC50 values ranging between 7.0 and 2.3 nM) and good selectivity (≥250-fold) versus both D2 and α1 receptors. Furthermore, compounds (S)-(+)-4 and (R)-(−)-4 were submitted to the [³⁵S]GTPγS binding assay for a preliminary evaluation of their intrinsic activity on the 5-HT1A receptor.

The synthesis of 1-phenylpiperazines, linked in the α or β position of the tetralin moiety on the terminal part of the N-4 alkyl chain, and their radioligand binding affinities for 5-HT1A, 5-HT2A, D-1, D-2, α1, and α2 receptors along with SAR studies on the 5-HT1A receptor are reported. Several changes have been carried out on previous structures of type 2, by inserting the alkyl chain with variable length in the α or β position of the tetralin moiety and by changing the position of the methoxy group on the aromatic ring of the tetralin nucleus. The highest affinity (IC50 = 0.50 nM) and selectivity for the 5-HT1A receptor were showed by 1-phenylpiperazine 2a with a three-membered alkyl chain bearing a 5-methoxytetralin-1-yl ring in the ω position.

A series of substituted N-[(tetralin-1-yl)alkyl]piperidines and a number of related N-di-n-propyl[(tetralin-1-yl)alkyl]amines were prepared. Structural modifications such as piperidine substitutions, intermediate chain lengthening, and the nature of the aromatic ring were explored in order to identify structural requirements for selective σ1 affinity. They were tested in radioligand binding assays on σ1, 5-HT1A and 5-HT2 serotonergic, PCP (phencyclidine), and D-2 dopaminergic receptors. Almost all the compounds reported here showed a high to superpotent σ1 affinity, and some compounds also demonstrated a widespread selectivity over the other receptors. In [³H]-(+)-pentazocine binding, 3,3-dimethyl-1-[3-(5-methoxy-1,2,3,4-tetrahydronaphthalen-1-yl)-n-propyl]piperidine (24) and 3,3-dimethyl-1-[4-(1,2,3,4-tetrahydronaphthalen-1-yl)-n-butyl]piperidine (26) reached the lowest Ki values (0.4 and 0.8 nM, respectively); compound 24 also demonstrated a considerable PCP affinity (Ki = 34.2 nM), whereas compound 26 was suitably selective. Furthermore the presence of a 4-benzyl substituent on the piperidine ring (compound 16, Ki = 3.9 nM on σ1 sites) caused an increase in 5-HT1A affinity (Ki < 0.14 nM).

The synthesis and binding profile on 5-HT1A, 5-HT2, D-1, D-2, α1, and α2 receptors of the N-4 long-chain arylpiperazines 22−40 are reported, where an amino or amido function is inserted into the intermediate chain linked to the α position of the tetralin nucleus. Unlike the buspirone analogues, for the amido derivatives studied in this paper, the terminal amide function of long-chain piperazines is not important for 5-HT1A receptor affinity binding, and its removal yields high-affinity 5-HT1A receptor agents.

A series of new 1-aryl-4-alkylpiperazines containing a terminal benzamide fragment or a tetralin-1-yl nucleus on the alkyl chain were synthesized and tested for binding at cloned human dopamine D4 and D2 receptor subtypes. A SAFIR (structure−affinity relationship) study on this series is herein discussed. The most relevant D4 receptor affinities were displayed by N-[ω-[4-arylpiperazin-1-yl]alkyl]-methoxybenzamides (compounds 5, 16−20), their IC50 values ranging between 0.057 and 7.8 nM. Among these, N-[2-[4-(4-chlorophenyl)piperazin-1-yl]ethyl]-3-methoxybenzamide (17) emerged since it exhibited very high affinity for dopamine D4 receptor (IC50 = 0.057 nM) with selectivity of >10 000 for the D4 versus the D2 receptor; compound 17 was also selective versus serotonin 5-HT1A and adrenergic α1 receptors.

Several 3,3-dimethyl-N-[ω-(tetrahydronaphthalen-1-yl)alkyl]piperidine derivatives and some related compounds were prepared. Their affinities and σ-subtype selectivities were investigated by radioligand binding assays, labeling σ1 receptors with [³H]-SKF 10047 and σ2 receptors with [³H]-DTG. Many tested compounds bound σ1 and/or σ2 receptors with nanomolar or subnanomolar IC50 values. Compound (+)-22, (+)-3,3-dimethyl-1-[3-(5-methoxy-1,2,3,4-tetrahydronaphthalen-1-yl)-n-propyl]piperidine, was the most potent (IC50 = 0.089 nM) and selective σ1 ligand (1340-fold), showing a 10-fold enantioselectivity. Compounds 29 (3,3-dimethyl-1-[4-(6-methoxy-1,2,3,4-tetrahydronaphthalen-1-yl)-n-butyl]piperidine) and 31 (3,3-dimethyl-1-[5-(1,2,3,4-tetrahydronaphthalen-1-yl)-n-pentyl]piperidine) were highly potent (IC50 = 0.016 nM and IC50 = 0.008 nM, respectively) and highly selective σ2 ligands (more than 100 000-fold).

Two series of compounds that are structurally related to benzomorphans, derived by structural modification of arylpiperazines with high 5-HT1A affinity and moderate σ affinity, were prepared in order to increase σ affinity and selectivity. All new compounds are N-substituted-ω-(1,2,3,4-tetrahydronaphthalen-1-yl)- or -ω-(1,2-dihydronaphthalen-4-yl)-n-alkylamines with, in some cases, a methoxy group on the tetralin moiety. They were tested in radioligand binding assays on σ ([³H]DTG and [³H]-(+)-pentazocine), D-2 dopaminergic, 5-HT1A and 5-HT2 serotonergic, and PCP (phencyclidine) receptors. A first set of compounds bearing a 4-(1-substituted)piperazine moiety as terminal fragment on the alkyl chain showed moderate to high σ affinity (Ki = 5.3−139 nM), the most active and selective being 1-cyclohexyl-4-[3-(5-methoxy-1,2,3,4-tetrahydronaphthalen-1-yl)-n-propyl]piperazine (14), with probable pronounced σ2 affinity (Ki = 5.3 nM on [³H]DTG and Ki = 71 nM on [³H]-(+)-pentazocine). Moreover, compound 13, a 1-benzylpiperazine analogue of 14, preserved a dual high 5-HT1A and σ affinity (Ki = 3.6 nM on [³H]-5-HT and Ki = 7.0 nM on [³H]DTG). The second set of compounds includes some N-phenylalkyl derivatives of 3-(5-methoxy-1,2,3,4-tetrahydronaphthalen-1-yl)-n-propylamine that can be considered to be open-chain derivatives of 4-substituted-1-arylpiperazines. Among these compounds that had a lower activity toward σ binding sites, a high 5-HT1A affinity was found for the N-(3-phenylpropyl) derivative 21 (Ki = 4.4 nM) which demonstrated very good selectivity.

A total of 1095 patients with operable breast cancer and en-rolled in a randomized clinical trial were analysed for estrogen (ER) and progesterone (PgR) receptor content of their primary tumor, and the relationships between steroid receptor status and several epidemiologic characteristics were studied. The proportion of ER+ and median ER levels increased with age: compared to women younger than 40, those aged 66 or more were approximately three times more likely to have an ER+ tumor (OR = 3.0, 95% C.I. = 1.6–5.7). This difference tended to be more marked after comparison between patients with ER > 100 fmol/mg protein and ER- within the same age groups: OR = 7.04, 95 % C.I. = 2.89–17.12. No association emerged between age and PgR. ER status and concentrations were independent of menopausal status after adjustment for age, whereas the proportion of PgR+ and PgR levels were significantly lower in postmenopausal patients of the same age. The distribution of ER and PgR profiles was similar in relation to family history of breast cancer, reproductive events and other selected epidemiologic characteristics of the patients.