Optimization of the pharmacophore model for 5-HT7R antagonism. Design and synthesis of new naphtholactam and naphthosultam derivatives

We present in this study an optimization of a preliminary pharmacophore model for 5-HT(7)R antagonism, with the incorporation of recently reported ligands and using an efficient procedure with the CATALYST program. The model consists of five features: a positive ionizable atom (PI), a H-bonding acceptor group (HBA), and three hydrophobic regions (HYD). This model has been supported by the design, synthesis, and biological evaluation of new naphtholactam and naphthosultam derivatives of general structure I (39-72). A systematic structure-affinity relationship (SAFIR) study on these analogues has allowed us to confirm that the model incorporates the essential structural features for 5-HT(7)R antagonism. In addition, computational simulation of the complex between compound 56 and a rhodopsin-based 3D model of the 5-HT(7)R transmembrane domain has permitted us to define the molecular details of the ligand-receptor interaction and gives additional support to the proposed pharmacophore model for 5-HT(7)R antagonism: (i) the HBA feature of the pharmacophore model binds Ser(5.42) and Thr(5.43), (ii) the HYD1 feature interacts with Phe(6.52), (iii) the PI feature forms an ionic interaction with Asp(3.32), and (iv) the HYD3 (AR) feature interacts with a set of aromatic residues (Phe(3.28), Tyr(7.43)). These results provide the tools for the design and synthesis of new ligands with predetermined affinities and pharmacological properties.

Design, synthesis and pharmacological evaluation of 5-hydroxytryptamine(1a) receptor ligands to explore the three-dimensional structure of the receptor

In this work, we evaluate the structural differences of transmembrane helix 3 in rhodopsin and the 5-hydroxytryptamine 1A (5-HT1A) receptor caused by their different amino acid sequence. Molecular dynamics simulations of helix 3 in the 5-HT1A receptor tends to bend toward helix 5, in sharp contrast to helix 3 in rhodopsin, which is properly located within the position observed in the crystal structure. The relocation of the central helix 3 in the helical bundle facilitates the experimentally derived interactions between the neurotransmitters and the Asp residue in helix 3 and the Ser/Thr residues in helix 5. The different amino acid sequence that forms helix 3 in rhodopsin (basically the conserved Gly(3.36)Glu(3.37) motif in the opsin family) and the 5-HT1A receptor (the conserved Cys(3.36)Thr(3.37) motif in the neurotransmitter family) produces these structural divergences. These structural differences were experimentally checked by designing and testing ligands that contain comparable functional groups but at different interatomic distance. We have estimated the position of helix 3 relative to the other helices by systematically changing the distance between the functional groups of the ligands (1 and 2) that interact with the residues in the receptor. Thus, ligand 1 optimally interacts with a model of the 5-HT1A receptor that matches rhodopsin template, whereas ligand 2 optimally interacts with a model that possesses the proposed conformation of helix 3. The lack of affinity of 1 (K(i) > 10,000 nM) and the high affinity of 2 (K(i) = 24 nM) for the 5-HT1A receptor binding sites, provide experimental support to the proposed structural divergences of helix 3 between the 5-HT1A receptor and rhodopsin.

5-HT(4) receptor antagonists: structure-affinity relationships and ligand-receptor interactions

Among serotonin receptors (5-HTRs), the 5-HT(4) subtype is of considerable interest because it is involved in (patho)physiological processes both in peripheral and central nervous systems. In addition to the clinical use of 5-HT(4R) agonists in the treatment of gastrointestinal motility disorders, the potential use of antagonists in the treatment of irritable bowel syndrome, arrhythmias and micturition disturbances are currently under investigation. This article will review the development of the most important classes of 5-HT(4R) antagonists with an emphasis on benzimidazole derivatives, their structure-affinity relationships, ligand-receptor interactions and pharmacological applications.

Arylpiperazine derivatives acting at 5-HT(1A) receptors

Serotonin (5-hydroxytryptamine, 5-HT) is one of the most attractive targets for medicinal chemists. Among 5-HTRs, the 5-HT(1A) subtype is the best studied and it is generally accepted that it is involved in psychiatric disorders such as anxiety and depression. Several structurally different compounds are known to bind 5-HT(1A)R sites. Among these, arylpiperazine derivatives represent one of the most important classes of 5-HT(1A)R ligands. This article will review the development of arylpiperazine derivatives acting at 5-HT(1A)Rs with an emphasis on structure-affinity relationships of agonists and antagonists, ligand-receptor interactions and pharmacological applications.

Biochemical, electrophysiological and neurohormonal studies with B-20991, a selective 5-HT1A receptor agonist

Different receptor subtypes mediate the effects produced by serotonin (5-HT) in mammals. Besides their proved anxiolytic action, agonists of the 5-HT1A receptor subtype show prospects as antidepressants or neuroprotective agents in case of ischemia. In order to better define the pharmacological profile and determine the selectivity for the 5-HT receptor type, the properties of the new 5-HT1A receptor agonist 2[[4-(o-methoxyphenyl)piperazin-1-yl]-methyl]-1.3-dioxoperhydroimidazo[1.5-a]pyridine (B-20991), an arylpiperazine derivative, have now been further studied. B-20991 was found to antagonize the forskolin-induced increase of cAMP synthesis in a HeLa cell line transfected with the human 5-HT1A in a process sensitive to the selective blocker N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinyl-cyclohexanecarboxamide maleate (WAY 100635). Additionally, B-20991 showed a dose-dependent inhibition of the spontaneous on-going activity of serotonin (5-HT) neurons in the dorsal raphe nucleus in rats, an effect that was reversed by treatment with WAY 100635. This, together with the fact that the hypothermia induced by B-20991 in mice was also antagonized by WAY 100635, suggests that the new compound acts upon somatodendritic 5-HT1A receptors. Additional activation of 5-HT1A postsynaptic receptors was indicated by the increase of corticosterone plasma levels induced by B-20991 in the rat. These results demonstrate that B-20991 is a selective 5-HT1A receptor agonist acting both pre- and postsynaptically, which represents an useful pharmacological tool to study 5-HT1A-receptor-mediated effects.

Synthesis and structure-activity relationships of a new model of arylpiperazines. 5. Study of the physicochemical influence of the pharmacophore on 5-HT(1a)/alpha(1)-adrenergic receptor affinity: synthesis of a new derivative with mixed 5-HT(1a)/d(2) antagonist properties

In this paper we have designed and synthesized a test series of 32 amide arylpiperazine derivatives VI in order to gain insight into the physicochemical influence of the pharmacophores of 5-HT(1A) and alpha(1)-adrenergic receptors. The training set was designed applying a fractional factorial design using six physicochemical descriptors. The amide moiety is a bicyclohydantoin or a diketopiperazine (X = -(CH(2))(3)-, -(CH(2))(4)-; m = 0, 1), the spacer length is 3 or 4 methylene units, which are the optimum values for both receptors, and the aromatic substituent R occupies the ortho- or meta-position and has been selected from a database of 387 substituents using the EDISFAR program. The 5-HT(1A) and alpha(1)-adrenergic receptor binding affinities of synthesized compounds VI (1-32) have been determined. This data set has been used to derive classical quantitative structure-activity relationships (QSAR) and neural networks models for both receptors (following paper). A comparison of these models gives information for the design of the new ligand EF-7412 (46) (5-HT(1A): K(i) = 27 nM; alpha(1): K(i) > 1000 nM). This derivative displays affinity for the dopamine D(2) receptor (K(i) = 22 nM) and is selective versus all other receptors examined (5-HT(2A), 5-HT(3), 5-HT(4) and Bz; K(i) > 1000 nM). EF-7412 (46) acts as an antagonist in vivo in pre- and postsynaptic 5-HT(1A) receptor sites and as an antagonist in the dopamine D(2) receptor. Thus, EF-7412 (46) is a derivative with mixed 5-HT(1A)/D(2) antagonist properties and this derivative could be useful as a pharmacological tool.

Synthesis and structure-activity relationships of a new model of arylpiperazines. Study of the 5-HT(1a)/alpha(1)-adrenergic receptor affinity by classical hansch analysis, artificial neural networks, and computational simulation of ligand recognition

A classical quantitative structure-activity relationship (Hansch) study and artificial neural networks (ANNs) have been applied to a training set of 32 substituted phenylpiperazines with affinity for 5-HT(1A) and alpha(1)-adrenergic receptors, to evaluate the structural requirements that are responsible for 5-HT(1A)/alpha(1) selectivity. The resulting models provide a significant correlation of electronic, steric, and hydrophobic parameters with the biological affinities. Although the derived linear Hansch correlations give good statistics and acceptable predictions, the introduction of nonlinear relationships in the analysis gives more solid models and more accurate predictions. In the ANN models on the basis of the obtained 3D plots, the 5-HT(1A) affinity has a nonlinear dependence on F, V(o), V(m), and pi(o), although the nonlinear relationship is not far from a planar one. The alpha(1)-adrenergic receptor affinity has a clear nonlinear dependence on F, V(o), V(m), pi(o), and pi(m). A comparison of both analyses gives an additional understanding for 5-HT(1A)/alpha(1) selectivity: (a) high F values increase the binding affinity for 5-HT(1A) receptors and decrease the affinity for alpha(1) sites; (b) the hydrophobicity at the meta-position has only influence for the alpha(1)-adrenergic receptor; (c) the meta-position seems to be implicated in the 5-HT(1A)/alpha(1) selectivity. While the 5-HT(1A) receptor is able to accommodate bulky substituents in the region of its active site, the steric requirements of the alpha(1)-adrenergic receptor at this position are more restricted. This information was used for the design of the new ligand EF-7412 (33) (5-HT(1A): K(i exptl) = 27 nM, alpha(1): K(i exptl) > 1000 nM; 5-HT(1A): K(i pred) (ANN) = 36 nM, alpha(1): K(i pred ANN) = 2745 nM) which was characterized as an antagonist in vivo in pre- and postsynaptic 5-HT(1A)R sites. Computational simulations of the complex between EF-7412 (33) and a 3D model of the transmembrane domain of the 5-HT(1A) receptor allowed us to define the molecular details of the ligand-receptor interaction that includes: (i) the ionic interaction between the protonated amine of the ligand and Asp 3.32; (ii) the hydrogen bonds between the m-NHSO(2)Et group of the ligand and Asn 7.39; and the hydrogen bonds between the hydantoin moiety of the ligand and (iii) Thr 3.37, (iv) Ser 5.42, and (v) Thr 5.43. These QSAR and ANN results in combination with computational simulations of ligand recognition will be useful for the design of potent selective 5-HT(1A) ligands.

First pharmacophoric hypothesis for 5-HT7 antagonism

In order to make the first contribution to the elucidation of essential structural features for 5-HT7 antagonism, a set of thirty 5-HT7 antagonists were selected from the literature. A pharmacophore model was built using Molecular Modeling studies with Catalyst program. The information contained in this model was validated with new synthesized compounds.

Benzimidazole derivatives. 2. Synthesis and structure-activity relationships of new azabicyclic benzimidazole-4-carboxylic acid derivatives with affinity for serotoninergic 5-HT(3) receptors

A new series of azabicyclic benzimidazole-4-carboxamides 2-21 and -carboxylates 22-30 were synthesized and evaluated for binding affinity at serotoninergic 5-HT(3) and 5-HT(4) receptors in the CNS. Most of the synthesized compounds exhibited high or very high affinity for the 5-HT(3) binding site and low to no significant affinity for the 5-HT(4) receptor. SAR observations indicated that a halogen atom at the 6-position and a nitro group at the 7-position of the benzimidazole ring is the best substitution pattern for 5-HT(3) affinity and 5-HT(3)/5-HT(4) selectivity, as well as no substitution in this ring. (S)-(-)-N-(Quinuclidin-3-yl)benzimidazole-4-carboxamides 2, 8, and 14 bound at central 5-HT(3) sites with high affinity (K(i) = 2.6, 0. 13, and 1.7 nM, respectively) and excellent selectivity over serotonin 5-HT(4) and 5-HT(1A) receptors (K(i) > 1000-10000 nM). Furthermore, these new 5-HT(3) receptor ligands were pharmacologically characterized as potent and selective 5-HT(3) antagonists in the isolated guinea pig ileum (pA(2) = 9.6, 9.9, and 9.1, respectively).

Benzimidazole derivatives. Part 1: Synthesis and structure-activity relationships of new benzimidazole-4-carboxamides and carboxylates as potent and selective 5-HT4 receptor antagonists

New benzimidazole-4-carboxamides 1-16 and -carboxylates 17-26 were synthesized and evaluated for binding affinity at serotonergic 5-HT4 and 5-HT3 receptors in the CNS. Most of the synthesized compounds exhibited moderate-to-very high affinity (in many cases subnanomolar) for the 5-HT4 binding site and no significant affinity for the 5-HT3 receptor. SAR observations and structural analyses (molecular modeling, INSIGHT II) indicated that the presence of a voluminous substituent in the basic nitrogen atom of the amino moiety and a distance of ca. 8.0 A from this nitrogen to the aromatic ring are of great importance for high affinity and selectivity for 5-HT4 receptors. These results confirm our recently proposed model for recognition by the 5-HT4 binding site. Amides 12-15 and esters 24 and 25 bound at central 5-HT4 sites with very high affinity (Ki = 0.11-2.9 nM) and excellent selectivity over serotonin 5-HT3, 5-HT2A, and 5-HT1A receptors (Ki > 1000-10,000 nM). Analogues 12 (Ki(5-HT4) = 0.32 nM), 13 (Ki(5-HT4) = 0.11 nM), 14 (Ki(5-HT4) = 0.29 nM) and 15 (Ki(5-HT4) = 0.54 nM) were pharmacologically characterized as selective 5-HT4 antagonists in the isolated guinea pig ileum (pA2 = 7.6, 7.9, 8.2 and 7.9, respectively), with a potency comparable to the 5-HT4 receptor antagonist RS 39604 (pA2 = 8.2). The benzimidazole-4-carboxylic acid derivatives described in this paper represent a novel class of potent and selective 5-HT4 receptor antagonists. In particular, compounds 12-15 could be interesting pharmacological tools for the understanding of the role of 5-HT4 receptors.

Design and synthesis of 2-[4-[4-(m-(ethylsulfonamido)-phenyl) piperazin-1-yl]butyl]-1,3-dioxoperhydropyrrolo[1,2-c]imidazole (EF-7412) using neural networks. A selective derivative with mixed 5-HT1A/D2 antagonist properties

A test series of 32 phenylpiperazines III with affinity for 5-HT1A and alpha1 receptors was subjected to QSAR analysis using artificial neural networks (ANNs), in order to get insight into the structural requirements that are responsible for 5-HT1A/alpha1 selectivity. Good models and predictive power were obtained for 5-HT1A and alpha1 receptors. A comparison of these models gives information for the design of the new ligand EF-7412 (5-HT1A:Ki(nM)= 27; alpha1: Ki(nM) > 1000). This derivative displayed affinity for dopamine D2 receptor (Ki = 22 nM) and is selective for all other receptor examined (5-HT2A, 5-HT3, 5-HT4 and Bz). EF-7412 acts an antagonist in vivo in pre- and postsynaptic 5-HT1A receptor sites and as an antagonist in dopamine D2 receptor.

Synthesis and structure-activity relationships of a new model of arylpiperazines. 4. 1-[omega-(4-Arylpiperazin-1-yl)alkyl]-3-(diphenylmethylene) - 2, 5-pyrrolidinediones and -3-(9H-fluoren-9-ylidene)-2, 5-pyrrolidinediones: study of the steric requirements of the terminal amide fragment on 5-HT1A affinity/selectivity

In the present paper, we report the synthesis and the binding profile on 5-HT1A, alpha1 and D2 receptors of a new series of 1-[omega-(4-arylpiperazin-1-yl)alkyl]-3-(diphenylmethylene)- 2, 5-pyrrolidinediones (III) (1-4) and -3-(9H-fluoren-9-ylidene)-2, 5-pyrrolidinediones (IV) (1-4), in which the alkyl linker contains 1-4 methylenes and the aryl group is variously substituted. The results obtained are compared to those previously reported for bicyclohydantoin (I) and the related bicyclic amine (II) series. A considerable part of the tested compounds 1-4 demonstrated moderate to high affinity for 5-HT1A and alpha1 receptor binding sites but had no affinity for D2 receptors. The study of the length of the alkyl chain and the imide substructure has allowed us to suggest some differences between the 5-HT1A and the alpha1-adrenergic receptors: (i) for III and IV, affinity for the 5-HT1A receptor as a function of the length of the methylene linker decreases in the order 4 > 1 >> 3 approximately 2, while for the alpha1 receptor affinity decreases in the order 3 approximately 4 > 1 approximately 2; (ii) the no-pharmacophoric steric pocket (receptor zone which does not hold the pharmacophore of the ligand but holds a nonessential fragment of the molecule) in the 5-HT1A receptor has less restriction than the corresponding pocket in the alpha1 receptor. Compounds 3a,e, which are highly selective for alpha1-adrenergic receptors, displayed antagonist activity. On the other hand, the best compromise between affinity and selectivity for 5-HT1A receptors is reached in these new series with n = 1, which is in agreement with our previous results for the bicyclohydantoin derivatives I. Two selected compounds (1d and 4e) retain agonist properties at postsynaptic 5-HT1A receptors. The same 5-HT1A agonist profile found in these compounds suggests the existence of two different no-pharmacophoric steric pockets in this receptor and a different interaction of compounds with n = 1 and n = 4. The information obtained from the interpretation of the energy minimization and 2D-NOESY experiments of compounds 1-4 together with the synthesis and binding data of new conformationally restrained analogues 4k-m is in good agreement with this working hypothesis.

1-[omega-(4-arylpiperazin-1-yl)alkyl]-3-diphenylmethylene-2,5- pyrrolidinediones as 5-HT1A receptor ligands: study of the steric requirements of the terminal amide fragment on 5-HT1A affinity/selectivity

In the present paper, we report the synthesis and the binding profile on 5-HT1A, alpha 1 and D2 receptors of a new series of imide-arylpiperazines 3. The study of the length of the alkyl chain and the imide substructure allows us to suggest some important differences between the no-pharmacophoric sites of both 5-HT1A and alpha 1-adrenergic receptors, which could be of great importance in order to design new selective ligands.

Preclinical pharmacology of B-20991, a 5-HT1A receptor agonist with anxiolytic activity

The purpose of this study was to characterize the pharmacological effects of 2-[[4-(o-methoxyphenyl)piperazin-1-yl]methyl]-1,3-dioxoperhydro imidazo[1,5-a]pyridine (B-20991) by using several biochemical and behavioral assays. Results of binding studies showed that B-20991 binds with high affinity to the 5-HT1A receptor (Ki = 31.7 +/- 1.7 nM), moderate affinity to 5-HT3 receptor (Ki = 269.4 +/- 23.2 nM) and low affinity (Ki > 1000) to 5-HT2A receptor, dopamine D2 receptor, benzodiazepine receptors and alpha1-adrenoceptor. The administration of B-20991 produced a dose and time related decrease in mouse rectal temperature, increased both lower lip retraction and flat body posture behavioral scores in rat, decreased 5-hydroxytryptamine (5-HT, serotonin) neuronal activity in mouse hypothalamus, and did not alter dopamine neuronal activity nor locomotor activity. The anxiolytic activity of B-20991 was assessed by using both the social interaction and light/dark box tests. The results of these tests indicated that B-20991 caused a dose-related increase in the social interaction and light/dark box behavioral scores. Taken together, these results suggest that B-20991 is a 5-HT1A receptor agonist that exhibits anxiolytic activity.

Comparative receptor mapping of serotoninergic 5-HT3 and 5-HT4 binding sites

The clinical use of currently available drugs acting at the 5-HT4 receptor has been hampered by their lack of selectivity over 5-HT3 binding sites. For this reason, there is considerable interest in the medicinal chemistry of these serotonin receptor subtypes, and significant effort has been made towards the discovery of potent and selective ligands. Computer-aided conformational analysis was used to characterize serotoninergic 5-HT3 and 5-HT4 receptor recognition. On the basis of the generally accepted model of the 5-HT3 antagonist pharmacophore, we have performed a receptor mapping of this receptor binding site, following the active analog approach (AAA) defined by Marshall. The receptor excluded volume was calculated as the union of the van der Waals density maps of nine active ligands (pKi > or = 8.9), superimposed in pharmacophoric conformations. Six inactive analogs (pKi < 7.0) were subsequently used to define the essential volume, which in its turn can be used to define the regions of steric intolerance of the 5-HT3 receptor. Five active ligands (pKi > or = 9.3) at 5-HT4 receptors were used to construct an antagonist pharmacophore for this receptor, and to determine its excluded volume by superimposition of pharmacophoric conformations. The volume defined by the superimposition of five inactive 5-HT4 receptor analogs that possess the pharmacophoric elements (pKi < or = 6.6) did not exceed the excluded volume calculated for this receptor. In this case, the inactivity may be due to the lack of positive interaction of the amino moiety with a hypothetical hydrophobic pocket, which would interact with the voluminous substituents of the basic nitrogen of active ligands. The difference between the excluded volumes of both receptors has confirmed that the main difference is indeed in the basic moiety. Thus, the 5-HT3 receptor can only accommodate small substituents in the position of the nitrogen atom, whereas the 5-HT4 receptor requires more voluminous groups. Also, the basic nitrogen is located at ca. 8.0 A from the aromatic moiety in the 5-HT4 antagonist pharmacophore, whereas this distance is ca. 7.5 A in the 5-HT3 antagonist model. The comparative mapping of both serotoninergic receptors has allowed us to confirm the three-component pharmacophore accepted for the 5-HT3 receptor, as well as to propose a steric model for the 5-HT4 receptor binding site. This study offers structural insights to aid the design of new selective ligands, and the resulting models have received some support from the synthesis of two new active and selective ligands: 24 (Ki(5-HT3) = 3.7 nM; Ki(5-HT4) > 1000 nM) and 25 (Ki(5-HT4) = 13.7 nM; Ki(5-HT3) > 10,000 nM).

Synthesis and structure-activity relationships of a new model of arylpiperazines. 3.1 2-[omega-(4-arylpiperazin-1-yl)alkyl]perhydropyrrolo- [1,2-c]imidazoles and -perhydroimidazo[1,5-a]pyridines: study of the influence of the terminal amide fragment on 5-HT1A affinity/selectivity

A series of new arylpiperazine derivatives 2, which are devoid of the terminal amide fragment present in related 5-HT1A ligands, was prepared and evaluated for affinity at 5-HT1A and alpha 1 receptors. All the compounds 2 demonstrated high affinity for the 5-HT1A receptor and moderate affinity for alpha 1 receptor binding sites. Structure-activity relationship (SAR) studies suggest that there is influence of electronic factors on the no-pharmacophoric part of the alpha 1 receptor site. However there is no influence of electronic interactions on the stabilization of the 5-HT1A receptor-ligand complex.

Synthesis and structure-activity relationships of a new model of arylpiperazines. 2. Three-dimensional quantitative structure-activity relationships of hydantoin-phenylpiperazine derivatives with affinity for 5-HT1A and alpha 1 receptors. A comparison of CoMFA models

A series of 48 bicyclohydantoin-phenylpiperazines (1-4) with affinity for 5-HT1A and alpha 1 receptors was subjected to three-dimensional quantitative structure-affinity relationship analysis using comparative molecular field analysis (CoMFA), in order to get insight into the structural requirements that are responsible for 5-HT1A/alpha 1 selectivity. Good models (high cross-validation correlations and predictive power) were obtained for 5-HT1A and alpha 1 receptors. The resulting 3D-QSAR models rationalize steric and electrostatic factors which modulate binding to 5-HT1A and alpha 1 receptors. A comparison of these models gives an additional understanding for 5-HT1A/alpha 1 selectivity: (a) Substitution at the ortho position by a group with negative potential is favorable to affinity for both receptors. (b) The meta position seems to be implicated in 5-HT1A/alpha 1 selectivity. While the 5-HT1A receptor is able to accommodate bulky substituents in the region of its active site, the steric requirements of the alpha 1 receptor are more restricted (optimum volume of substituent 11-25 A3). (c) For both receptors the para position represents a region where the volume accessible by the ligands is limited. (d) The hydantoin moiety and the side chain length seem to modulate not only the affinity but also 5-HT1A/alpha 1 selectivity. The 3D-QSAR models reveal an useful predictive information for the design of new selective ligands.

Synthesis and structure-activity relationships of a new model of arylpiperazines. 1. 2-[[4-(o-methoxyphenyl)piperazin-1-yl]methyl]-1, 3-dioxoperhydroimidazo[1,5-alpha]pyridine: a selective 5-HT1A receptor agonist

A series of new bicyclohydantoin-arylpiperazines was prepared and evaluated for affinity at 5-HT1A, alpha 1, and D2 receptors. Most of the compounds showed very low affinity for D2 receptors, and most of them demonstrated moderate to high affinity for 5-HT1A and alpha 1 receptor binding sites. SAR observations indicated that the length of the alkyl chain between the arylpiperazine and the hydantoin moiety is of great importance for 5-HT1A/alpha 1 affinity and selectivity, n = 1 being the optimal value. Compound 1h, 2-[[4-(o-methoxyphenyl)piperazin-1-yl] methyl]-1,3-dioxoperhydroimidazo [1,5-alpha]pyridine, bound at 5-HT1A sites with nanomolar affinity (Ki = 31.7 nM) and high selectivity over alpha 1, D2, and 5-HT2A receptors (Ki > 1000, > 10 000, and > 1000 nM, respectively). Preliminary studies showed that this agent is probably functioning as a partial to full 5-HT1A agonist, and it displayed anxiolytic activity on the social interaction test in mice.

Alpha 1-adrenoceptor reagents. Synthesis of some 5,6,11,11a-tetrahydro-1H-imidazo[1',5':1,6]pyrido and 5,6,11,11b-tetrahydro-1H-imidazo[1',5':1,2]pyrido[3,4-b]indole-1,3(2H) -diones

Several 2-substituted 5,6,11,11a-tetrahydro-1H-imidazo[1',5':1,6]pyrido (1) and 5,6,11,11b-tetrahydro-1H-imidazo [1',5':1,2]pyrido[3,4-b]indole,3(2H)-diones (2) were synthesized and studied by 2D-NMR spectroscopy and difference nuclear Overhauser effect experiments. All the compounds were evaluated for in vitro alpha(1) adrenoceptor affinity by radioligand receptor binding assays. The most active derivative in displacement of [3H]prazosin from rat cortical membranes was 1b (K(i) = 219 nM). At 1 microM concentration, compounds 1 and 2 had no effect on the benzodiazepine or 5-HT(1A) receptor. The biological activity profile of 1b makes it a possible lead compound for the design of new selective alpha1 adrenoceptor ligands.

Reaction of 6-hydroxytetrahydro-beta-carboline-3-carboxylic acids with isocyanates and isothiocyanates

The reaction of (-)-(3,S)-6-hydroxy-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid (3a) with isocyanates and isothiocyanates gave the (+/-)-beta-carboline-hydantoin (4a-d) and -thiohydantoin systems (5a-d). The treatment of (-)-(1S,3S)-6-hydroxy-1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-ca rbo xylic acid (3b) with isocyanates yielded the (+/-)-cis diastereomer of the beta-carboline-hydantoin rings (4e-h). However, the reaction of 3b with isothiocyanates provided the corresponding trans isomer (5e-h). These results have been confirmed by 13C-NMR data and nuclear Overhauser effect (NOE) experiments. The new compounds were tested for in vitro binding affinity to the central-type benzodiazepine receptors.

Synthesis, structure and cytostatic activity of a series of N-substituted 3,4-diphenyl-1H-pyrrole-2,5-diones

A series of N-substituted 3,4-diphenyl-1H-pyrrole-2,5-diones (diphenylmaleimides) (IV) were synthesized and tested for cytostatic activity. Compounds IVa--k were prepared from diphenylmaleic anhydride or its dinitro derivative (V or VI) and the corresponding amine. Compounds IVl--n were obtained by reaction of 3-(p-nitrophenyl)-4-phenyl-1H-pyrrole-2,5-dione potassium salt with the appropriate chloroalkylamine. Hydrogenation of IVl,n gave the the corresponding cis-3-(p-aminophenyl)-4-phenylsuccinimides (VIIIa,b). The structure-cytostatic activity relationship of these compounds is discussed.