Central Benzodiazepine Receptors Research Articles

Structure–activity relationship of wedelolactone analogues: Structural requirements for inhibition of Na+,K+-ATPase and binding to the central benzodiazepine receptor

Coumestans 2a–i, bearing different patterns of substitution in A- and D-rings, were synthesized and evaluated as inhibitors of kidney Na+,K+-ATPase and ligands for the central benzodiazepine (BZP) receptor. The presence of a hydroxyl group in position 2 favours the effect on Na+,K+-ATPase but decreases the affinity for the BZP receptor, allowing the design of more selective molecules than the natural wedelolactone. On the other hand, the presence of a catechol in ring D is important for the effect on both molecular targets.

Interaction of Novel Condensed Triazine Derivatives with Central and Peripheral Type Benzodiazepine Receptors: Synthesis, in vitro Pharmacology and Modelling.

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Diazepam Enhances Inotropic Responses to Dopamine in Rat Ventricular Myocardium

Diazepam inhibits phosphodiesterase type 4 and enhances the effect of some 3',5'-cyclic adenosine monophosphate (cAMP)-dependent positive inotropic drugs. We sought to determine whether diazepam and the selective phosphodiesterase type 4 inhibitor rolipram enhances the contractile response and cAMP levels induced by dopamine in rat myocardium. Dopamine (3-100 microM) produced concentration-dependent positive inotropic effects (-log EC50 = 5.21 +/- 0.2, n = 5), which were augmented in the presence of 10 microM diazepam (-log EC50 = 5.40 +/- 0.08, n = 6, P < 0.05) or 1 microM rolipram (-log EC50 = 5.41 +/- 0.1, n = 6, P < 0.05). The effect of diazepam was not mimicked by 100 microM gamma-aminobutyric acid nor it was antagonized by a 5 microM concentration of the blockers of central and peripheral type benzodiazepine receptors, flumazenil and PK 11195. cAMP levels (pmol/g) produced by dopamine (744.4 +/- 111.8, n = 5) in this tissue were enhanced by the presence of diazepam (1073 +/- 97.7, n = 6, P < 0.05) or rolipram (1034.0 +/- 245.2, n = 5, P < 0.05). Therefore, diazepam, like rolipram, augments the inotropic and biochemical effects of dopamine in rat myocardium. This effect is not mediated by benzodiazepine receptors but is probably the consequence of the phosphodiesterase type 4 inhibitory activity of diazepam.

Synthesis and in vitro binding of N, N-dialkyl-2-phenylindol-3-yl-glyoxylamides for the peripheral benzodiazepine binding sites

A series of N, N-dialkyl-2-phenylindol-3-ylglyoxylamides bearing the halogens iodine and bromine were synthesised and their binding affinity for the peripheral benzodiazepine binding sites (PBBS) in rat kidney mitochondrial membranes was evaluated using [ 3H]PK11195. Central benzodiazepine receptor (CBR) affinities were also evaluated in rat cortices using [ 3H]flumazenil to determine their selectivity for PBBS over CBR. The tested compounds had PBBS binding affinities (IC 50) ranging from 7.86 to 618 nM, with all compounds showing high selectivity over the CBR (CBR IC 50 > 5000 nM). Among the 12 compounds tested, those with a diethylamide group were the most potent. The highest affinity iodinated PBBS ligand, N, N-diethyl-[5-chloro-2-(4-iodophenyl)indol-3-yl]glyoxylamide ( 4c), was radiolabelled with iodine-123. This high affinity and selective radioligand may be useful for imaging neurodegeneration, inflammation and tumours using single photon emission computed tomography.

Central and Peripheral Benzodiazepine Receptors

Central and Peripheral Benzodiazepine Receptors

Use of the pig caecum model to mimic the human intestinal metabolism of hispidulin and related compounds

Up to now, the metabolism of hispidulin (5,7,4'-trihydroxy-6-methoxyflavone), a potent ligand of the central human benzodiazepine receptor, has not been investigated. To elucidate the metabolism of hispidulin in the large intestine, its biotransformation by the pig caecal microflora was studied. In addition, the efficiency of the pig caecal microflora to degrade galangin (3,5,7-trihydroxyflavone), kaempferol (3,5,7,4'-tetrahydroxyflavone), apigenin (5,7,4'-trihydroxyflavone), and luteolin (5,7,3',4'-tetrahydroxyflavone) was investigated. Identification of the formed metabolites was performed by high-performance liquid chromatography (HPLC)-diode array detection, HPLC-electrospray ionization-tandem mass spectrometry, and high-resolution gas chromatography-mass spectrometry. The caecal microflora transformed hispidulin to scutellarein (5,6,7,4'-tetrahydroxyflavone), an effective alpha-glucosidase inhibitor, and 3-(4-hydroxyphenyl)-propionic acid; galangin to phenylacetic acid and phloroglucinol; kaempferol to 4-hydroxyphenylacetic acid, phloroglucinol, and 4-methylphenol; apigenin to 3-(4-hydroxyphenyl)-propionic acid and 3-phenylpropionic acid, and luteolin to 3-(3-hydroxyphenyl)-propionic acid, respectively. To elucidate to what extent different hydroxylation patterns on the B-ring influence the degradation degree of flavonoids, the conversions of galangin and kaempferol as well as that of apigenin and luteolin were compared with those of quercetin (3,5,7,3',4'-pentahydroxyflavone) and chrysin (5,7-dihydroxyflavone), respectively. Regardless of the flavonoid subclass, the presence of a hydroxy group at the 4'-position seems to be a prerequisite for fast breakdown. An additional hydroxy group at the B-ring did not affect the degradation degree.

EPILEPSY SURGERY FOR NEONATAL OR INFANTILE ONSET SEIZURES: USE OF PET SCANNING

Intractable epilepsy in infants and young children may lead to an epileptic encephalopathy. In such cases, epilepsy surgery should be considered. Surgical results are best when there is concordance between EEG localization and neuroimaging. PET scanning using 2-deoxy-2(18F)fluoro-D-glucose (FDG) identifies epileptic foci when MRI is non-revealing, and when a lesion is present, PET complements MRI by defining the full extent of the lesion and evaluating the integrity of surrounding brain regions. PET abnormalities may guide placement of intracranial electrodes, thus minimizing sampling errors. The size of the hypometabolic zone increases with chronic epilepsy, suggesting dynamic changes in the epileptic network. In infantile spasms, resection of focal PET abnormalities corresponding to focal EEG abnormalities is associated with improved seizure/cognitive outcome. Only about 20% of patients with 'cryptogenic infantile spasms' show a single PET focus amenable to resection. The majority shows multifocal hypometabolism and are not optimal surgical candidates. Bilateral symmetric hypometabolism suggests a nonlesional etiology, more consistent with neurogenetic/neurometabolic disorders. In infants with hemimegalencephaly, the relative integrity of the contralateral hemisphere is assessed using PET for prognostic purposes. In patients with Sturge-Weber syndrome, rapid demise of the affected hemisphere is associated with better seizure/cognitive outcome than slower progression because of brain plasticity. Other PET tracers may provide more specific assessment of seizure foci. 11C-flumazenil (FMZ) labels central benzodiazepine receptors, showing: decreased receptor binding in medial temporal sclerosis, perilesional epileptogenic zones, seizure onset zones, and secondary epileptic foci. 11C-alpha-methyl-L-tryptophan (AMT), an analogue of tryptophan, traces serotonin synthesis and kynurenine pathways and shows increased uptake in epileptogenic cortex interictally. In children with tuberous sclerosis, increased AMT uptake is seen around epileptogenic tubers, but not nonepileptogenic tubers. The list of PET tracers for epilepsy continues to grow and will eventually pinpoint precisely the cortical regions that should be resected to achieve best postoperative outcome.

On the mechanism of anticonvulsant effect of tramadol in mice

The present study was conducted to examine the effects of tramadol, an atypical opioid on convulsive behaviour in maximal electroshock (MES) seizure test on mice. Moreover, an attempt was also made to investigate the role of possible receptor mechanisms involved. MES seizures were induced via transauricular electrodes (60 mA, 0.2 sec). Seizure severity was determined by (1) the duration of tonic hindlimb extensor (THE) phase and by (2) mortality due to electroconvulsions. Intraperitoneal (i.p.) administration of tramadol dose-dependently (10–50 mg/kg) decreased the duration of THE phase of MES. The anticonvulsant effect of tramadol was antagonized by the opioid antagonists, naloxone in high dose, and MR2266, a selective kappa antagonist but not by naltrindole, a delta opioid antagonist. Coadministration of either γ-aminobutyric acid (GABA)-ergic drugs (diazepam, GABA, muscimol and baclofen) or N-methyl- d-aspartate (NMDA) receptor antagonist, MK801 with tramadol augmented the anticonvulsant effect of the latter drug. By contrast, flumazenil, a central benzodiazepine (BZD) receptor antagonist, counteracted the diazepam-induced facilitation of anti-MES effect of tramadol. Similarly, δ-aminovaleric acid (DAVA), a GABA B receptor antagonist, abolished the facilitatory effect of baclofen, a GABA B agonist on anti-MES action of tramadol. These BZD–GABAergic antagonists, flumazenil or DAVA, on their own also antagonized the anti-MES effect of tramadol administered alone. No significant effect on mortality was observed in any of the studied groups. Taken together, the current results have demonstrated a possible role for multitude of important neurotransmitter systems, i.e., opioid (kappa), GABA A–BZD receptors system, GABA B receptors and NMDA channel involvement in the antielectroshock effect of tramadol in mice.

Synthesis and in vivo evaluation of a novel peripheral benzodiazepine receptor PET radioligand

The novel pyrazolopyrimidine ligand, N, N-diethyl-2-[2-(4-methoxyphenyl)-5,7-dimethyl-pyrazolo[1,5- a]pyrimidin-3-yl]-acetamide 1 (DPA-713), has been reported as a potent ligand for the peripheral benzodiazepine receptor (PBR) displaying an affinity of K i = 4.7 nM. In this study, 1 was successfully synthesised and demethylated to form the phenolic derivative 6 as precursor for labelling with carbon-11 ( t 1/2 = 20.4 min). [ 11C] 1 was prepared by O-alkylation of 6 with [ 11C]methyl iodide. The radiochemical yield of [ 11C] 1 was 9% (non-decay corrected) with a specific activity of 36 GBq/μmol at the end of synthesis. The average time of synthesis including formulation was 13.2 min with a radiochemical purity >98%. In vivo assessment of [ 11C] 1 was performed in a healthy Papio hamadryas baboon using positron emission tomography (PET). Following iv administration of [ 11C] 1, significant accumulation was observed in the baboon brain and peripheral organs. In the brain, the radioactivity peaked at 20 min and remained constant for the duration of the imaging experiment. Pre-treatment with the PBR-specific ligand, PK 11195 (5 mg/kg), effectively reduced the binding of [ 11C] 1 at 60 min by 70% in the whole brain, whereas pre-treatment with the central benzodiazepine receptor ligand, flumazenil (1 mg/kg), had no inhibitory effect on [ 11C] 1 uptake. These results indicate that accumulation of [ 11C] 1 in the baboon represents selective binding to the PBR. These exceptional in vivo binding properties suggest that [ 11C] 1 may be useful for imaging the PBR in disease states. Furthermore, [ 11C] 1 represents the first ligand of its pharmacological class to be labelled for PET studies and therefore has the potential to generate new information on the pathological role of the PBR in vivo.

Molecular Targets of New 1,4-Benzodiazepin-2-one Derivatives Influencing the Appetite of Experimental Animals

In order to establish the molecular targets of 1,4-benzodiazepin-2-ones mediating their influence on the appetite, the ability of 18 representatives of this class of compounds to bind to the central and peripheral benzodiazepine, dopamine (D1, D2), serotonin (5HT1A) and cholecystokinin (CCK2) receptors in the rat brain has been studied. The anorexigenic activity of some compounds is related to their ability to bind to CCK2 receptor, while the orexigenic activity of 7-bromo-5-(o-chloro)phenyl-1,2-dihydro-3H-1,4-benzodiazepin-2-one (phenazepam) is due to its high affinity to central benzodiazepine receptors.

Evaluating molecular similarity using reduced representations of the electron density

A model system of four benzodiazepine-like ligands for the central benzodiazepine receptors (CBRs) and peripheral benzodiazepine receptors (PBRs)is examined using a genetic algorithm procedure (GAGS) designed for evaluating molecular similarity. The method is based on the alignment of reduced representations generated from the critical points of the electron density computed at medium crystallographic resolution. The results are further characterized by a comparison with alignments produced by MIMIC, a field-based superimposition method that matches both steric and electrostatic molecular fields. The alignments produced by the two methods are generally seen to be consistent. The relationships of the compounds' binding affinities for both CBRs and PBRs to the alignments determined by GAGS yield a set of structural features required for significant binding to benzodiazepine receptors. Benefits of using reduced representations for evaluating molecular similarities and for constructing pharmacophore models are discussed.

Effect of PK11195, a peripheral benzodiazepine receptor agonist, on insulinoma cell death and insulin secretion

Functional role of peripheral benzodiazepine receptor on mitochondrial membrane in apoptosis and insulin secretion from insulinoma cells was studied. A prototypic peripheral benzodiazepine receptor agonist PK11195 induced insulinoma cell apoptosis, while a central benzodiazepine receptor agonist did not. Death of insulinoma cells by PK11195 was inhibited by cyclosporin A, a blocker of mitochondrial permeability transition pore. Caspase inhibitors further inhibited MIN6N8 cell death. PK11195 induced dissipation of mitochondrial potential and cytochrome c translocation to cytoplasm. PK11195 induced an increase in cytoplasmic [Ca(2+)], which was reversed by cyclosporin A. Rhod-2 staining showed decreased mitochondrial [Ca(2+)] after PK11195 treatment. PK11195 potentiated glucose-induced insulin secretion probably due to the increased cytoplasmic [Ca(2+)]. Calpain was activated following Ca(2+) release, and calpain inhibitors attenuated death of insulinoma cells by PK11195. These results suggest that PK11195 induces mitochondrial potential loss, cytochrome c translocation, increased insulin secretion in conjunction with an increase in cytoplasmic [Ca(2+)] and calpain activation, which collectively leads to apoptosis of insulinoma cells.

Free Communications: Pathogenesis

Abstract Neurotransmitter Receptor Densities in Patients with Grade II Focal Cortical Dysplasia: Correlation with Clinical Characteristics. 1,2 Michiyo Kageyama, 1 Kazumi Matsuda, 1 Shigeko Nishimura, 1 Yuko Kubota, 1 Takayasu Tottori, 1 Tadahiro Mihara, 1 Kazuichi Yagi, 1 Koichi Baba, 1 Naotaka Usui, 1 Shuichi Umeoka, and 1 Tateki Fujiwara ( 1 Shizuoka Institute of Epilepsy and Neurological Disorders 2 Shizuoka Prefectural Psychiatric Hospital, Shizuoka, Japan ). Purpose: We previously investigated the neurotransmitter receptors in focal cortical dysplasia (FCD) by examining resected cortex samples from patients with intractable epilepsy. Quantitative studies demonstrated decreases in receptor densities in more severely dysplastic lesions, and showed great individual variations in receptor densities especially in Palmini Grade II FCD cases. To find the background of the variation in receptor densities in Grade II FCD, we conducted a quantitative analysis of receptor densities by in vitro autoradiography and examined the correlation with clinical characteristics. Methods: Twenty resected specimens from patients with intractable localization-related epilepsy were obtained. The ages at onset were 0–14 years (means ± SD: 6.5 ± 5.1 years); the ages at operation were 2–31 years (19.1 ± 10.2 years); and the intervals from onset to operation were 2–30 years (12.6 ± 8.6 years). Seizures occurred daily (n = 10), weekly (n = 8), or monthly (n = 2). The specimens were immediately frozen and used for in vitro autoradiography using 3H-CGP39653 as the ligand of N-methyl-d-asparate receptor (NMDAR), 3H-AMPA as the ligand of α-amino-3-hydroxy-5-methyl-4-isoxazol propionate receptor (AMPAR), and 125I-iomazenil as the ligand of the central benzodiazepine receptor (c-BZR). Histopathologic examinations were conducted in the specimens adjacent to those used for receptor density analysis, and confirmed a diagnosis of FCD in all cases. The lesions were classified according to severity of dysplasia into these three groups (Palmini 1994): Grades I, II, and III. In Grade II lesions, the receptor densities were quantified on the autoradiogram. Statistical analyses were performed using Spearman's rank correlation (ρ) to examine the correlation between receptor densities and three clinical characteristics; onset age, operation age, and interval from onset to operation. The correlation between receptor densities and seizure frequency was also analyzed using Kruskal-Wallis test and Scheffe's test as post hoc test. Results: (1) The mean receptor densities (fmol/mg tissue) in Grade II lesions were NMDAR: 42.7 (SD = 20.7); AMPAR: 14.2 (SD = 8.9); and c-BZR: 56.5 (SD = 28.9). (2) c-BZR densities correlated significantly with onset age (ρ= 0.722, p = 0.0016) and interval from onset to operation (ρ= 0.759, p = 0.0009). (3) NMDAR and AMPAR densities showed no significant correlation with clinical characteristics. Seizure frequency did not correlate with any receptor density. Conclusion: A positive correlation was found between c-BZR density and onset age or interval from onset to operation. Since c-BZR density showed a higher correlation with interval from onset to operation than with onset age, c-BZR may increase not only with age but also with disease progression. This result suggests the possible existence of a long-term inhibitory feedback mechanism in response to excitation in the epileptogenic area of Grade II FCD in patients with intractable epilepsy.

Biological properties of 2′-[ 18F]fluoroflumazenil for central benzodiazepine receptor imaging

A novel positron emitting agent, 2′-[ 18F]fluoroflumazenil (fluoroethyl 8-fluoro-5-methyl-6-oxo-5,6-dihydro-4 H-benzo-[ f]imidazo[1,5- a][1,4]diazepine-3-carboxylate, FFMZ), has been reported for benzodiazepine imaging. In the present study, biological properties of [ 18F]FFMZ were investigated. Stability tests of [ 18F]FFMZ in human and rat sera were performed. Biodistribution was investigated in mice and phosphorimages of brains were obtained from rats. A receptor binding assay was performed using rat brain (mixture of cortex and cerebellum) homogenate. A static positron emission tomography (PET) image was obtained from a normal human volunteer. Although [ 18F]FFMZ was stable in human serum, it was rapidly hydrolyzed in rat serum. The hydrolysis was 39%, 63% and 92% at 10, 30 and 60 min, respectively. According to the biodistribution study in mice, somewhat even distribution (between 2∼3% ID/g) was observed in most organs. Intestinal uptake increased up to 6% ID/g at 1 h due to biliary excretion. Bone uptake slowly increased from 1.5% to 3.5% ID/g at 1 h. High uptakes in the cortex, thalamus and cerebellum, which could be completely blocked by coinjection of cold FMZ, were observed by phosphorimaging study using rats. Determination of K d value and B max using rat brain tissue was performed by Scatchard plotting and found 1.45±0.26 nM and 1.08±0.03 pmol/mg protein, respectively. The PET image of the normal human volunteer showed high uptake in the following decreasing order: frontal cortex, temporal cortex, occipital cortex, cerebellum, parietal cortex and thalamus. In conclusion, the new FMZ derivative, [ 18F]FFMZ appears to be a promising PET agent for central benzodiazepine receptor imaging with a convenient labeling procedure and a specific binding property.

Novel anellated pyrazoloquinolin-3-ones: synthesis and in vitro BZR activity

A series of pyrazolo[4,3- c]pyrrolo[3,2- f]quinolin-3-one derivatives 6, 7a– c, 8a, b, 9a, b and 10– 12 were synthesized as modified pyrazoloquinolinone analogs (PQs) and evaluated for their ability to inhibit radioligand to central and peripheral benzodiazepine receptors (BZRs) and their effect on GABA A α 1β 2γ 2L receptors expressed in Xenopus laevis oocytes. Multistep synthesis starting from 5-nitroindole, via the Gould–Jacobs reaction to the quinoline nucleus, yielded key intermediates 9-chloro-3 H-pyrrolo[3,2- f]quinoline-8-carboxylates. The reaction of the latter with methyl-hydrazine and various phenyl-hydrazines furnished the final compounds. In order to confirm the expected tetracyclic 2-substituted-2 H-pyrazolopyrroloquinolin-3-one structure, IR spectrophotometric, mono- 1H and 13C and bi-dimensional spectrometric and HRMS analyses were carried out: all compounds were found to be 2-substituted 3-keto tautomers; compound 6 only differed because it turned out to be 1-methyl-2 H-pyrazolo[4,3- c]pyrrolo[3,2- f]quinolin-3-olo. The results of this work are consistent with those previously reported for PQs: 7– 9 show high potency in displacing specific [ 3H]flunitrazepam from its receptor site; no compound was active in inhibiting the binding of [ 3H]PK 11195. They all act as antagonists at central BZR.

High Affinity Central Benzodiazepine Receptor Ligands: Synthesis and Biological Evaluation of a Series of Phenyltriazolobenzotriazindione Derivatives

A series of 2-phenyl[1,2,3]triazolo[1,2-a][1,2,4]benzotriazin-1,5(6H)-diones (PTBTs), VII, were prepared and tested at the central benzodiazepine receptor (BzR). The skeleton of these compounds was designed by formally combining the N-C=O moieties of the known BzR ligands, triazoloquinoxalines (IV) and triazinobenzimidazoles (ATBIs) (VI). Most of the PTBTs displayed submicromolar/nanomolar potency at the BzR. The 9-chloro derivatives (45-49) were generally found to be more potent than their 9-unsubstituted counterparts (37-44). Compound 45 turned out to be the most potent of the PTBTs (K(i) 2.8 nM). A subset of compounds (37, 42, 45, 49), when tested for their affinity on recombinant rat alpha1beta2gamma2, alpha2beta2gamma2, and alpha5beta3gamma2 GABA(A)/Bz receptor subtypes, showed enhanced affinities for the alpha1beta2gamma2 isoform, with compounds 45 and 49 exhibiting the highest selectivity. Moreover, compounds 45 and 49 were found to display a full agonist efficacy profile at alpha1 and alpha2 receptor subtypes, and an antagonist efficacy at alpha5-containing receptors.

Synthesis, Central and Peripheral Benzodiazepine Receptor Affinity of Pyrazole and Pyrazole‐Containing Polycyclic Derivatives.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Diazepam augments gender differences in cutaneous LD flux response to local cooling

Cutaneous vasoconstriction in response to local cooling is normally greater in females than in males. Cold induces amplification of α 2-adrenoceptor affinity for norepinephrine and increases reflex sympathetic thermoregulatory output. Benzodiazepines are drugs with very well-known binding to the central and peripheral benzodiazepine receptors. Besides these effects they decrease sympathetic output and as it was shown in the last decade they act synergistically with α-adrenoceptors. In the present study we tested the hypothesis that the benzodiazepine diazepam interacts with an α-adrenoceptor mechanism at the level of microcirculation. We measured laser-Doppler blood flux changes provoked by local cooling before and after oral application of a low dose of diazepam (5 mg) in 9 healthy males and in 11 healthy females with regular menstrual cycles. The results of our experiments show that in females there is a significant reduction (ANOVA, p < 0,05) in laser-Doppler flux during the first four minutes of cooling after taking of diazepam. In males, there is no significant difference in the responses to cold before and after an application of diazepam. Our results suggest that diazepam, in addition to its well-known effect on BZ receptors may also interact with α 2C-adrenoceptors in the vessel wall during local cooling.

Preparation of highly specific radioactivity [ 18F]flumazenil and its evaluation in cynomolgus monkey by positron emission tomography

A straightforward method for the preparation of no-carrier-added (n.c.a.) [ 18F]flumazenil via standard nucleophilic radiofluorination of the corresponding nitro-analog Ro 15-2344 has been developed. The labeling was performed by employing the K 18F/kryptofix complex in DMF at 160°C for 30 min and equimolar ratio [K/K2.2.2] +18F −/precursor. Under these conditions, an 18F incorporation rate into flumazenil was in the range of 55–60%. The final product was isolated by HPLC purification within a total synthesis time of 75 min and a radiochemical yield of about 30% (EOB). Human post-mortem whole-hemisphere autoradiography of brain sections demonstrated selective uptake of the radioligand in the areas of high density of the central benzodiazepine receptors (BZR). PET studies in a cynomolgus monkey and metabolite studies by HPLC demonstrated similar results by [ 18F]flumazenil as for [ 11C]flumazenil. In blocking experiments, almost all radioactivity was inhibited by the addition of unlabeled flumazenil. [ 18F]Flumazenil is a suitable radioligand for PET assessment of the BZR.

Structure−Activity Relationships and Effects on Neuroactive Steroid Synthesis in a Series of 2-Phenylimidazo[1,2-a]pyridineacetamide Peripheral Benzodiazepine Receptors Ligands

A series of 36 imidazopyridineacetamides (2-37) were designed and synthesized to evaluate the effects of structural changes on the amide nitrogen at both central (CBRs) and peripheral benzodiazepine receptors (PBRs). These changes include variations in the length and number of the alkyl groups as well as introduction of different aromatic, heteroaromatic, and conformationally constrained groups. The affinities of these compounds for CBRs and PBRs were determined, and the results indicate that bulkiness of the substituents, their branching, and length beyond an optimal value may cause hindrance to the ligand in its interaction with the receptor. The presence of aromatic or conformationally constrained substituents on the carboxamide nitrogen can be conducive to high affinity and selectivity. Furthermore, the ability of a subset of the most active ligands to stimulate synthesis of neuroactive steroids in plasma and brain was evaluated in vivo and in vitro. Compound 3 exhibited very marked effects on the peripheral and central synthesis of neuroactive steroids, while 36 (potent at subnanomolar level) showed a slight ability to affect neuroactive steroid content in the cerebral cortex.