Discovery of ONO-8590580: A novel, potent and selective GABAA α5 negative allosteric modulator for the treatment of cognitive disorders.

The identification and SAR development of a series of negative allosteric modulators of the GABAA α5 receptor is described. This novel series of compounds was optimised to provide analogues with high GABAA α5 binding affinity, high α5 negative allosteric modulatory activity, good functional subtype selectivity and low microsomal turnover, culminating in identification of ONO-8590580.

A tomographic spatial-unfolding method for Compton gamma imaging measurements.

An advanced spatial-unfolding technique capable of reconstructing the activity distribution within an exclusion zone from Compton gamma imager measurements taken outside of it is introduced. Although the method is generally applicable to extended sources, we demonstrate it here on a calibrated Cs-137 point source through Monte Carlo simulation studies as well as with measurements made using a Silicon Compton Telescope for Safety and Security (SCoTSS) gamma imager. For synthetic data the method accurately reconstructs the total activity contained within the mapped zone of interest, even when the size of the basis elements used to reconstruct the activity distribution is larger than the source itself. For experimental data, the method reliably located the source but underestimated its activity by up to 17%. This is accurate enough for real-world security applications. The underestimation is likely due to effects not yet included in the simulated response of the detector. The method has widespread applicability in the radiological/nuclear safety and security field, particularly for scenarios in which a threat material or contaminated area lies within a no-entry or no-fly zone.

Tomographic reconstruction of a spatially-extended source from the perimeter of a restricted-access zone using a SCoTSS compton gamma imager.

It is a standard procedure in many countries that response to a nuclear or radiological accident or incident would involve mobile aerial- or ground-based survey with highly sensitive gamma-ray detectors to map the distribution of radioactivity. There may however arise situations in which ground- or air-based detectors are not able to access an area to survey for radioactive materials, therefore technologies and techniques that can estimate the position and activity of radioactive materials from a distance are under development. Tomographic reconstruction methods, well-known in medical physics, permit the reconstruction of an N-dimensional map or image, from a number of N-1-dimensional cross-sectional images, or back-projections. We are investigating a tomographic reconstruction method to reconstruct the radioactivity distribution within a restricted-access zone using measurements from a Compton gamma imager placed at several locations around the perimeter of the zone. In this work an extended source of La-140 with an activity of 35 GBq was deposited within a 500 m by 500 m zone that was surveyed from the perimeter at six locations using a Silicon photomultiplier-based Compton Telescope for Safety and Security (SCoTSS) gamma imager. The reconstructed Compton images from multiple viewpoints were then projected back into the zone to reconstruct the distribution of La-140 within it. This tomographic method reconstructed high intensity along the known location of the La-140 source, suggesting that the method is able to localize the radioactive material. A simple fit to measured counts using a point-source approximation of the source distribution yielded a strength estimate of (7 ± 2) GBq at time of deposition, a reasonable result given the presence of soil and snow attenuation. Our method provides an expedient estimate of the distribution of radioactivity using tomographic techniques. It may be used to inform decisions made on the scene in urgent situations where the distribution of radioactivity must be reconstructed from a distance.

Intermittent versus continuous renal replacement therapy for acute renal failure in adults.

BACKGROUND: Renal replacement therapy (RRT) for acute renal failure (ARF) can be applied intermittently (IRRT) or continuously (CRRT). It has been suggested that CRRT has several advantages over IRRT including better haemodynamic stability, lower mortality and higher renal recovery rates. OBJECTIVES: To compare CRRT with IRRT to establish if any of these techniques is superior to each other in patients with ARF. SEARCH STRATEGY: We searched MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials (CENTRAL). Authors of included studies were contacted, reference lists of identified studies and relevant narrative reviews were screened. Search date: October 2006. SELECTION CRITERIA: RCTs comparing CRRT with IRRT in adult patients with ARF and reporting prespecified outcomes of interest were included. Studies assessing CAPD were excluded. DATA COLLECTION AND ANALYSIS: Two authors assessed trial quality and extracted data. Statistical analyses were performed using the random effects model and the results expressed as relative risk (RR) for dichotomous outcomes or mean difference (WMD) for continuous data with 95% confidence intervals (CI). MAIN RESULTS: We identified 15 studies (1550 patients). CRRT did not differ from IRRT with respect to in-hospital mortality (RR 1.01, 95% CI 0.92 to 1.12), ICU mortality (RR 1.06, 95% CI 0.90 to 1.26), number of surviving patients not requiring RRT (RR 0.99, 95% CI 0.92 to 1.07), haemodynamic instability (RR 0.48, 95% CI 0.10 to 2.28) or hypotension (RR 0.92, 95% CI 0.72 to 1.16) and need for escalation of pressor therapy (RR 0.53, 95% CI 0.26 to 1.08). Patients on CRRT were likely to have significantly higher mean arterial pressure (MAP) (WMD 5.35, 95% CI 1.41 to 9.29) and higher risk of clotting dialysis filters (RR, 95% CI 8.50 CI 1.14 to 63.33). AUTHORS' CONCLUSIONS: In patients who are haemodynamically stable, the RRT modality does not appear to influence important patient outcomes, and therefore the preference for CRRT over IRRT in such patients does not appear justified in the light of available evidence. CRRT was shown to achieve better haemodynamic parameters such as MAP. Future research should focus on factors such as the dose of dialysis and evaluation of newer promising hybrid technologies such as SLED. Triallists should follow the recommendations regarding clinical endpoints assessment in RCTs in ARF made by the Working Group of the Acute Dialysis Quality Initiative Working Group.

Continuous ambulatory peritoneal dialysis versus automated peritoneal dialysis for end-stage renal disease.

BACKGROUND: Peritoneal dialysis (PD) can be performed either manually as in continuous ambulatory peritoneal dialysis (CAPD) or using mechanical devices as in automated PD (APD). APD has been considered to have several advantages over CAPD such as reduced incidence of peritonitis, mechanical complications and greater psychosocial acceptability. OBJECTIVES: To assess the comparative efficacy of CAPD and APD in patients who are dialysed for end-stage renal disease (ESRD). SEARCH STRATEGY: We searched MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials (CENTRAL), Cochrane Renal Group's specialised register and CINAHL. Authors of included studies were contacted, reference lists of identified RCTs and relevant narrative reviews were screened. Date of most recent search: May 2006 SELECTION CRITERIA: RCTs comparing CAPD with APD in patients with ESRD. DATA COLLECTION AND ANALYSIS: Data were abstracted independently by two authors onto a standard form. Relative risk (RR) for dichotomous data and a mean difference (MD) for continuous data were calculated with 95% confidence intervals (CI). MAIN RESULTS: Three trials (139 patients) were included. APD did not differ from CAPD with respect to mortality (RR 1.49, 95% CI 0.51 to 4.37), risk of peritonitis (RR 0.75, 95% CI 0.50 to 1.11), switching from original PD modality to a different dialysis modality (RR 0.50, 95% CI 0.25 to 1.02), hernias (RR 1.26, 95% interval 0.32 to 5.01), PD fluid leaks (RR 1.06, 95% CI 0.11 to 9.83), PD catheter removal (RR 0.64, 95% CI 0.27 to 1.48) or hospital admissions (RR 0.96, 95% CI 0.43 to 2.17). There was no difference between either PD modality with respect to residual renal function (MD -0.17, 95% CI -1.66 to 1.32). One study found that peritonitis rates and hospitalisation were significantly less in patients on APD when results were expressed as episodes/patient-year. Another study found that patients on APD had significantly more time for work, family and social activities. AUTHORS' CONCLUSIONS: APD has not been shown to have significant advantages over CAPD in terms of important clinical outcomes. APD may however be considered advantageous in select group of patients such as in the younger PD population and those in employment or education due to its psychosocial advantages. There is a need for a RCT comparing CAPD with APD with sufficiently large patient numbers looking at important clinical outcomes including residual renal function, accompanied by an economic evaluation to clarify the relative clinical and cost-effectiveness of both modalities.

Haemodiafiltration, haemofiltration and haemodialysis for end-stage kidney disease.

BACKGROUND: Renal replacement therapy (RRT) for end-stage kidney disease (ESKD) can be achieved by several interventions including haemodialysis (HD), peritoneal dialysis (PD) and kidney transplantation. HD, haemofiltration (HF), haemodiafiltration (HDF) and acetate-free biofiltration (AFB) are extracorporeal RRT methods. It has been suggested that HF and HDF may reduce the frequency and severity of intradialytic and post-dialytic adverse symptoms and may be more effective than HD in the removal of high molecular weight molecules. OBJECTIVES: To compare convective modes of extracorporeal RRT (HF, HDF or AFB) with HD and to establish if any of these techniques is superior to each other in patients with ESKD. SEARCH STRATEGY: We searched MEDLINE (1966-2006), EMBASE (1980-2006), Cochrane Central Register of Controlled Trials (CENTRAL, in The Cochrane Library issue 2, 2006) and CINAHL (1872-2006). Authors of included studies were contacted, reference lists of identified RCTs and relevant narrative reviews were screened. SELECTION CRITERIA: RCTs comparing HF, HDF, AFB and HD for ESKD were included. Trials enrolling any patient undergoing RRT for ESKD were included. DATA COLLECTION AND ANALYSIS: Two authors independently assessed trial quality and extracted data. Statistical analyses were performed using the random effects model and the results expressed as relative risk (RR) for dichotomous outcomes or weighted mean difference (MD) for continuous data with 95% confidence intervals (CI). Heterogeneity was measured using the Chi-square (chi(2)) and I(2) statistic. MAIN RESULTS: Twenty studies (657 patients) were included. Seventeen studies compared HF, HDF or AFB with HD, two compared HDF with AFB and one compared HF with HDF. The studies were generally small with suboptimal quality. Convective modalities (HF, HDF, AFB) did not differ significantly from HD for mortality (RR 1.68, 95% CI 0.23 to 12.13; chi(2)= 2.58, P = 0.11, I(2) = 61.2%), number of hospital admissions/year (MD 0.20, 95% CI -0.07 to 0.47) and dialysis adequacy (Kt/V: MD 0.09, 95% CI 0.02 to 0.17; chi(2) = 3.73, P = 0.29, I(2) = 19.6%). No study assessed number of dialysis treatments associated with "any adverse symptoms", sessions that were stopped early, change of dialysis modality or dialysis-related amyloidosis. AUTHORS' CONCLUSIONS: We were unable to demonstrate whether convective modalities (either HF, HDF or AFB) have significant advantages over HD with regard to clinically important outcomes of mortality, dialysis-related hypotension and hospitalisation. More adequately-powered good quality RCTs assessing clinically important outcomes (mortality, hospitalisation, quality of life) are needed.

Active-site variants of Streptomyces griseus protease B with peptide-ligation activity.

BACKGROUND: Peptide-ligating technologies facilitate a range of manipulations for the study of protein structure and function that are not possible using conventional genetic or mutagenic methods. To different extents, the currently available enzymatic and nonenzymatic methodologies are synthetically demanding, sequence-dependent and/or sensitive to denaturants. No single coupling method is universally applicable. Accordingly, new strategies for peptide ligation are sought. RESULTS: Site-specific variants (Ser195-->Gly, S195G, and Ser195-->Ala, S195A) of Streptomyces griseus protease B (SGPB) were generated that efficiently catalyze peptide ligation (i.e., aminolysis of ester-, thioester- and para-nitroanilide-activated peptides). The variants also showed reduced hydrolytic activity relative to the wild-type enzyme. The ratio of aminolysis to hydrolysis was greater for the S195A variant, which was also capable of catalyzing ligation in concentrations of urea as high as 2 M. CONCLUSIONS: Mutagenic substitution of the active-site serine residue of SGPB by either glycine or alanine has created a unique class of peptide-ligating catalysts that are useful for coupling relatively stable ester- and para-nitroanilide-activated substrates. Ligation proceeds through an acyl-enzyme intermediate involving His57. Serine to alanine mutations may provide a general strategy for converting proteases with chymotrypsin-like protein folds into peptide-coupling enzymes.

Psychosocial interventions for depression in dialysis patients.

BACKGROUND: Depression is the most common psychological problem in the dialysis population. The diagnosis of depression in dialysis patients is confounded by the fact that several symptoms of uraemia mimic the somatic components of depression. It affects the physical, psychological and social well being of the dialysis population in several ways. OBJECTIVES: The aim of this systematic review was to assess the effectiveness of psychosocial interventions in the treatment of depression in patients who are dialysed for end-stage renal disease. SEARCH STRATEGY: A comprehensive search strategy was employed to identify all randomised controlled trials (RCTs) relevant to the treatment of depression in dialysis patients. The following databases were searched - MEDLINE (1966 - October 2003), EMBASE (1980 - October 2003), PsycINFO (1872 - October 2003) and The Cochrane Library (issue 3, 2003). Authors of potential studies were contacted, reference lists of identified RCTs and relevant narrative reviews were screened. SELECTION CRITERIA: RCTs comparing any psychosocial intervention with control intervention or no intervention in depressed dialysis patients. DATA COLLECTION AND ANALYSIS: Data were to be abstracted by two investigators independently onto a standard form and entered into Review Manager 4.2. Relative risk (RR) for dichotomous data and a (weighted) mean difference (MD) for continuous data were to be calculated with 95% confidence intervals (CI). MAIN RESULTS: Despite extensive searching, no RCTs were identified. AUTHORS' CONCLUSIONS: Data were not available to draw conclusions about the effectiveness of psychosocial interventions in the treatment of depression in the chronic dialysis population, as we did not find any RCTs of psychosocial interventions to treat depression in dialysis patients. This review highlights the need for commencing and completing adequately powered RCTs to address the issue of psychosocial interventions for depression in dialysis patients.

Physical measures for treating depression in dialysis patients.

BACKGROUND: Depression is the most common psychological problem in the chronic dialysis population. The diagnosis of depression in patients on chronic dialysis is confounded by the fact that several symptoms of uraemia mimic the somatic components of depression. It affects their physical, psychological and social well-being. Furthermore, the frequent occurrence of cardiovascular problems and the pharmacokinetic consequences of renal impairment may make drug treatment of depression difficult. OBJECTIVES: The aim of this systematic review was to assess the efficacy and safety of physical measures in the treatment of depression in patients who are dialysed for end-stage renal disease. SEARCH STRATEGY: A comprehensive search strategy was employed to identify all Randomised Controlled Trials (RCTs) relevant to the treatment of depression in patients on chronic dialysis. The following database were searched - MEDLINE (1966-March 2004), EMBASE (1980-March 2004), PSYCHINFO (1872-March 2004), The Cochrane Library (Issue 1, 2004). Authors of included studies were contacted, reference lists of identified RCTs and relevant narrative reviews were screened. SELECTION CRITERIA: RCTs comparing drugs with placebo or no treatment, or a comparison of drugs against a combination of electroconvulsive therapy and drugs. DATA COLLECTION AND ANALYSIS: Data were abstracted by two investigators independently onto a standard form and subsequently entered into Review Manager 4.2. Relative risk (RR) for dichotomous data and a (weighted) mean difference (WMD) for continuous data were calculated with 95% confidence intervals (95% CI). MAIN RESULTS: Only one trial, with a total of 12 patients and of eight weeks duration was identified. The trial compared fluoxetine against placebo in depressed patients on chronic dialysis. This study did not show any significant difference in depression scores between the treatment and control groups or safety. AUTHORS' CONCLUSIONS: Firm conclusions on the efficacy of physical methods of treatment cannot be made as we identified only one small RCT that was of short duration. More larger and longer term RCTs are needed in this area. Current screening tools for depression are recognised to have poor specificity in the medically ill due to overlap of somatic symptoms of the medical illness. The development of a valid diagnostic tool would be helpful.

Cellulose, modified cellulose and synthetic membranes in the haemodialysis of patients with end-stage renal disease.

BACKGROUND: When the kidney fails the blood-borne metabolites of protein breakdown and water cannot be excreted. The principle of haemodialysis is that such substances can be removed when blood is passed over a semipermeable membrane. Natural membrane materials include cellulose or modified cellulose, more recently various synthetic membranes have been developed. Synthetic membranes are regarded as being more "biocompatible" in that they incite less of an immune response than cellulose-based membranes. OBJECTIVES: To assess the effects of different haemodialysis membrane material in patients with end-stage renal disease (ESRD). SEARCH STRATEGY: We searched MEDLINE, EMBASE, PreMEDLINE, HealthStar CINAHL, the Cochrane Central Register of Controlled Trials (CENTRAL), Biosis, SIGLE, CRIB, UK National Research Register and reference lists of relevant articles. We contacted biomedical companies, known investigators and handsearched selected journals and conference proceedings. Date of most recent search: June 2004. SELECTION CRITERIA: All randomised controlled trials (RCTs) or quasi-RCTs comparing different haemodialysis membrane material in patients with ESRD. DATA COLLECTION AND ANALYSIS: Two reviewers independently assessed the methodological quality of studies. Data was abstracted onto a standard form by one reviewer and checked by another. Relative Risk (RR) and weighted mean difference (WMD) with 95% confidence intervals (CI)) MAIN RESULTS: Thirty two studies were identified. Pre-dialysis ss(2) microglobulin concentrations were not significantly lower in patients treated with synthetic membranes (WMD -14.67, 95% CI -33.10 to 4.05). When analysed for change in ss(2) microglobulin, a fall was only noted with high-flux membranes. The incidence of amyloid was less in patients who were dialysed for six years with high-flux synthetic membranes (one study, RR 0.03, 95% CI 0.00 to 0.54). There was a significant difference in favour of the synthetic (high-flux) membrane in comparison to cellulose membranes for triglycerides (WMD -0.66; 95% CI -1.18 to -0.14) but not for modified cellulose membranes. Dialysis adequacy measured by Kt/V was marginally higher when cellulose membranes were used (WMD -0.10; 95% CI -0.16 to 0.04), whereas synthetic membranes achieved significantly higher Kt/V values when compared with modified cellulose membranes (WMD 0.20, 95% 0.11 to 0.29) . There were no data on quality of life measures. AUTHORS' CONCLUSIONS: We found no evidence of benefit when synthetic membranes were compared with cellulose/modified cellulose membranes in terms of reduced mortality no reduction in dialysis-related adverse symptoms. Despite the relatively large number of RCTs undertaken in this area none of the included studies reported any measures of quality of life.

Measurement of regional cerebral blood flow with positron emission tomography: a comparison of [15O]water to [11C]butanol with distributed-parameter and compartmental models.

To further our understanding of the best way to measure regional CBF with positron emission tomography (PET), we directly compared two candidate tracers ([15O]water and [11C]butanol, administered intravenously) and two popular implementations of the one-compartment (1C) model: the autoradiographic implementation representing a single PET measurement of tissue radioactivity over 1 min and a dynamic implementation representing a sequence of measurements of tissue radioactivity over 200 s. We also examined the feasibility of implementing a more realistic, and thus more complex, distributed-parameter (DP) model by assigning fixed values for all of its parameters other than CBF and tracer volume of distribution (Vd), a requirement imposed by the low temporal resolution and statistical quality of PET data. The studies were performed in three normal adult human subjects during paired rest and visual stimulation. In each subject seven regions of interest (ROIs) were selected, one of which was the primary visual cortex. The corresponding ROI were anatomically equivalent in the three subjects. Regional CBF, Vd, tracer arrival delay, and dispersion were estimated for the dynamic data curves. A total of 252 parameter sets were estimated. With [11C]butanol both implementations of the 1C model provided similar results (r = 0.97). Flows estimated using the 1C models were lower (p < 0.01) with [15O]water than with [11C]butanol. In comparison with the 1C model, the constrained version of the DP used in these studies performed inadequately, overestimating high flow and underestimating low flow with both tracers, possibly as the result of the necessity of assigning fixed values for all of its parameters other than CBF and Vd.

Increased functional vascular response in the region of a glioma.

Functional imaging of a language task using positron emission tomography was performed as part of the preoperative assessment of a patient with a left supplementary motor area (SMA) tumor. Positron emission tomography scans were obtained during language tasks (verb generation and word reading of visually presented nouns) that normally lead to increased blood flow in the SMA relative to a control condition (visual fixation). In the patient, the normal SMA response was an order of magnitude larger in the region of the tumor. Other regions, such as left inferior frontal cortex and right cerebellum, showed equivalent activation in the patient and normal subjects. Histopathologic study revealed an anaplastic astrocytoma. Thus, this exaggerated vascular response to local neuronal activation occurred in the setting of a proliferation of glial cells. This is consistent with models of coupling of regional CBF and neuronal activity that implicate glia as the mediator between neurons and vasculature. The concept that tumoral disruption of normal vascular responses could, in some cases, potentially enhance rather than dampen the response is proposed.

Streptomyces lividans glycosylates an exoglucanase (Cex) from Cellulomonas fimi.

Exoglucanase Cex from Cellulomonas fimi is a glycoprotein [Langsford et al., J. Gen. Microbiol. 130 (1984) 1367-1376]. Cex produced by Streptomyces lividans from the cloned cex gene is also glycosylated. The extent and nature of glycosylation are similar for Cex from both organisms. The glycosylation affords protection against proteolysis for the enzymes from both organisms when they are bound to cellulose, but not in solution. The ability to glycosylate cloned gene products enhances the utility of Streptomyces as a host for the production of heterologous polypeptides.

Diminished regional cerebral blood flow response to vibration in patients with blepharospasm.

OBJECTIVE: To determine whether patients with blepharospasm have abnormal sensorimotor processing similar to patients with writer's cramp. BACKGROUND: Blepharospasm is a focal dystonia manifest by involuntary, excessive blinking and squeezing of the eyes. Altered sensorimotor processing may contribute to the development of dystonic movements. Previously the authors demonstrated decreased vibration-induced cortical blood flow responses in hand primary sensorimotor area (PSA) in patients with hand dystonia. METHODS: In this prospective, case-control study, seven patients with blepharospasm were compared with seven normal subjects. PET measurements of regional blood flow were obtained using bolus administration of H(2)15O at rest or during sequential vibration of either the left or the right hand or side of the mouth. RESULTS: PSA activation decreased significantly in the patients with blepharospasm both ipsilateral (-68%; p = 0.0004) and contralateral to the side of facial stimulation (-56%; p = 0.0009). Patients had a 31% lower mean contralateral PSA response to hand vibration and a 51% smaller right supplementary motor area response to left-hand vibration than normal subjects, but these differences did not reach statistical significance. CONCLUSIONS: Patients with blepharospasm have abnormal sensorimotor processing in response to lower face vibration. They may also have abnormal brain responses to stimulation of clinically uninvolved parts of the body, but this requires confirmation.

Tachykinin NK1 receptor antagonists act centrally to inhibit emesis induced by the chemotherapeutic agent cisplatin in ferrets.

These studies have compared the pharmacological profile of two non-peptide human type neurokinin1 (hNK1) receptor selective antagonists, L-741,671 and a quaternised compound L-743,310. In radioligand binding studies L-741,671 and L-743,310 had high affinity for ferret and cloned hNK1 receptors [Ki (nM) ferret 0.7 and 0.1; human 0.03 and 0.06, respectively] but low affinity for rodent NK1 receptors [Ki (nM) 64 and 17, respectively] suggesting that ferret receptors have hNK1-like binding pharmacology. Studies in vivo showed that L-741,671 and L-743,310 had equivalent functional activity in the periphery (ID50s of 1.6 and 2 micrograms/kg i.v., respectively) as measured by inhibition of plasma protein extravasation evoked in the oesophagus of guinea pigs by resiniferatoxin (7 nmol/kg i.v.). Using an in situ brain perfusion technique in anaesthetised rats, L-741,671 was shown to be much more brain penetrant than the quaternary compound L-743,310 which had an entry rate similar to the poorly brain penetrant plasma marker inulin. These compounds thus provided an opportunity to compare the anti-emetic effects of equi-active hNK1 receptor antagonists with and without brain penetration to central NK1 receptor sites. When tested against cisplatin-induced emesis in ferrets, L-741,671 (0.3, 1 and 3 mg/kg i.v.) produced marked dose-dependent inhibition of retching and vomiting but L-743,310 was inactive at 3 and 10 micrograms/kg i.v. In contrast, direct central injection of L-741,671 and L-743,310 (30 micrograms) into the vicinity of the nucleus tractus solitarius or L-743,310 (200 micrograms) intracisternally was shown to inhibit retching and vomiting induced by i.v. cisplatin. L-741,671 and L-743,310 had equivalent functional activity, at the same dose, against cisplatin-induced emesis when injected centrally. These observations indicated that had L-743,310 penetrated into the brain after systemic administration it would have been active in the cisplatin-induced emesis assay and so show that brain penetration is essential for the anti-emetic action of systemically administered NK1 receptor antagonists.

Identification of 3,5-dihydro-2-aryl-1H-pyrazolo[3,4-c]quinoline-1,4(2H)-diones as novel high-affinity glycine site N-methyl-D-aspartate antagonists.

Almost all of the existing known antagonists at the glycine site of the N-methyl-D-aspartate (NMDA) receptor have a low propensity for crossing the blood-brain barrier. It has been suggested that in many cases this may be due to the presence of a carboxylic acid which is a common feature of most of the potent full antagonists at this receptor. In this study, 2-aryl-1H-pyrazolo[3,4-c]quinoline-1,4(2H)-diones were found to have high-affinity binding at the glycine receptor. In particular, structure-activity studies identified 7-chloro-3,5-dihydro-2-(4-methoxyphenyl)-1H-pyrazolo[3,4-c]quinoline- 1,4(2H)-dione as the most potent of a series of analogues with an IC50 of 3.3 nM. The measured pKa values in this class of compounds (typically 4.0) indicate they are of equivalent acidity to carboxylic acids. Functional antagonism was demonstrated by inhibition of NMDA-evoked responses in rat cortical slices. Anticonvulsant activity in DBA/2 mice was achieved after dosing by direct injection into the cerebral ventricles, but no activity was seen after systemic administration, suggesting low brain penetration with this class of antagonists.

Tetrahydropyridyloxadiazoles: semirigid muscarinic ligands.

Recent studies have described novel azabicycle-based muscarinic agonists which readily penetrate into the central nervous system and are capable of displaying high efficacy at cortical sites. The current paper describes the synthesis and biochemical assessment of semirigid muscarinic ligands which were used to map the requirements of the cortical muscarinic receptor and to study the degree of conformational flexibility required to cause receptor activation. Analogues 6 and 9 provide high-efficacy muscarinic agonists at cortical sites; however, C-alkylation on the tetrahydropyridine ring resulted in more rigid analogues and showed lower predicted efficacy. Molecular mechanics calculations indicated a preference for the E rotameric form. This conformation was also observed in the X-ray crystal structure of ethenyloxadiazole 12. The new compounds were tested in a biochemical assay designed to measure receptor affinity and to predict cortical efficacy.

Identification of L-tryptophan derivatives with potent and selective antagonist activity at the NK1 receptor.

As part of a program of screening the Merck sample collection, N-ethyl-L-tryptophan benzyl ester was identified as a weak antagonist at the substance P (NK1) receptor. Structure-activity studies showed that the indole ring system could be replaced by 3,4-dichlorophenyl, alpha- or beta-naphthyl, or benzthiophene with retention or only small loss of affinity. It was found that acylation of the tryptophan nitrogen gave compounds with higher affinity than N-ethyl or other basic amines. Optimization of substitution on the benzyl ester led to the identification of the 3,5-bis-(trifluoromethyl)benzyl ester of N-acetyl-L-tryptophan 26 as a potent and selective substance P receptor antagonist. Compound 26 blocked substance P induced dermal extravasation in vivo and was the most potent compound from this structurally novel class of antagonists which further adds to the diversity of small molecules that bind to the (NK1) receptor.

Synthesis and muscarinic activities of 1,2,4-thiadiazoles.

A series of novel 1,2,4-thiadiazoles bearing a mono- or bicyclic amine at C5 were prepared. Quinuclidine and 1-azabicyclo[2.2.1]heptane derivatives were synthesized by reaction of the lithium enolate of the 3-methoxycarbonyl compounds followed by ester hydrolysis and decarboxylation. The receptor-binding affinity and efficacy of these compounds as muscarinic ligands was assessed by radioligand binding assays using [3H]-N-methylscopolamine and [3H]oxotremorine-M. Optimal agonist affinity was observed for 3'-methyl compounds. Smaller substituents (H) retained efficacy with reduced affinity while larger groups led to substantially lower efficacy. The observed binding affinity was influenced both by the conformational energy of rotation around the C3-C5' bond and the steric requirement of the mono- or bicyclic amine.

Tryptophan-derived NK1 antagonists: conformationally constrained heterocyclic bioisosteres of the ester linkage.

The 3,5-bis(trifluoromethyl)benzyl ester of N-acetyl-L-tryptophan 1 (L-732,138) has been identified previously as a potent and selective substance P receptor antagonist. A series of analogs which introduced a 6-membered heterocyclic ring into the backbone of this structure were prepared for evaluation as bioisosteric replacements of the ester linkage of 1. The 2,5-dioxopiperazine 2 had very weak receptor affinity, but 2-oxopiperazine 5 exhibited modest activity. Examination of the conformations accessible to the substituents on these templates led to exploration of the corresponding 5-membered heterocyclic rings. This study culminated in the identification of oxazolidinedione 14 as a suitable ester mimic in terms of the retention of good NK1 binding affinity.