In vitro assessment of the binding and functional responses of ozanimod and its plasma metabolites across human sphingosine 1-phosphate receptors.

Ozanimod is approved in multiple countries for the treatment of adults with either relapsing multiple sclerosis or moderately to severely active ulcerative colitis. Ozanimod is metabolized in humans to form seven active plasma metabolites, including two major active metabolites CC112273 and CC1084037, and an inactive metabolite. Here, the binding and activity of ozanimod and its metabolites across human sphingosine 1-phosphate receptors were determined. Binding affinity was assessed in Chinese hamster ovary cell membranes expressing recombinant human sphingosine 1-phosphate receptors 1 and 5 via competitive radioligand binding using tritium-labeled ozanimod; selectivity via functional potency assessment was performed using [35S]-guanosine-5'-(γ-thio)-triphosphate binding assays. Receptor internalization was assessed in human embryonic kidney 293 cells overexpressing sphingosine 1-phosphate receptor 1-green fluorescent protein and Chinese hamster ovary cells overexpressing sphingosine 1-phosphate receptor 5-hemagglutinin via fluorescence activated cell sorting. Functional activity was assessed in primary cultures of human astrocytes via phosphorylation assays. Ozanimod and its functionally active metabolites bound to the same sites within sphingosine 1-phosphate receptors 1 and 5, with metabolites displaying the same selectivity profile as ozanimod. Agonism at sphingosine 1-phosphate receptor 1 induced receptor internalization, whereas sphingosine 1-phosphate receptor 5 did not. Ozanimod, CC112273, and CC1084037 elicited functional intracellular signaling in human astrocytes, pharmacologically characterized to be mediated by sphingosine 1-phosphate receptor 1. The active plasma metabolites of ozanimod bound to sphingosine 1-phosphate receptors 1 and 5 and displayed similar pharmacologic profiles as their parent compound, likely contributing to clinical efficacy in patients with relapsing multiple sclerosis or moderately to severely active ulcerative colitis.

Exploring biological efficacy of novel benzothiazole linked 2,5-disubstituted-1,3,4-oxadiazole hybrids as efficient α-amylase inhibitors: Synthesis, characterization, inhibition, molecular docking, molecular dynamics and Monte Carlo based QSAR studies.

In an effort to explore a class of novel antidiabetic agents, we have made an effort to synergize the α-amylase inhibitory potential of 1,3-benzothiazole and 1,3,4-oxadiazole scaffolds by combining the two into a single structure via an ether linkage. The structure of synthesized benzothiazole clubbed oxadiazole derivatives are established by different spectral techniques. The synthesized hybrids are evaluated for their in vitro inhibitory potential against α-amylase. Compound 8f is found to be the most potent with a significant inhibition (87.5 ± 0.74% at 50 µg/mL, 82.27 ± 1.85% at 25 µg/mL and 79.94 ± 1.88% at 12.5 µg/mL) when compared to positive control acarbose (77.96 ± 2.06%, 71.17 ± 0.60%, 67.24 ± 1.16% at 50 µg/mL, 25 µg/mL and 12.5 µg/mL concentration). Molecular docking of the most potent enzyme inhibitor, 8f, shows promising interaction with the binding site of biological macromolecule Aspergillus oryzae α-amylase (PDB ID: 7TAA) and human pancreatic α-amylase (PDB ID: 3BAJ). To a step further, in-depth QSAR studies show a significant correlation between the experimental and the predicted inhibitory activities with the best Rvalidation2= 0.8701. The developed QSAR model can provide ample information about the structural features responsible for the increase and decrease of inhibitory activity. The mechanistic interpretation of the structure-activity relationship (SAR) is done with the help of combined computational calculations i.e. molecular docking and QSAR. Finally, molecular dynamic simulations are performed to get an insight into the binding mode of the most potent derivative with α-amylase from A. oryzae (PDB ID: 7TAA) and human pancreas (PDB ID: 3BAJ).

An efficient synthesis tetrazole and oxadiazole analogues of novel 2'-deoxy-C-nucleosides and their antitumor activity.

Various tetrazole and oxadiazole C-nucleoside analogues were synthesized starting from pure α- or ß-glycosyl-cyanide. The synthesis of glycosyl-cyanide as key precursor was optimized on gram-scale to furnish crystalline starting material for the assembly of C-nucleosides. Oxadizole C-nucleosides were synthesized via two independent routes. First,  the glycosyl-cyanide was converted into an amidoxime which upon ring closure offered an alternative pathway for the assembly of 1,2,4-oxadizoles in an efficient manner. Second, both anomers of glycosyl-cyanide were transformed into tetrazole nucleosides followed by acylative rearrangement to furnish 1,3,4-oxadiazoles in high yields. These protocols offer an easy access to otherwise difficult to synthesize C-nucleosides in good yield and protecting group compatibility. These C-nucleosides were evaluated for their antitumor activity. This work paves a path for facile assembly of library of new chemical entities useful for drug discovery.

A preclinical assessment to repurpose drugs to target type 1 diabetes-associated type B coxsackieviruses.

AIM: To screen several antiviral drugs systematically for their efficacy against type B coxsackieviruses. METHODS: Ten drugs with different antiviral mechanisms were analysed for their efficacy against prototype strains of type B coxsackieviruses in A549 cells. Cell viability was quantified in fixed cells using a colorimetric assay. Median effective dose was interpolated from the triplicated experiments and the dose-response curves were generated for each drug-virus combination. Drug cytotoxicity was similarly quantified and selectivity indices calculated. RESULTS: Hizentra, pleconaril, fluoxetine, norfluoxetine, ribavirin, favipiravir, and guanidine hydrochloride were able to abrogate infection by all tested viruses, with the exception of complete inefficacy of pleconaril against coxsackievirus B3 and favipiravir against coxsackievirus B2. The effective doses for Hizentra, enviroxime, ribavirin, favipiravir, and pleconaril were clearly below their therapeutic serum concentrations, while the effective concentrations of fluoxetin, norfluoxetine and itraconazole exceeded their therapeutic serum concentrations. Lovastatin and azithromycin did not efficiently block type B coxsackieviruses. CONCLUSION: Hizentra, enviroxime, pleconaril, ribavirin, and favipiravir are effective against type B coxsackieviruses in vitro in their therapeutic serum concentrations. These antiviral drugs are therefore attractive candidates for type 1 diabetes prevention/treatment trials. They can also be used in other clinical conditions caused by type B coxsackieviruses.

A mini-review and implementation model for using ataluren to treat nonsense mutation Duchenne muscular dystrophy.

AIM: Ataluren has been approved for treating nonsense mutation Duchenne muscular dystrophy (nmDMD), and there are currently discussions concerning drug access and applications beyond the development programme. This study provides an overview of nmDMD and ataluren, stipulates clinical rules for treatment initiation and discontinuation and proposes a model for the implementation of orphan drugs in clinical practice in Sweden. METHODS: This was a targeted mini-review of the literature from 1995 to 2018, which included cohort studies, guidelines, randomised clinical trials, clinical commentaries and reviews. The review covered the pathophysiology, epidemiology and burden of nmDMD and the clinical programme for ataluren. RESULTS: Based on the current evidence, and our experiences, we recommend that patients with nmDMD should be given ataluren as soon as possible after diagnosis and this treatment should continue until they reach a forced vital capacity of <30%, and, or, a score of at least six on the Brooke upper extremity scale. We propose an implementation model that comprises a coordinating specialist physician and a national expert committee responsible for providing clinical intelligence to ensure appropriate use. CONCLUSION: Our clinical recommendations and proposed implementation model will inform the optimum medical management of nmDMD in Sweden and help ensure timely, equal access to ataluren and similar orphan drugs.

Novel hybrids of benzothiazole-1,3,4-oxadiazole-4-thiazolidinone: Synthesis, in silico ADME study, molecular docking and in vivo anti-diabetic assessment.

A series of new benzothiazole-1,3,4-oxadiazole-4-thiazolidinone hybrid analogs (Tz1-Tz28) were synthesized in search of potential anti-diabetic agents. Molecular docking study was conducted with binding pocket of peroxisome proliferator activated receptor-gamma to elucidate the binding interactions of newly synthesized targets. Seven selected compounds with best docking scores were further screened for in vivo anti-hyperglycemic efficacy by oral glucose tolerance test in non-diabetic rats and on streptozotocin induced diabetic rat models. All the tested compounds demonstrated excellent to moderate reduction in blood glucose levels. Three of the compounds (Tz21, Tz7 and Tz10) showed excellent anti-diabetic effect by reducing concentration of glucose to 157.15 ±â€¯1.79 mg/dL, 154.39 ±â€¯1.71 mg/dL, 167.36 ±â€¯2.45 mg/dL, respectively better than the standard drug, pioglitazone, 178.32 ±â€¯1.88 mg/dL. Moreover, three derivatives Tz21, Tz4 and Tz24 with IC50 values of 0.21 ±â€¯0.01 µM, 9.03 ±â€¯0.12 µM and 11.96 ±â€¯0.40 µM respectively also showed better inhibitory activities on alpha-glucosidase even more than the standard acarbose (IC50 = 18.5 ±â€¯0.20 µM), indicating Tz21 has the highest inhibitory effect among the seven tested derivatives. Prediction of Drug like properties using molinspiration online software suggests that all the synthesized compounds have potential of becoming the orally active molecules. Thus, these novel hybrids could serve as potential candidates to become leads for the development of new drugs eliciting anti-hyperglycemic effect orally.

In vitro and in vivo assessment of newer quinoxaline-oxadiazole hybrids as antimicrobial and antiprotozoal agents.

A new series of N-(substituted-phenyl)-2-[5-(quinoxalin-2-yloxymethyl)-[1,3,4] oxadiazol-2-ylsulfanyl]-acetamides (5a-o) was designed and synthesised from the parent compound 2-hydroxy quinoxaline (1) through a multistep reaction sequence and was characterised by spectral and elemental analyses. All of the compounds synthesised were evaluated for their antimicrobial and antiprotozoal activities. The results revealed that quinoxaline-based 1,3,4-oxadiazoles displayed promising antibacterial, antifungal and anti-Trypanosoma cruzi activities compared with reference drugs, particularly the lead compound 5l in a short-term in vivo model in T. cruzi.

A field-based disparity analysis of new 1,2,5-oxadiazole derivatives endowed with antiproliferative activity.

A series of 1,2,5-oxadiazoles were synthesized as new potential antiproliferative agents. The in vitro cytotoxic activity evaluation of title compounds through MTT assay revealed that some of them showed significant activity against the HCT-116 cancer cell line. The field-based disparity analysis provided indications about the electrostatic, hydrophobic, and shape features underlying the cytotoxicity, suggesting that increasing the negative electrostatic field on the heterocyclic core of the structure has positive effects on the activity. The structure-activity relationships (SAR) around a particular compound can be explained allowing for a structural rationale for the differences in activity. The SAR provided by this series of compounds can be exploited to carry out further lead optimization.

Novel N-Acetyl Bioisosteres of Melatonin: Melatonergic Receptor Pharmacology, Physicochemical Studies, and Phenotypic Assessment of Their Neurogenic Potential.

Herein we present a new family of melatonin-based compounds, in which the acetamido group of melatonin has been bioisosterically replaced by a series of reversed amides and azoles, such as oxazole, 1,2,4-oxadiazole, and 1,3,4-oxadiazole, as well as other related five-membered heterocycles, namely, 1,3,4-oxadiazol(thio)ones, 1,3,4-triazol(thio)ones, and an 1,3,4-thiadiazole. New compounds were fully characterized at melatonin receptors (MT1R and MT2R), and results were rationalized by superimposition studies of their structures to the bioactive conformation of melatonin. We also found that several of these melatonin-based compounds promoted differentiation of rat neural stem cells to a neuronal phenotype in vitro, in some cases to a higher extent than melatonin. This unique profile constitutes the starting point for further pharmacological studies to assess the mechanistic pathways and the relevance of neurogenesis induced by melatonin-related structures.

Azilsartan medoxomil: a new Angiotensin receptor blocker.

BACKGROUND: Azilsartan medoxomil is an angiotensin receptor blocker, approved on February 25, 2011 by the US Food and Drug Administration (FDA) for hypertension management. OBJECTIVE: The purpose of this study was to review the pharmacology, pharmacokinetics, efficacy, safety profile, and role of azilsartan for hypertension management. METHODS: Peer-reviewed clinical trials, review articles, and relevant treatment guidelines were identified from MEDLINE and Current Contents (both 1966 to August 31, 2011) using the search terms azilsartan, TAK-491, TAK-536, pharmacology, pharmacokinetics, pharmacodynamics, pharmacoeconomics, and cost-effectiveness. The FDA Web site and manufacturer prescribing information were also reviewed to identify other relevant information. RESULTS: Compared with olmesartan 40 mg daily, azilsartan 80 mg reduced mean systolic blood pressure (SBP) by an additional 2.1 mm Hg (P = 0.038), whereas azilsartan 40 mg was noninferior to olmesartan 40 mg. Azilsartan 40 mg or 80 mg added to chlorthalidone 25 mg daily significantly reduced SBP to a greater extent than did chlorthalidone alone (P < 0.05), but there was no difference between azilsartan 40 mg and 80 mg (40 mg: -31.72 mm Hg; 80 mg: -31.3 mm Hg [P > 0.05]). When coadministered with amlodipine 5 mg daily, both azilsartan 40 mg and 80 mg + amlodipine decreased SBP significantly more than amlodipine alone (amlodipine: -13.6 mm Hg; with azilsartan 40 mg: -24.79 mm Hg; with azilsartan 80 mg: -24.51 mm Hg [P < 0.05]). Compared with ramipril 10 mg daily, both azilsartan 40 mg and 80 mg resulted in significantly (P < 0.001) greater reductions in mean SBP (-20.63 and -21.24 mm Hg, respectively; ramipril: -12.22 mm Hg). The most common adverse events reported were dizziness (4%), dyslipidemia (3.3%), and diarrhea (2%). CONCLUSIONS: At the recommended dose of 80 mg once daily, azilsartan is reported to be an efficacious BP-lowering agent. With once-daily dosing and a favorable side-effect profile, azilsartan is an attractive option for the treatment of hypertension. There is a lack of data supporting the use of azilsartan for improvement in cardiovascular outcomes; therefore, azilsartan is not approved for indications other than the treatment of hypertension.

Azilsartan: a newly approved angiotensin II receptor blocker.

Hypertension is a common chronic disease that leads to significant cardiovascular morbidity and mortality. Blood pressure control is essential to prevent end-organ complications, such as stroke, myocardial infarction, heart failure, or kidney disease. Azilsartan is the eighth angiotensin II receptor blocker approved for the management of hypertension, alone or in combination with other agents. At the approved dosage, it reduces systolic blood pressure by 12 to 15 mm Hg and diastolic blood pressure by 7 to 8 mm Hg. A higher dose of azilsartan (80 mg) was superior to valsartan 320 mg or olmesartan 40 mg in lowering systolic blood pressure in short-term studies. Additional blood pressure reduction is expected when azilsartan is used adjunctively with a diuretic. However, the effects of azilsartan on cardiovascular morbidity or mortality are still lacking. Azilsartan is well tolerated; the most common side effects are headache and diarrhea. No cases of hyperkalemia have been reported in 6-week clinical trials. Worsening of renal function and hypotension should be monitored, particularly in those with baseline risk factors. It is unknown whether azilsartan would join angiotensin-converting enzyme inhibitors and other angiotensin receptor blockers as the preferred hypertensive agents for end-organ protection. At this time, azilsartan should be considered as an alternative agent for mild-to-moderate hypertension, or as an adjunctive therapy when preferred agents fail to maintain optimal blood pressure control. It is also an option for those patients who have contraindications or cannot tolerate other antihypertensive agents, including dry cough induced by angiotensin-converting enzyme inhibitors.

Assessment of α7 nicotinic acetylcholine receptor availability in juvenile pig brain with [¹8F]NS10743.

PURPOSE: To conduct a quantitative PET assessment of the specific binding sites in the brain of juvenile pigs for [(18)F]NS10743, a novel diazabicyclononane derivative targeting α7 nicotinic acetylcholine receptors (α7 nAChRs). METHODS: Dynamic PET recordings were made in isoflurane-anaesthetized juvenile pigs during 120 min after administration of [(18)F]NS10743 under baseline conditions (n = 3) and after blocking of the α7 nAChR with NS6740 (3 mg·kg(-1) bolus + 1 mg·kg(-1)·h(-1) continuous infusion; n = 3). Arterial plasma samples were collected for determining the input function of the unmetabolized tracer. Kinetic analysis of regional brain time-radioactivity curves was performed, and parametric maps were calculated relative to arterial input. RESULTS: Plasma [(18)F]NS10743 passed readily into the brain, with peak uptake occurring in α7 nAChR-expressing brain regions such as the colliculi, thalamus, temporal lobe and hippocampus. The highest SUV(max) was approximately 2.3, whereas the lowest uptake was in the olfactory bulb (SUV(max) 1.53 ± 0.32). Administration of NS6740 significantly decreased [(18)F]NS10743 binding late in the emission recording throughout the brain, except in the olfactory bulb, which was therefore chosen as reference region for calculation of BP(ND). The baseline BP(ND) ranged from 0.39 ± 0.08 in the cerebellum to 0.76 ± 0.07 in the temporal lobe. Pretreatment and constant infusion with NS6740 significantly reduced the BP(ND) in regions with high [(18)F]NS10743 binding (temporal lobe -29%, p = 0.01; midbrain: -35%, p = 0.02), without significantly altering the BP(ND) in low binding regions (cerebellum: -16%, p = 0.2). CONCLUSION: This study confirms the potential of [(18)F]NS10743 as a target-specific radiotracer for the molecular imaging of central α7 nAChRs by PET.

Membrane blebbing as an assessment of functional rescue of dysferlin-deficient human myotubes via nonsense suppression.

Mutations that result in the loss of the protein dysferlin result in defective muscle membrane repair and cause either a form of limb girdle muscular dystrophy (type 2B) or Miyoshi myopathy. Most patients are compound heterozygotes, often carrying one allele with a nonsense mutation. Using dysferlin-deficient mouse and human myocytes, we demonstrated that membrane blebbing in skeletal muscle myotubes in response to hypotonic shock requires dysferlin. Based on this, we developed an in vitro assay to assess rescue of dysferlin function in skeletal muscle myotubes. This blebbing assay may be useful for drug discovery/validation for dysferlin deficiency. With this assay, we demonstrate that the nonsense suppression drug, ataluren (PTC124), is able to induce read-through of the premature stop codon in a patient with a R1905X mutation in dysferlin and produce sufficient functional dysferlin (approximately 15% of normal levels) to rescue myotube membrane blebbing. Thus ataluren is a potential therapeutic for dysferlin-deficient patients harboring nonsense mutations.

Vasorelaxant effect in rat aortic rings through calcium channel blockage: a preliminary in vitro assessment of a 1,3,4-oxadiazole derivative.

The study was undertaken on the basis of several reports in the literature that relaxation of vascular smooth muscles is a good treatment strategy in hypertension, angina and other cardiovascular disorders. Oxadiazoles have been reported to have effect on vascular smooth muscles and calcium influx. The goals of our current in vitro study were to investigate the effect of a 1,3,4-oxadiazole derivative on vascular smooth muscles in rat aorta, and to elucidate the associated signaling pathway. NOX-1 induced a relaxation of vascular smooth muscles in both endothelium intact and denuded rat aortic rings precontracted with norepinephrine or phenylephrine or KCl. NOX-1 also significantly antagonized cumulative dose-response effect of norepinephrine, phenylephrine, KCl or calcium with reduction in submaximal contractions. Verapamil, an L-type of calcium channel blocker, effectively attenuated phenylephrine and calcium induced contractions in aortic rings. Incubation with NOX-1 and verapamil did not significantly alter the dose-response curve of phenylephrine or calcium compared to verapamil treatment alone indicating L-type Ca2+ channel blockage leads to loss of NOX-1 activity. Hence it can be concluded NOX-1 exhibited vasorelaxant action by inhibiting calcium influx from extracellular space to intracellular space through L-type of calcium channels.

Optimization of azoles as anti-human immunodeficiency virus agents guided by free-energy calculations.

Efficient optimization of an inactive 2-anilinyl-5-benzyloxadiazole core has been guided by free energy perturbation (FEP) calculations to provide potent non-nucleoside inhibitors of human immunodeficiency virus (HIV) reverse transcriptase (NNRTIs). An FEP "chlorine scan" was performed to identify the most promising sites for substitution of aryl hydrogens. This yielded NNRTIs 8 and 10 with activities (EC50) of 820 and 310 nM for protection of human T-cells from infection by wild-type HIV-1. FEP calculations for additional substituent modifications and change of the core heterocycle readily led to oxazoles 28 and 29, which were confirmed as highly potent anti-HIV agents with activities in the 10-20 nM range. The designed compounds were also monitored for possession of desirable pharmacological properties by use of additional computational tools. Overall, the trends predicted by the FEP calculations were well borne out by the assay results. FEP-guided lead optimization is confirmed as a valuable tool for molecular design including drug discovery; chlorine scans are particularly attractive since they are both straightforward to perform and highly informative.

In vivo electrophysiological assessment of the putative antidepressant Wf-516 in the rat raphe dorsalis, locus coeruleus and hippocampus.

Wf-516 is a potential novel antidepressant. It has high affinity for serotonin (5-hydroxytryptamine; 5-HT) transporters, 5-HT(1A) and 5-HT(2A) receptors. In the present study, the pharmacologic properties of Wf-516 were thus assessed using in vivo electrophysiology in the rat dorsal raphe nucleus (DRN), locus coeruleus (LC) and hippocampus. Glass microelectrodes were lowered into the DRN, LC or hippocampus, and neurons were recorded and tested using systemic or microiontophoretic injections of drugs. In the DRN, cumulative doses of 0.5 mg/kg of Wf-516 were injected intravenously and total inhibition of 5-HT neurons firing was obtained with 2.8 +/- 0.3 mg/kg. The administration of 1 mg/kg of Wf-516, which by itself did not induce a change in the firing of 5-HT neurons, markedly attenuated the inhibitory effect of the 5-HT(1A) autoreceptor agonist LSD, indicating that Wf-516 is a 5-HT(1A) autoreceptor antagonist. In the LC, 1 mg/kg of Wf-516 dampened the inhibitory effect of the preferential 5-HT(2A) agonist DOI on norepinephrine (NE) neurons, indicating that Wf-516 is also a 5-HT(2A) receptor antagonist. In the hippocampus, cumulative intravenous doses of Wf-516 significantly increased the recovery time of firing activity of CA(3) pyramidal neurons after 5-HT applications, indicating an inhibitory effect on 5-HT reuptake. Unlike the 5-HT(1A) antagonist WAY100635, Wf-516 did not block the inhibitory effect of microiontophoretic application of 5-HT, indicating that this drug is devoid of 5-HT(1A) receptor antagonistic activity in this postsynaptic structure. These properties of WF-516 define the transporter/receptorial profile of an antidepressant with superior effectiveness.

In vivo assessment of safety and mechanisms underlying in vitro relaxation induced by Mikania laevigata Schultz Bip. ex Baker in the rat trachea.

Mikania laevigata, popularly known in Brazil as "guaco", is largely used in folk medicine against respiratory diseases. However, neither the assessment of the toxicity of "guaco" syrup (GS, used by humans) nor its efficacy or mechanisms of action has been properly investigated. Using in vitro procedures, we showed that the hydroalcoholic extract (HE) from Mikania laevigata induces a concentration-dependent relaxation of rat trachea which does not depend on epithelium-derived substances but involves changes in the cellular mobilization of calcium, perhaps due to a direct effect on membrane potassium channels. In addition, we assessed both oral and intraperitoneal acute toxicity, as well as the oral subchronic and chronic toxicity of GS containing controlled amounts of coumarin, the main biological marker of Mikania laevigata preparations used in humans. The calculated LD(50) of GS after intraperitoneal administration was 0.904 g/kg in mice (both sexes) and 0.967 and 0.548 g/kg in male and female rats, respectively. However, the LD(50) values of GS by the oral route were calculated to be up to 10 g/kg, in both male and female mice and rats. Repeated dose 28- or 90-day oral treatment with GS (75, 150 and 300 mg/kg) did not produce any disturbances in the hematological or biochemical parameters of either male or female rats, nor did it provide evidence of toxicity in the hepatic, renal or pancreatic systems. Besides the mechanistic findings, our results provide evidence of the safety of Mikania laevigata in rodents, even after subchronic and chronic administration, at least in relation to the evaluated parameters.

Assessment of Ca(2+)-antagonistic effect of SM-6586 and its isomers, novel 1,4-dihydropyridine derivatives, by radioligand binding assay.

The Ca(2+)-antagonistic effects of the 1,4-dihydropyridine derivative (+/-)SM-6586 and its optical isomers were compared with those of its two derivatives ((+/-)SM-7297 and (+/-)SM-7548) and other Ca(2+)-antagonists using a radioligand binding assay. The Ca(2+)-antagonistic effects of the optical isomers of SM-6586 were in the order of (+) greater than (+/-) greater than (-)SM-6586 in both rat brain and heart. The pKi value of (+)SM-6586 was comparable to those of nimodipine, nicardipine, nifedipine and nitrendipine. The pA2 value for (+)SM-6586 was the highest among the SM-6586 isomers, thus suggesting that (+)SM-6586 has a potent Ca(2+)-antagonistic effect.