Search PubMed⌕ Search

Biomedical subjects

A H Lewin

Publications and source records attributed to A H Lewin.

53 records · Page 3Linked to original sources
PubMed1991

Site-specific acylation of GABA-gated Cl- channels: effects on 36Cl- uptake.

Radioligand binding studies indicate that p-isothiocyanato-t-butylbicycloorthobenzoate (p-NCS-TBOB) specifically acylates GABA-gated chloride channels. Preincubation of synaptoneurosomes with p-NCS-TBOB followed by washing resulted in a concentration dependent (63-500 nM) inhibition of both muscimol-stimulated chloride uptake and [355]t-butylbicyclophosphorothionate (TBPS) binding. The extent of acylation (assessed by inhibition of [35S]TBPS binding) was highly correlated (r = 0.89; p less than 0.001) with the inhibition of muscimol-stimulated Cl- uptake. Neither basal Cl- uptake nor [3H]muscimol binding to GABAA receptors were affected by p-NCS-TBOB. Preincubation with the nonacylating 'cage' convulsant t-butylbicycloorthobenzoate (500 nM) followed by washing had no effect on either muscimol-stimulated Cl- uptake or [35S]TBPS binding. These findings indicate that p-NCS-TBOB interferes with the efficacy of muscimol promoted channel openings, but does not affect the recognition qualities of GABAA receptors. p-NCS-TBOB should prove useful in electrophysiological and biochemical studies examining the properties of GABA-gated Cl- channels.

Acylation↗
PubMed1991

Synthesis and ligand binding of cocaine isomers at the cocaine receptor.

The cocaine binding site at the dopamine transporter has been found to be stereoselective. Thus, the seven possible stereoisomers of (-)-cocaine have been synthesized and found to inhibit [3H]-2 beta-carbomethoxy-3 beta-(4-fluoro-phenyl)tropane [( 3H]WIN 35,428) with potencies ranging from 1/60 to 1/600 of that of (-)-cocaine. The synthesis and characterization of all new compounds is presented.

Animals↗
PubMed1991

Novel site-directed affinity ligands for GABA-gated chloride channels: synthesis, characterization, and molecular modeling of 1-(isothiocyanatophenyl)-4-tert-butyl-2,6,7-trioxabicyclo[2.2.2]octanes .

p-, m-, and o-isothiocyanate derivatives (1-3, respectively) of tert-butylbicycloorthobenzoate (TBOB) were synthesized from 3-tert-butyloxetane-3-methanol (4) as the starting material. While 2 was readily obtained in four steps via catalytic hydrogenation of the m-nitro-tert-butylbicycloorthobenzoate (9) intermediate, 1 and 3 could not be obtained this way. 1 and 3 were instead synthesized by an alternative four-step approach while made use of the stability of the isothiocyanate moiety to strong Lewis acids such as boron trifluoride etherate, conditions that would isomerize isothiocyanato oxetane ester intermediates to their corresponding orthoesters. The p-isothiocyanate derivative of TBOB, compound 1, inhibited [35S]-tert-butylbicyclophosphorothionate (TBPS) binding to rat cortical membranes with a potency (IC50 62 nM) comparable to the parent compound while 2 and 3 were approximately 10-fold less potent (IC50 values 570 and 609 nM, respectively). Preincubating tissue with radioligand further reduced the potencies of 2 and 3 by approximately 1 order of magnitude (IC50 values 5400 and 7500 nM, respectively) while the potency of 1 (IC50 90 nM) was only marginally affected by this procedure. Pretreatment of membranes with 1 and 2 followed by extensive washing resulted in a concentration-dependent inhibition of [35S]TBPS binding. In contrast, preincubating tissues with up to 2.4 microM of 3 did not elicit an apparent acylation of [35S]TBPS binding sites. Molecular modeling of the effective diameters of 1-3 in their thermodynamically most stable conformations indicates a relationship between these diameters and their relative efficacies as site-directed acylators; the smaller the diameter, the more potent the acylator. This hypothesis explains both the relative potencies of these compounds and their differential abilities to acylate the TBPS binding site.

Animals↗
PubMed1991

Synthesis, ligand binding, QSAR, and CoMFA study of 3 beta-(p-substituted phenyl)tropane-2 beta-carboxylic acid methyl esters.

A series of 3 beta-(p-substituted phenyl)tropane-2 beta-carboxylic acid methyl esters (2) were synthesized and found to possess high affinity for the cocaine binding site in rat striatum. The p-chloro (2c) and p-iodo (2n) compounds, which were the most potent analogues prepared, were found to be 85 and 78 times more potent than (-)-cocaine. The p-bromo (2m) and p-methyl (2d) were also 56 and 60 times more potent than cocaine. QSAR and CoMFA studies were conducted to correlate binding affinity of the cocaine analogues with their structural features. Whereas the QSAR study gave relatively low correlations, the CoMFA study gave a correlation with high predictive value.

Animals↗
PubMed1991

Isothiocyanate derivatives of cocaine: irreversible inhibition of ligand binding at the dopamine transporter.

Isothiocyanate derivatives of (-)-cocaine were prepared and tested for inhibitory potency at the cocaine receptor in rat striatal membranes. Coincubation with m-isothiocyanatobenzoylecgonine methyl ester (m-ISOCOC), p-isothiocyanatobenzoylecgonine methyl ester (p-ISOCOC), and 3 beta-(4-isothiocyanatophenyl)tropane-2-carboxylic acid methyl ester (ISOWIN) resulted in inhibition of [3H]WIN 35,428 binding, but the compounds were about 10-fold weaker than (-)-cocaine. However, p-ISOCOC was approximately 3-fold more potent than metaphit, an isothiocyanate derivative of phencyclidine. p-ISOCOC was equipotent at the serotonin transporter but was much less potent at the norepinephrine transporter and was inactive at the D2 dopamine receptor at 1000 microM concentration. The IC50 value for m-ISOCOC and p-ISOCOC varied with tissue concentration, suggesting irreversible inhibition of binding. Preincubation with m-ISOCOC and p-ISOCOC resulted in inhibition of [3H]WIN 35,428 binding that could not be removed by washing of the membranes; in contrast, preincubation with (-)-cocaine caused inhibition that was readily removed by washing. Preincubation with 1 microM concentrations of p-ISOCOC resulted in a large reduction in Bmax of the high affinity binding site for [3H]WIN 35,428. Preincubation with 100 microM p-ISOCOC eliminated the high affinity site and apparently reduced the affinity at the low affinity site. Coincubation of 10 microM p-ISOCOC with 100 microM cocaine prevented the total loss of [3H]WIN 35,428 binding. The uptake of [3H]dopamine was inhibited by p-ISOCOC with an IC50 comparable to that of cocaine. Additionally, preincubation of rat striatal synaptosomes with 10 microM p-ISOCOC reduced the Vmax of [3H]dopamine uptake after washing. These data suggest that m-ISOCOC and p-ISOCOC are useful irreversible acylators of (-)-cocaine binding sites at the dopamine transporter.

Animals↗
PubMed1991

BMY 30047: a novel topically active retinoid with low local and systemic toxicity.

In the treatment of various dermatological disorders, topically applied retinoids have potential therapeutic use with the advantage of improved localized activity and lower toxicity over systemically administered retinoids. However, most retinoids cause a significant degree of local irritation. In the present study, the ability to produce local activity with low local irritation potential was evaluated with a novel retinoic acid derivative. BMY 30047 (11-cis, 13-cis-12-hydroxymethylretinoic acid delta-lactone) is one of a series of retinoic acid derivatives in which the carboxyl function of the polar end was modified with the aim of achieving reduced local irritation and systemic toxicity while retaining the local therapeutic effect. BMY 30047 was evaluated and compared with all-trans retinoic acid for topical retinoid activity in several preclinical assay systems, including the utricle reduction assay in rhino mice, 12-o-tetradecanoylphorbol 13-acetate ester-stimulated ornithine decarboxylase induction in hairless mice and the UV light-induced photodamaged skin model in hairless mice. BMY 30047 was assessed for retinoid-type side effects by evaluating the skin irritation potential in rabbits after repeated topical application, and hypervitaminosis A-inducing potential in mice after i.p. injection. BMY 30047 demonstrated significant topical retinoid activity in several in vivo models with less skin irritation potential relative to the most used clinical concentrations of all-trans retinoic acid. BMY 30047 also showed very little systemic activity and did not produce any evidence of hypervitaminosis A syndrome at systemic doses 20 times greater than the no-effect dose of all-trans retinoic acid.

Administration, Topical↗
PubMed1990

New, potent cocaine analogs: ligand binding and transport studies in rat striatum.

Two potent cocaine analogs have been developed that have the highest known affinities for the cocaine binding site in rat striatum. Both 3 beta-(4-chlorophenyl)- (RTI-COC-31) and 3 beta-(4-methylphenyl)-tropane-2-carboxylic acid methyl ester (RTI-COC-32) compete for [3H]WIN 35,428 and [3H]mazindol binding with a IC50 that is 100 times more potent than that of (-) cocaine. Additionally, these compounds inhibit [3H]dopamine uptake with a similar, high potency. These results may lead to the development of high affinity probes for the cocaine binding site.

Animals↗
PubMed1989

Blockade of N-methyl-D-aspartate induced convulsions by 1-aminocyclopropanecarboxylates.

1-Aminocyclopropanecarboxylic acid is a potent and selective ligand for the glycine modulatory site on the N-methyl-D-aspartate receptor complex. This compound blocks (ED50 234 mg/kg) the convulsions and deaths produced by N-methyl-D-aspartate (125 mg/kg) in a dose dependent fashion. In contrast, 1-aminocyclopropanecarboxylic acid does not protect mice against convulsions induced by pentylenetetrazole (80 mg/kg), strychnine (2 mg/kg), bicuculline (6 mg/kg), or maximal electroshock (50 mA, 0.2 s), and does not impair motor performance on either a rotarod or horizontal wire at doses of up to 2 g/kg. The methyl- and ethyl- esters of 1-aminocyclopropanecarboxylic acid are 5- and 2.3-fold more potent, respectively, than the parent compound in blocking the convulsant and lethal effects of N-methyl-D-aspartate. However, these esters are several orders of magnitude less potent (IC50 greater than 40 microM) than 1-aminocyclopropanecarboxylic acid as inhibitors of strychnine-insensitive [3H] glycine binding, indicating that conversion to the parent compound may be required to elicit an anticonvulsant action. These findings suggest that 1-aminocyclopropanecarboxylates may be useful in the treatment of neuropathologies associated with excessive activation of N-methyl-D-aspartate receptor coupled cation channels.

Amino Acids↗
PubMed1989

1-Aminocyclopropane carboxylic acid: a potent and selective ligand for the glycine modulatory site of the N-methyl-D-aspartate receptor complex.

1-Aminocyclopropane carboxylic acid (ACPC) competitively inhibited (IC50, 38 +/- 7 nM) [3H]glycine binding to rat forebrain membranes but did not affect [3H]strychnine binding to rat brainstem/spinal cord membranes. Like glycine, ACPC enhanced 3H-labelled (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate ([3H]MK-801) binding to N-methyl-D-aspartate receptor-coupled cation channels (EC50, 135 +/- 76 nM and 206 +/- 78 nM for ACPC and glycine, respectively) but was approximately 40% less efficacious in this regard. The maximum increase in [3H]MK-801 binding produced by a combination of ACPC and glycine was not different from that elicited by glycine, but both compounds potentiated glutamate-stimulated [3H]MK-801 binding. These findings indicate that ACPC is a potent and selective ligand at the glycine modulatory site associated with the N-methyl-D-aspartate receptor complex.

Amino Acids↗
PubMed1989

meta- and para-isothiocyanato-t-butylbicycloorthobenzoate: irreversible ligands of the gamma-aminobutyric acid-regulated chloride ionophore.

The meta- and para-isothiocyanato derivatives of t-butylbicycloorthobenzoate (TBOB) were synthesized by catalytic reduction of the corresponding nitro compounds, followed by treatment with thiophosgene. p-NCS-TBOB (2) inhibited the binding of both [3H]TBOB and [35S]t-butylbicyclophosphorothionate (TBPS) with potencies (IC50 of 61 and 23 nM, respectively) similar to the parent compound. In contrast, the meta derivative (m-NCS-TBOB, 1) was more than 1 order of magnitude less potent (IC50 of 1588 and 149 nM, respectively). The IC50 values for both 1 and 2 were strongly dependent on the tissue concentration, in a manner characteristic of irreversible inhibitors. Moreover, preincubation of tissue with these compounds, followed by extensive washing, resulted in a concentration-dependent reduction in the number of [35S]TBPS binding sites and in the apparent affinity of this radioligand. Similar effects were not observed in tissues treated in identical fashion with either TBOB or picrotoxin. Preincubation with p-NCS-TBOB at concentrations that significantly inhibit [35S]TBPS or [3H]TBOB binding did not affect radioligand binding to either benzodiazepine or gamma-aminobutyric acid receptors. These findings suggest that m- and p-NCS-TBOB bind irreversibly to sites labeled by cage convulsants such as TBOB and TBPS, which are on or near GABA-gated chloride channels. p-NCS-TBOB should prove useful in determining the molecular characteristics of the benzodiazepine receptor-coupled GABA-gated chloride ionophore.

Animals↗
PubMed1984

Solution conformations of barbituric acid derivatives: a 3J(13C,1H) NMR study.

The conformations of the 5-alkyl chains of 5,5-dialkylbarbituric acid derivatives in polar and nonpolar media were determined from the magnitudes of the vicinal heteronuclear coupling constants between the alpha-alkyl hydrogens and the carbonyl carbons. The experimental 3J values have been compared to theoretical values, and the conformational populations of the alkyl side chains with respect to the trioxopyrimidine ring have been determined. The results show that all these compounds have a very low barrier to rotation for both butyl and ethyl side chains. The barbiturates that do not have a 1'-methyl group in the butyl side chain, butobarbital and amobarbital, have no preferred conformation for either the butyl or ethyl side chains. However, the compounds with a 1'-methyl group, pentobarbital and alpha-methylamobarbital, exhibit preferred conformation for both alkyl chains. The significance of these results to the relationship between conformations and pharmacological activity is discussed.

Barbiturates↗
PubMed1980

Positive identification and quantitation of isomeric cocaines by high-performance liquid chromatography.

A high-performance liquid chromatographic procedure for separating and identifying the four isomeric cocaines has been developed. Use of this procedure with an internal standard allows for the determination of the quantity of any isomeric cocaine in an unknown sample. The pitfalls and problems encountered in the use of gas chromatography and mass spectrometry in the analysis of cocaines and ecgonine methyl esters are discussed.

Chromatography, High Pressure Liquid↗