Search PubMed⌕ Search

Biomedical subjects

J L Neumeyer

Publications and source records attributed to J L Neumeyer.

At least 73 records · Page 4Linked to original sources
PubMed1990

N-modified fluorophenyltropane analogs of cocaine with high affinity for cocaine receptors.

The binding properties of three N-modified fluorophenyltropane analogs of cocaine were compared in competition experiments with [3H]cocaine. All three analogs displaced specifically bound [3H]cocaine from caudate-putamen membranes of cynomolgus monkeys with affinities exceeding that of cocaine. The compound with the highest affinity, 2 beta-carbomethoxy-3 beta-(4-fluorophenyl)-N-allyl-nortropane, (N-allyl-CFNT) was about three times more potent than cocaine. N-Allyl-CFNT also had cocaine-like interoceptive effects and was about three times more potent than cocaine in squirrel monkeys trained to discriminate cocaine from vehicle in an operant drug discrimination procedure. The results suggest that N-modified fluorophenyltropane derivatives may be useful precursors for development of pharmacological probes for cocaine receptors.

Animals↗
PubMed1990

Synthesis and structural requirements of N-substituted norapomorphines for affinity and activity at dopamine D-1, D-2, and agonist receptor sites in rat brain.

A series of N-substituted analogues of (R)-(-)-norapomorphine were synthesized to study the optimal structural requirements of the N-alkyl side chain to interact with D-1 and D-2 dopaminergic receptors as well as dopamine (DA) agonist binding sites. Evaluations included testing the affinity of these compounds for DA receptor sites in rat striatal tissue and assessing stereotypy as a behavioral index of dopaminergic activity. The electronic, steric, and lipophilic properties of the N-alkyl side chain were found to be related to affinity, D-2 selectivity, and dopaminergic activity. All 11 compounds evaluated had relatively low affinity at D-1 sites. Optimum D-2 and agonist-site affinity as well as agonist activity were exhibited by N-cyclopropylmethyl (7) greater than or equal to N-allyl (8) greater than or equal to N-propyl (4) or N-ethyl (3) substituted compounds. Branching of the N-alkyl side chain as in N-isopropyl (5) and N-isobutyl (6) markedly reduced the D-2 affinity and activity, presumably due to steric effects. The N-trifluoroethyl (10) and N-pentafluoropropyl (11) derivatives had low affinity for all their dopamine receptor sites and no agonistic activity; evidently, the highly electronegative F atoms decrease basicity of the N atom and therefore decrease the ability of the N atom to be cationic at physiological pH, a proposed requirement for high-affinity binding to DA receptors.

Animals↗
PubMed1990

Development of a high affinity and stereoselective photoaffinity label for the D-1 dopamine receptor: synthesis and resolution of 7-[125I]iodo-8-hydroxy-3-methyl-1-(4'-azidophenyl)-2,3,4,5-tetrahydro- 1H-3-benzazepine.

In an earlier paper, we reported the development of (+-)-7-iodo-8-hydroxy-3-methyl-1-(4'-azidophenyl)-2,3,4,5-tetrahydro- 1H-3-benzazepine (I-MAB) and its 125I analogue ([125I]I-MAB) as selective, high affinity photoaffinity labels for the D-1 dopamine receptor. In this report, we now describe the complete synthesis and resolution of I-MAB and the pharmacological characterization of the stereoisomers in canine striatal membranes. R-(+)-I-MAB showed highly specific dopamine D-1 receptor binding (KD = 0.28 nM) and binds selectively and stereoselectively to the D-1 receptor. These results further confirm the previous suggestion that, in the benzazepine series of DA agonists and antagonists, the activity principally resides in the R-(+) enantiomer, the S-(-) enantiomer being considerably less potent or inactive. Moreover, R-(+)-[125I]I-MAB, upon photolysis, identifies the ligand-binding subunits of the neuronal D-1 receptor, with an apparent Mr of 74,000, 62,000, and 51,000 as assessed by autoradiography following sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Photoincorporation of R-(+)-[125I]I-MAB into these polypeptides was stereoselectively blocked by D-1 dopaminergic ligands with an appropriate pharmacologic profile for the receptor. R-(+)-[125I]I-MAB should thus prove to be a useful stereoselective photoaffinity label for the further characterization of the D-1 receptors.

Affinity Labels↗
PubMed1990

Synthesis and dopamine receptor affinities of enantiomers of 2-substituted apomorphines and their N-n-propyl analogues.

Syntheses of (R)-(-)-2-methoxyapomorphine (R-8), its antipode S-8, and its (R)-(-)-N-n-propyl R-9 derivatives are described. The dopaminergic receptor affinities of these compounds and their 2-unsubstituted counterparts (R)-(-)-apomorphine (R(-)-APO, R-1), (S)-(+)-apomorphine (S(+)-APO, S-1), and (R)-(-)-N-n-propylnorapomorphine (R(-)-NPA, R-2), as well as those of (R)-(-)-2-chloroapomorphine (R(-)-2-Cl-APO, R-6), (R)-(-)-2-bromoapomorphine (R(-)-2-Br-APO, R-6), were determined with tissue membrane preparations of corpus striatum from rat brain. Contribution of both an N-n-propyl and a 2-hydroxy in (R)-(-)-2-hydroxy-N-n-propylnorapomorphine (R(-)-2-OH-NPA, R-7) or a methoxy group in (R)-(-)-2-methoxy-N-n-propylnorapomorphine (R(-)-2-OCH3-NPA, R-9) produced the highest D2 affinity (0.053 and 0.17 nM) and D2 over D1 selectivity (17,300 and 10,500 times) of the compounds evaluated. The structure-affinity relationships of these 2-substituted aporphines suggest that secondary binding sites of D2 receptors interact with 2-substituents on the A ring of aporphines through H-bonding.

Animals↗
PubMed1990

Presynaptic inhibition of dopamine synthesis in rat striatal tissue by enantiomeric mono- and dihydroxyaporphines.

Presynaptic autoreceptor-mediated modulation of dopamine (DA) synthesis was evaluated as the inhibition of tyrosine hydroxylase activity by enantiomeric mono- and dihydroxyaporphines with minced striatal tissue from rat brain. The isomers of N-n-propylnorapomorphine (NPA) both inhibited tyrosine hydroxylase activity [IC50 = 0.3 and 1.0 microM for (R)-(-)- and (S)-(+)-NPA, respectively; R/S potency = 3.6]. Their effects were fully blocked by the nonselective DA receptor antagonist fluphenazine, as well as by the D2-selective antagonist spiperone, but not by the D1 antagonist SCH-23390. These results suggest a D2-type autoreceptor-mediated inhibition of DA synthesis, with limited enantiomeric selectivity of this catechol-aporphine. The corresponding monohydroxy analogs, (R)-(-)- and (S)-(+)-11-hydroxy-N-n-propylnoraporphine (11-OH-NPa) were about 100 times less potent (IC50 = 42 and 87 microM, respectively) than the NPA isomers in fully inhibiting the enzyme activity in normal tissue but, after depletion of endogenous DA by acute in vivo pretreatment with reserpine (which did not alter the number of D1 or D2 specific binding sites), (R)-(-)-11-OH-NPa was a highly potent but partial agonist (IC25 = 7 nM). Fluphenazine and spiperone fully antagonized the inhibition of tyrosine hydroxylase by (R)-(-)-11-OH-NPa in reserpinized tissue, but SCH-23390 was ineffective. Actions mediated by endogenous DA probably contribute to the effect of high concentrations of (R)-(-)-11-Oh-NPa to evoke a full inhibition of DA synthesis, but its high potency partial agonist effects appear to be mediated by D2-autoreceptors. (S)-(+)-11-OH-NPa was a very weak partial agonist in reserpinized tissue, with an IC25 = 30 microM (essentially the same as normal tissue); thus, (R)-(-)-11-OH-NPa was greater than 4,000 times more potent than its S-(+)-enantiomer in the absence of endogenous DA. These results demonstrate that NPA, which contains a catechol moiety, acts as a full agonist to inhibit striatal DA synthesis via a presynaptic autoreceptor of the D2 type, with only slight stereoselectivity, and that its monohydroxy analog is a very potent but partial D2 autoreceptor agonist, with very high stereoselectivity.

Animals↗
PubMed1990

Fluorescent and biotin probes for dopamine receptors: D1 and D2 receptor affinity and selectivity.

Fluorophor and biotin derivatives of dopamine agonist and antagonist drugs were synthesized and evaluated for binding affinity and selectivity at D1 and D2 dopamine receptors in membranes prepared from monkey (Macaca fascicularis) caudate putamen. Binding was measured using [3H]SCH 23390 to label D1 receptors and [3H]spiperone to label D2 receptors. The selective D1 antagonist SKF 83566, whether coupled to 7-nitrobenz-2-oxa-1,3-diazole-4-yl (NBD), to fluorescein, or to biotin retained high affinity for D1 dopamine receptors (Ki, 5.3 16 and 3.5 nM, respectively) and high D1/D2 receptor selectivity (130-, 300, and 600-fold, respectively). The selective D2 antagonist derivative N-(p-aminophenethyl)spiperone, (NAPS) coupled either to biotin or to NBD via the N-aminoethylphenyl group, likewise retained high D2 receptor affinity (Ki, 0.58 and 0.66 nM, respectively) and high D2/D1 selectivity (190- and 150-fold, respectively). The affinity of the NBD-coupled derivative of (S)-2-(N-phenylethyl-N-propyl)-amino-5-hydroxytetralin hydrochloride [(S)-PPHT], a selective D2 agonist, was actually higher than that of the parent compound (Ki, 0.30 versus 2.1 nM), whereas the affinity of fluorescein-coupled (S)-PPHT was lower (Ki, 4.8 nM). Sensitivity to GTP, a characteristic of agonist binding at dopamine receptors, was demonstrated for NBD-coupled (S)-PPHT, because D2 receptor affinity was somewhat reduced in the presence of GTP. PPHT-fluorescein fluorescence labeling rimmed cells in monkey and rat anterior pituitary and outlined cells in the striatum. Fluorescent and biotin probes based on selective high affinity ligands for dopamine receptors may expedite studies of receptor localization and mobility at the cellular level.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1989

2-Haloaporphines as potent dopamine agonists.

The synthesis of 2-amino- and 2-halo-substituted aporphines is described. The key step is the substitution of a hydroxy group in the 2-position with an amino group effected by a Smiles rearrangement reaction of the 2-methylpropanamide derivative 6. The affinity of the new compounds for the dopamine D-2 receptor in the anterior pituitary gland was evaluated. 2-Fluoroapomorphine was the most potent compound, being 1.5 times more potent than (-)-apomorphine. The structure-activity relationships are discussed in relation to a previously proposed receptor model.

Animals↗
PubMed1989

Sulfur-containing 1,3-dialkylxanthine derivatives as selective antagonists at A1-adenosine receptors.

Sulfur-containing analogues of 8-substituted xanthines were prepared in an effort to increase selectivity or potency as antagonists at adenosine receptors. Either cyclopentyl or various aryl substituents were utilized at the 8-position, because of the association of these groups with high potency at A1-adenosine receptors. Sulfur was incorporated on the purine ring at positions 2 and/or 6, in the 8-position substituent in the form of 2- or 3-thienyl groups, or via thienyl groups separated from an 8-aryl substituent through an amide-containing chain. The feasibility of using the thienyl group as a prosthetic group for selective iodination via its Hg2+ derivative was explored. Receptor selectivity was determined in binding assays using membrane homogenates from rat cortex [( 3H]-N6-(phenylisopropyl)adenosine as radioligand] or striatum [3H]-5'-(N-ethylcarbamoyl)adenosine as radioligand] for A1- and A2-adenosine receptors, respectively. Generally, 2-thio-8-cycloalkylxanthines were at least as A1 selective as the corresponding oxygen analogue. 2-Thio-8-aryl derivatives tended to be more potent at A2 receptors than the oxygen analogue. 8-[4-[(Carboxy-methyl)oxyl] phenyl]-1,3-dipropyl-2-thioxanthine ethyl ester was greater than 740-fold A1 selective.

Animals↗
PubMed1989

Cocaine receptors labeled by [3H]2 beta-carbomethoxy-3 beta-(4-fluorophenyl)tropane.

The potent cocaine analog 2 beta-carbomethoxy-3 beta-(4-fluorophenyl)-tropane (CFT, also designated WIN 35,428) was tritiated and evaluated as a molecular probe for cocaine receptors in caudate putamen membranes of cynomolgus monkeys. Kinetic, saturation, and competition experiments indicated that [3H]CFT, like [3H]cocaine, bound to at least two components. Association and dissociation of the radioligand at 0-4 degrees occurred in two phases; the t 1/2 for dissociation of the fast and slow components was 2.5 and 23 min, respectively. Saturation analysis revealed high and low affinity binding components with affinities (Kd) of 4.7 +/- 1.2 and 60 +/- 12 nM (means +/- SE) and densities (Bmax) of 50 +/- 18 and 290 +/- 20 pmol/g of tissue, respectively. [3H]CFT was displaced stereoselectively by the enantiomers of cocaine and by the diastereoisomers of the phenyltropane analog of cocaine. Most congeners displaced [3H]CFT fully, with shallow competition curves (nH, 0.69-0.81). In contrast, several monoamine uptake inhibitors structurally unrelated to cocaine (GBR 12909, Lu 19-005, and mazindol) displaced a maximum of about 90% specifically bound [3H]CFT, with steeper competition curves (nH, 0.89-1.3), suggesting that these drugs bind to a subpopulation of [3H]CFT-labeled sites. The rank order of potency observed in the present study is identical to the rank order of potency at binding sites labeled by [3H]cocaine: Lu 19-005 greater than mazindol greater than CFT greater than GBR 12909 greater than (-)-cocaine greater than bupropion greater than WIN 35,140 greater than (+)-cocaine. Moreover, there is a high positive correlation (r, 0.99, p less than 0.001) between the affinities of drugs at sites labeled by [3H]CFT and [3H]cocaine. The results show that [3H]CFT and [3H]cocaine bind to a similar spectrum of sites in monkey caudate putamen. Because of its higher affinity and slower dissociation rate, [3H]CFT appears to be a superior radioligand probe for these sites.

Animals↗
PubMed1988

Determination of N-n-propylnorapomorphine in serum and brain tissue by gas chromatography-negative ion chemical ionization mass spectrometry.

A method for the determination of the neuroactive compound N-n-propylnorapomorphine (NPA) in biological tissues is described. Isolation of NPA from serum or brain tissue was achieved via liquid-liquid extraction from phosphate-buffered tissue extract (0.25 M, pH 7.2) into ethyl acetate. The NPA, along with a [2H7]NPA analogue serving as internal standard, was converted to the corresponding bis(trifluoroacetyl) ester by treatment with excess trifluoroacetic anhydride at 75 degrees C. The electrophoric derivatives were analyzed by fused-silica capillary gas chromatography-mass spectrometry in the negative ion chemical ionization mode. Selected ion monitoring of the [M-CF3CO]- ions of derivatized NPA (m/z 390) and internal standard [2H7]NPA (m/z 397) permitted the quantitation of NPA in serum and brain samples obtained from rats treated with either free NPA or the prodrug methylenedioxy-NPA (MDO-NPA). Calibration was conducted down to a practical limit of assay sensitivity, at 0.50 ng NPA per ml of serum and 0.50 ng NPA per g of brain. The relative standard deviation for replicate serum samples spiked at 20 ng/ml was 4.2% (n = 5) and for brain samples at 10 ng/g, it was 3.6%. This method revealed differences in the free NPA brain/serum ratios in rats treated separately with the stereoisomers R-(-)-MDO-NPA and S-(+)-MDO-NPA.

Animals↗
PubMed1988

Photoaffinity labeling of dopamine D1 receptors.

A high-affinity radioiodinated D1 receptor photoaffinity probe, (+/-)-7-[125I]iodo-8-hydroxy-3-methyl-1-(4-azidophenyl)-2,3,4,5-tetra hyd ro- 1H-3-benzazepine ([125I]IMAB), has been synthesized and characterized. In the absence of light, [125I]IMAB bound in a saturable and reversible manner to sites in canine brain striatal membranes with high affinity (KD approximately equal to 220 pM). The binding of [125I]IMAB was stereoselectively and competitively inhibited by dopaminergic agonists and antagonists with an appropriate pharmacological specificity for D1 receptors. The ligand binding subunit of the dopamine D1 receptor was visualized by autoradiography following photoaffinity labeling with [125I]IMAB and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Upon photolysis, [125I]IMAB incorporated into a protein of apparent agents in a stereoselective manner with a potency order typical of dopamine D1 receptors. In addition, smaller subunits of apparent Mr 62,000 and 51,000 were also specifically labeled by [125I]IMAB in these species. Photoaffinity labeling in the absence or presence of multiple protease inhibitors did not alter the migration pattern of [125I]IMAB-labeled subunits upon denaturing electrophoresis in both the absence or presence of urea or thiol reducing/oxidizing reagents. [125I]IMAB should prove to be a useful tool for the subsequent molecular characterization of the D1 receptor from various sources and under differing pathophysiological states.

Affinity Labels↗
PubMed1988

8-Substituted xanthines as antagonists at A1- and A2-adenosine receptors.

Two classes of 8-substituted analogs of theophylline (1,3-dialkylxanthines), having 8-cycloalkyl, 8-cycloalkenyl or 8-(para-substituted aryl) groups, were shown to be potent and, in some cases, receptor subtype selective antagonists at A1- and A2-adenosine receptors. New analogs based on a functionalized cogener approach and on classical medicinal chemical approaches were prepared. Affinity at A1-adenosine receptors was evaluated by inhibition of binding of [3H]N6-phenylisopropyladenosine to rat brain membranes. Activity at A2-adenosine receptors was measured by the reversal of 5'-N-ethylcarboxamidoadenosine (NECA)-stimulated production of cyclic AMP in membranes from rat pheochromocytoma PC12 cells. Cycloalkenyl analogs containing rigid olefinic bonds differed greatly in potency from the saturated analogs. The selectivity of phenylsulfonamide analogs depended on distal structural features. Novel xanthine analogs include diamino-, thiol-, aldehyde, and halogen-substituted derivatives, peptide conjugates of 8-[4-[2-aminoethylaminocarbonylmethyloxy]phenyl]1,3-dipropylxan thi ne (XAC), and a hydroxyethylamide analog of XAC.

Adenosine↗
PubMed1988

High-performance liquid chromatographic separation and electrochemical or spectrophotometric determination of R(-)N-n-propylnorapomorphine and R(-)10,11-methylenedioxy-N-n-propylnoraporphine in primate plasma.

The dopamine receptor agonist R(-)N-n-propylnorapomorphine (NPA) and its proposed pro-drug R(-)10,11-methylenedioxy-N-n-propylnoraporphine (MDO-NPA) were isolated simultaneously from monkey plasma using a solid-phase extraction procedure. R(-)Apomorphine (APO) and R(-)10,11-methylenedioxyaporphine (MDO-APO) were added as internal standards, and separation and quantification were by high-performance liquid chromatography with electrochemical or ultraviolet detection of the free catechol and MDO compounds, respectively. The detection limits for NPA and MDO-NPA in plasma were 0.5 and 10 ng/ml and the coefficient of variation (S.D./mean) within assays and between days of assays for both drugs was 5.6% or less. Quantification of plasma levels of NPA and MDO-NPA was possible at ranges of 2-1000 and 40-5000 ng/ml, respectively, including concentrations found after intravenous administration of these agents.

Animals↗
PubMed1988

Synthesis and dopamine agonist and antagonist effects of (R)-(-)- and (S)-(+)-11-hydroxy-N-n-propylnoraporphine.

The R-(-) and S-(+) enantiomers of 11-hydroxy-N-n-propylnoraporphine, (R)-3 and (S)-3, were synthesized in six steps from 1-(3-methoxy-2-nitrobenzyl)isoquinoline. Neuropharmacological evaluation of the R and S isomers (by affinity to dopamine receptor sites in rat brain tissues, induction of stereotyped behavior, and interaction with motor arousal induced by (R)-apomorphine in the rat) indicated that, similar to the 10,11-dihydroxy congener 2, both enantiomers can bind to dopamine receptors but that only (R)-3 activates them, whereas (S)-3 shows activity as a dopaminergic antagonist.

Animals↗