Andrew Thurkauf

Synthesis and evaluation of optically pure [3H]-(+)-pentazocine, a highly potent and selective radioligand for σ receptors

Tritium‐labeled (+)‐pentazocine ([3H]‐1b) of specific activity 26.6 Ci/mmol was synthesized in 3 steps starting with (+)‐normetazocine (2) of defined optical purity. [3H]‐1b has been characterized as a highly selective ligand for labeling of σ receptors. Competition data revealed that [3H]‐1b could be displaced from guinea pig brain membrane preparations with a number of commonly used σ receptor ligands. [3H]‐1b exhibited saturable, enantioselective binding with a K d of 5.13±0.97 nM and a B max of 1146±122 fmol/mg protein. Phencyclidine (PCP) displaced [3H]‐1b with low affinity while MK‐801 was inactive, thus indicating insignificant activity at the PCP‐binding site; apomorphine failed to displace [3H]‐1b indicating lack of dopamine receptor cross‐reactivity. Since the affinity of [3H]‐1b is about 6 times that of the two commonly employed σ ligands ((+)‐3‐[3H]PPP and [3H]DTG) and since it is more selective for σ receptors than the benzomorphan [3H]SKF‐10,047, it represents the first example of a highly selective benzomorphan based σ receptor ligand. [3H]‐1b should prove useful for further study of the structure and function of σ receptors.

GBR12909 antagonizes the ability of cocaine to elevate extracellular levels of dopamine

Rats were administered various IP doses of the high-affinity dopamine (DA) reuptake inhibitor 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-[3-phenylpropyl]piperazine (GBR12909). The caudate nuclei were removed 60 min after drug administration and stored at -70 degrees C. Striatal membranes were prepared later. The results demonstrated that GBR12909 produced a dose-dependent decrease in the binding of [3H]cocaine or [3H]GBR12935 to the DA transporter (ED50 about 10 mg/kg). Saturation binding studies with [3H]GBR12935 showed that this was due to both an increase in the Kd, due to residual drug, and to a decrease in the Bmax. At a dose of 25 mg/kg IP, GBR12909 produced a 50% decrease in the Bmax, and a 3.4-fold increase in the Kd. In the in vivo microdialysis studies, GBR12909 (25 mg/kg IP) produced a modest, long-lasting and stable elevation of extracellular DA. Administration of cocaine through the microdialysis probe to rats pretreated with either saline or GBR12909 (25 mg/kg IP) produced a dose-dependent increase in extracellular DA in both groups. GBR12909 inhibited cocaine-induced increases in extracellular DA by about 50% at all doses. These data collectively indicate that at a dose sufficient to decrease by 50% the Bmax of [3H]GBR12935 binding sites, GBR12909 antagonizes the ability of cocaine to elevate extracellular DA by 50%. Further studies will be needed to evaluate a possible role for GBR12909 in the medical treatment of cocaine addiction.

NGB 2904 and NGB 2849: two highly selective dopamine D3 receptor antagonists.

N-(4-[4-¿2, 3-dichlorophenyl¿-1-piperazinyl]butyl)-3-fluorenylcarboxamide and N-(4-[4-¿2, 3-dichlorophenyl¿-1-piperazinyl]butyl)-2-biphenylenylcarboxamide were prepared in several steps from 2,3-dichloroaniline. These compounds were identified as highly selective dopamine D3 receptor antagonists.

Tight binding dopamine reuptake inhibitors as cocaine antagonists: a strategy for drug development

The experiments reported in this study tested the hypothesis that tight binding dopamine (DA) reuptake inhibitors might act as cocaine antagonists. Binding studies demonstrated that the high affinity dopamine reuptake inhibitor, 1‐[2‐[bis(4‐fluorophenyl)methoxy]ethyl]‐4‐[3‐phenylpropyl]piperazine (GBR12909) produced a wash‐resistant inhibition of the DA transporter in rat striatal membranes as labeled by [3H]cocaine or [3H]1‐[2‐(diphenyl‐methoxy)ethyl]‐4‐(3‐phenylpropyl)piperazine ([3H]GBR12935), indicative of tight binding. In vivo microdialysis experiments showed that administration of 25 GBR12909 to rats produced a modest, but not statistically significant, increase in the extracellular levels of striatal DA, while this same dose of GBR12909 inhibited the ability of cocaine to elevate extracellular DA levels by 64%. These data suggest that tight binding DA reuptake blockers may provide a fruitful approach for developing a cocaine antagonist.

Indoline and piperazine containing derivatives as a novel class of mixed D2/D4 receptor antagonists. Part 2: Asymmetric synthesis and biological evaluation

A series of chiral benzylpiperazinyl-1-(2,3-dihydro-indol-1-yl)ethanone derivatives were prepared and examined for their affinity at dopamine D(2) and D(4) receptors. Three compounds having D(2)/D(4) affinity ratios approximating that found for the atypical neuroleptic clozapine were further evaluated in behavioral tests of antipsychotic efficacy and motor side effects.

Indoline and piperazine containing derivatives as a novel class of mixed D2/D4 receptor antagonists. Part 1: Identification and structure–activity relationships

Optimization of the lead compound 2-[-4-(4-chloro-benzyl)-piperazin-1-yl]-1-(2,3-dihydro-indol-1-yl)-ethanone 1 by systematic structure-activity relation (SAR) studies lead to two potent compounds 2-[-4-(4-chloro-benzyl)-piperazin-1-yl]-1-(2-methy-2,3-dihydro-indol-1-yl)-ethanone 2n and 2-[-4-(4-chloro-benzyl)-piperazin-1-yl]-1-(2-methy-2,3-dihydro-indol-1-yl)-ethanone 7b. Their related synthesis was also reported.

Design, synthesis, and discovery of 3-piperazinyl-3,4-dihydro-2(1H)-quinolinone derivatives: a novel series of mixed dopamine D2/D4 receptor antagonists

3-Piperazinyl-3,4-dihydro-2(1H)-quinolinone derivatives (delta-lactams) were designed, synthesized, and identified as a new series of mixed dopamine D2/D4 receptor antagonists. To further the structure-activity relationship (SAR) study, 3-piperazinylindolin-2-ones (gamma-lactams) and 3-piperazinyl-3H,4H,5H-benzo[f]azepin-2-ones (epsilon-lactams) were also prepared and examined.

Comparison of the effects of the acute administration of dexoxadrol, levoxadrol, MK-801 and phencyclidine on body temperature in the rat

Some of the dioxolanes produce pharmacological effects that have much in common with phencyclidine and phencyclidine-like drugs. Dioxadrol can be resolved into two enantiomers, dexoxadrol and levoxadrol. Dexoxadrol has an affinity for phencyclidine receptors that is much greater than that of levoxadrol, but dexoxadrol and levoxadrol have nearly equal affinities for sigma receptors. The systematic analysis of the relative potencies of dexoxadrol and levoxadrol can be used as an approach to define effects mediated by phencyclidine vs sigma receptors. Compounds that act on phencyclidine receptors, as well as affecting behavior, alter body temperature in the rat. The purpose of the present study was to compare and contrast the effects of the acute administration of dexoxadrol, levoxadrol, MK-801 and phencyclidine on body temperature in the rat. Dexoxadrol and levoxadrol (5.0, 10.0, 20.0 or 40.0 mg/kg), MK-801 (0.12, 0.6 or 1.2 mg/kg) or phencyclidine (5.0, 10.0 or 20.0 mg/kg) were administered subcutaneously and body temperature was measured. Both dexoxadrol and MK-801 produced hyperthermia but levoxadrol did not affect body temperature. In contrast to the hyperthermic effects of dexoxadrol and MK-801, phencyclidine produced hypothermia. These findings indicate that hypothermia induced by phencyclidine is not due to interactions with phencyclidine receptors and, while dexoxadrol, MK-801 and phencyclidine may share some similar receptor binding and behavioral characteristics, they can be differentiated on the basis of their effects on body temperature.

MK-801 ameliorates delayed amnesia, but potentiates acute amnesia induced by CO.

The effects of non-competitive N-methyl-D-aspartate receptor antagonists on amnesia induced by carbon monoxide (CO) were investigated, since they have neuroprotective effects on delayed degeneration induced by ischemia. In the mice exposed to CO, acute and delayed amnesia were induced. (+)-MK-801 and (-)-MK-801 improved the delayed amnesia, but the effects of phencyclidine (PCP) were weak. (+)-MK-801 and PCP potentiated the acute amnesia. From these results, it is suggested that there is a stereoselectivity in the effects of MK-801 on CO-induced amnesia and that CO-induced delayed amnesia animals could be used as an ischemic amnesia model.

Atypical antipsychotic-like effects of the dopamine D3 receptor agonist, (+)-PD 128,907

Anti-schizophrenia agents with improved efficacy and side-effect profiles are required. A dopamine D3 receptor agonist, R-(+)-trans-3,4a,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano[4,3- b]-1,4-oxazin-9-ol HCl ((+)-PD 128,907), displayed an atypical antipsychotic profile comparable to that of clozapine. (+)-PD 128,907 blocked stereotypy produced by dizocilpine (MK-801) at 12-fold lower doses than those affecting apomorphine-induced stereotypes in mice and did not produce catalepsy. These effects of (+)-PD 128,907 were stereospecific and were blocked by a D3 antagonist. These data suggest a role for D3 receptors in antipsychotic drug action.