Novel Heterocyclic Trans Olefin Analogues of N-{4-[4-(2,3-Dichlorophenyl)piperazin-1-yl]butyl}arylcarboxamides as Selective Probes with High Affinity for the Dopamine D3 Receptor

Abstract

Dopamine D3 receptor subtypes have been hypothesized to play a pivotal role in modulating the reinforcing and drug-seeking effects induced by cocaine. However, definitive pharmacological investigations have been hampered by the lack of highly D3 receptor selective compounds that can be used in vivo. To address this problem, the potent and D3-receptor-selective antagonist NGB 2904 (1, 9H-fluorene-2-carboxylic acid {4-[(2,3-dichlorophenyl)-piperazin-1-yl]-butyl}-amide, Ki (hD3) = 2.0 nM, Ki (hD2L) = 112 nM, D2/D3 selectivity ratio of 56) was chosen as a lead structure for chemical modification in an attempt to reduce its high lipophilicity (c log D = 6.94) while optimizing D3 receptor binding affinity and D2/D3 selectivity. A series of >30 novel analogues were synthesized, and their binding affinities were evaluated in competition binding assays in HEK 293 cells transfected with either D2(L), D3, or D4 human dopamine receptors using the high affinity, selective D2-like receptor antagonist (125)I-IABN. Structural diversity in the aryl amide end of the molecule was found to have a major influence on (sub)nanomolar D3 receptor affinity and D2/D3 selectivity, which was optimized using a more rigid trans-butenyl linker between the aryl amide and the piperazine. Several analogues demonstrated superior D3 receptor binding affinities and selectivities as compared to the parent ligand. Compound 29 (N-{4-[4-(2,3-dichlorophenyl)-piperazin-1-yl]-trans-but-2-enyl}-4-pyridine-2-yl-benzamide) displayed the most promising pharmacological profile (Ki (hD3) = 0.7 nM, Ki (hD2L) = 93.3 nM, D2/D3 selectivity ratio of 133). In addition, this ligand inhibited quinpirole stimulation of mitogenesis at human dopamine D3 receptors transfected into Chinese hamster ovary (CHO) cells, with an EC50 value of 3.0 nM. Compound 29 was a nearly 5 times more potent antagonist at the D3 receptor than 1 (EC50 = 14.4 nM). Moreover, a decrease in c log D value of approximately 2 orders of magnitude was determined for this novel D3-receptor-preferring ligand, compared to 1. In summary, chemical modification of 1 has resulted in compounds with high affinity and selectivity for D3 receptors. The most promising candidate, compound 29, is currently being evaluated in animal models of cocaine abuse and will provide an important tool with which to elucidate the role of D3 receptors in drug reinforcement in vivo.

Yawning and hypothermia in rats: effects of dopamine D3 and D2 agonists and antagonists

“…While the MEDs for the inhibition of yawning by PG01037 and SB-277011A (32.0 mg/kg for both) are slightly higher than those reported for SB-277011A on a variety of operant behaviors (3.0 -24 mg/kg; Andreoli et al 2003;Di Ciano et al 2003;Xi et al 2004;Gilbert et al 2005;Xi et al 2005;Cervo et al 2007) and are likewise higher than might be expected based on in vitro D3 affinities of 0.7 nM and 10.7 nM respectively Grundt et al 2005) there is no evidence to suggest that the inhibition of yawning by these antagonists results from anything other than an antagonist activity at the D3 receptor. Not only did PG01037 and SB-277011A not inhibit sumanirole-induced hypothermia or increase yawning induced by high doses of PD-128,907 in the current studies at doses up to 56.0 mg/ kg, but SB-277011A also failed to induce catalepsy and increases plasma prolactin levels at doses up to 78.8 and 93 mg/kg; p.o.…”

“…Although several agonists and antagonists have been reported to be over 100-fold selective for either the D3 (e.g., Stemp et al 2000;Grundt et al 2005) or D2 (e.g., Vangveravong et al 2006) receptors based on in vitro binding studies, a large degree of variability exists with respect to the reported in vitro binding affinities and D2/D3 selectivity ratios. A variety of factors may account for these differences in affinity and selectivity including differences in receptor species, expression systems, radioligands, and/or assay conditions.…”

Dopamine Agonist-Induced Yawning in Rats: A Dopamine D3 Receptor-Mediated Behavior

“…Nafadotride, U99194, SB-277011A, and PG01037 have been shown to preferentially bind the D3 receptor over the D2 receptor in vitro, with D3 selectivities of approximately 3-, 30-, 100-, and 133-fold, respectively (Sautel et al, 1995;Audinot et al, 1998;Flietstra and Levant, 1998;Stemp et al, 2000;Grundt et al, 2005), and were used at behaviorally active doses (Waters et al, 1993;Vorel et al, 2002;Di Ciano et al, 2003, Leriche et al, 2003Millan et al, 2004) to examine their effects on yawning behavior in rats.…”

“…An early hypothesis regarding the biphasic regulation of apomorphine-induced yawning behavior attributed the induction of yawning behavior to a D2 agonist activity, whereas the inhibition seen at higher doses was thought to be due to a competing D1 agonist activation (Yamada and Furukawa, 1980;Urba-Holmgren et al, 1982). The cloning of the dopamine D3 receptor and the development of agonists such as PD-128,907 (Pugsley et al, 1995) and 7-OH-DPAT [(Ϯ)-7-hydroxy-2-dipropylaminotetralin HBr] (Levesque et al, 1992;Pugsley et al, 1995), as well as antagonists including U99194 (Cannon et al, 1982;Haadsma-Svensson and Svensson, 1998), SB-277011A (Reavill et al, 2000;Stemp et al, 2000), and PG01037 (Grundt et al, 2005) with greater degrees of in vitro selectivity for the D3 receptor have allowed greater insights into the regulation of dopaminergic agonist-induced yawning behavior to be made. Based on a series of studies examining the unconditioned behavioral effects of 7-OH-DPAT (Daly and Waddington, 1993;Ferrari and Giuliani, 1995;Kurashima et al, 1995), as well as binding studies (Levant et al, 1995), Levant (1997) hypothesized in an extensive review that D2/D3 agonist-induced yawning may be a D3 agonist-mediated effect, whereas the inhibition seen at higher doses was a result of concomitant D2 agonist activation.…”

Analogues of the dopamine D2 receptor antagonist L741,626: Binding, function, and SAR

“…Retention of the C-4 piperidine sp3 carbon was previously reported to be preferred by the D2 receptor 12 and replacement of the 4-piperidinol function with other groups was explored (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29). In general, none of these analogues showed higher affinity for D2 than the parent compound.…”