Wellendorph Petrine, Høg Signe, Greenwood Jeremy R, de Lichtenberg Anne, Nielsen Birgitte, Frølund Bente, Brehm Lotte, Clausen Rasmus P, Bräuner-Osborne Hans
Department of Medicinal Chemistry, The Danish University of Pharmaceutical Sciences, Copenhagen, Denmark.
J Pharmacol Exp Ther. 2005 Oct;315(1):346-51. doi: 10.1124/jpet.105.090472. Epub 2005 Jul 12.
Gamma-hydroxybutyrate (GHB) is a psychotropic compound endogenous to the brain. Despite its potentially great physiological significance, its exact molecular mechanism of action is unknown. GHB is a weak agonist at GABA(B) receptors, but there is also evidence of specific GHB receptor sites, the molecular cloning of which remains a challenge. Ligands with high affinity and specificity for the reported GHB binding site are needed for pharmacological dissection of the GHB and GABA(B) effects and for mapping the structural requirements of the GHB receptor-ligand interactions. For this purpose, we have synthesized and assayed three conformationally restricted GHB analogs for binding against the GHB-specific ligand [3H]NCS-382 [(E,RS)-(6,7,8,9-tetrahydro-5-hydroxy-5H-benzocyclohept-6-ylidene-)acetic acid] in rat brain homogenate. The cyclohexene and cyclopentene analogs, 3-hydroxycyclohex-1-enecarboxylic acid [(RS)-HOCHCA] and 3-hydroxycyclopent-1-enecarboxylic acid [(RS)-HOCPCA], were found to be high-affinity GHB ligands, with IC50 values in the nanomolar range, and had 9 and 27 times, respectively, higher affinity than GHB. The stereo-selectively synthesized R,R-isomer of the trans-cyclopropyl GHB analog, HOCPrCA, proved to have 10-fold higher affinity than its enantiomer. Likewise, the R-enantiomers of HOCHCA and HOCPCA selectively inhibited [3H]NCS-382 binding. The best inhibitor of these, (R)-HOCPCA, has an affinity 39 times higher than GHB and is thus among the best GHB ligands reported to date. Neither of the cycloalkenes showed any affinity (IC50 > 1 mM) for GABA(A) or GABA(B) receptors. These compounds show excellent potential as lead structures and novel tools for studying specific GHB receptor-mediated pharmacology.
γ-羟基丁酸（GHB）是大脑内源性的精神活性化合物。尽管其具有潜在的重大生理意义，但其确切的分子作用机制尚不清楚。GHB是GABA(B)受体的弱激动剂，但也有证据表明存在特定的GHB受体位点，其分子克隆仍然是一个挑战。为了对GHB和GABA(B)效应进行药理学剖析以及确定GHB受体-配体相互作用的结构要求，需要对已报道的GHB结合位点具有高亲和力和特异性的配体。为此，我们合成并测定了三种构象受限的GHB类似物，用于在大鼠脑匀浆中与GHB特异性配体[3H]NCS-382[（E，RS）-（6,7,8,9-四氢-5-羟基-5H-苯并环庚-6-亚基）乙酸]结合。环己烯和环戊烯类似物，3-羟基环己-1-烯羧酸[（RS）-HOCHCA]和3-羟基环戊-1-烯羧酸[（RS）-HOCPCA]，被发现是高亲和力的GHB配体，IC50值在纳摩尔范围内，其亲和力分别比GHB高9倍和27倍。反式环丙基GHB类似物HOCPrCA的立体选择性合成的R，R-异构体的亲和力比其对映体高10倍。同样，HOCHCA和HOCPCA的R-对映体选择性抑制[3H]NCS-382结合。其中最佳抑制剂（R）-HOCPCA的亲和力比GHB高39倍，因此是迄今为止报道的最佳GHB配体之一。这两种环烯烃对GABA(A)或GABA(B)受体均无任何亲和力（IC50>1 mM）。这些化合物作为研究特定GHB受体介导的药理学的先导结构和新型工具具有极好的潜力。
