Novel 2-substituted-5-(4-chloro-2-phenoxy)phenyl-1,3,4-oxadiazole derivatives, ligands of GABAa/benzodiazepine receptor complex: design, synthesis, radioligand binding assay, and pharmacological evaluation

Agonists of Benzodiazepine (BZD) receptor are exhaustively used in the control of muscle spasms, seizure, anxiety, and insomnia. BZDs have some unwanted effects; therefore, the development of new BZD receptor agonists with better efficacy and fewer unwanted effects is one of the subjects of interest. In this study, based on the pharmacophore/receptor model of the BZD binding site of GABAA receptors, a series of new 2-substituted-5-(4-chloro-2-phenoxy)phenyl-1,3,4-oxadiazole derivatives (6a-f) were designed. Energy minima conformers of the designed compounds and diazepam were well matched in conformational analysis and showed proper interaction with the BZD-binding site of the GABAA receptor model (α1β2ϒ2) in docking studies. The designed compounds were synthesized in acceptable yield and evaluated for their in vitro affinity to the benzodiazepine receptor of rat brains by radioligand receptor binding assay. The results demonstrated that the affinities of most of the novel compounds were even higher than diazepam. The novel compound 6a with the best affinity in radioligand receptor binding assay (Ki=0.44 nM and IC50= 0.73±0.17 nM) had considerable hypnotic activity and weak anticonvulsant and anxiolytic effects with no negative effect on memory in animal models. Flumazenil as a selective benzodiazepine receptor antagonist was able to prevent hypnotic and anticonvulsant effects of 6a indicating the role of BZD receptors in these effects.

苯二氮䓬（Benzodiazepine, BZD）受体激动剂被广泛应用于肌肉痉挛、癫痫、焦虑及失眠的临床治疗。苯二氮䓬类药物（BZDs）存在诸多不良反应，因此开发疗效更优、不良反应更少的新型BZD受体激动剂是当前的研究热点之一。本研究基于GABAA受体BZD结合位点的药效团/受体模型，设计了一系列新型2-取代-5-(4-氯-2-苯氧基)苯基-1,3,4-噁二唑衍生物（6a-f）。构象分析结果显示，所设计化合物与地西泮（diazepam）的能量最低构象匹配度良好；分子对接研究表明，此类化合物可与GABAA受体模型（α1β2γ2）的BZD结合位点形成合理的相互作用。所设计化合物以可接受的收率完成合成，并通过放射性配体受体结合实验，评价了其对大鼠脑内苯二氮䓬受体的体外亲和力。实验结果表明，多数新型化合物的亲和力甚至高于地西泮。其中，在放射性配体受体结合实验中展现最优亲和力的新型化合物6a（Ki=0.44 nM，IC50=0.73±0.17 nM）在动物模型中具有显著的催眠活性，同时表现出较弱的抗惊厥与抗焦虑作用，且未对记忆产生负面影响。选择性苯二氮䓬受体拮抗剂氟马西尼（Flumazenil）能够阻断6a的催眠与抗惊厥效应，这证实了BZD受体在该类生物学效应中的核心作用。