Strychnine is the prototypic antagonist of glycine receptors, a family of pentameric ligand-gated ion channels. Recent high-resolution structures of homomeric glycine receptors have confirmed the presence of five orthosteric binding sites located in the extracellular subunit interfaces of the receptor complex that are targeted by strychnine. Here, we report the synthesis and extensive pharmacological evaluation of bivalent ligands composed of two strychnine pharmacophores connected by appropriate spacers optimized toward simultaneous binding to two adjacent orthosteric sites of homomeric α1 glycine receptors. In all bivalent ligands, the two strychnine units were linked through C-2 by amide spacers of various lengths ranging from 6 to 69 atoms. Characterization of the compounds in two functional assays and in a radioligand binding assay indicated that compound 11a, with a spacer consisting of 57 atoms, may be capable of bridging the homomeric α1 GlyRs by simultaneous occupation of two adjacent strychnine-binding sites. The findings are supported by docking experiments to the crystal structure of the homomeric glycine receptor. Based on its unique binding mode, its relatively high binding affinity and antagonist potency, and its slow binding kinetics, the bivalent strychnine analogue 11a could be a valuable tool to study the functional properties of glycine receptors.

中文翻译：

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C-2-连接的二聚马钱子碱类似物作为靶向甘氨酸受体的二价配体

马钱子碱是甘氨酸受体的原型拮抗剂，甘氨酸受体是五聚体配体门控离子通道家族。最近的同源甘氨酸受体的高分辨率结构已经证实存在五个正构结合位点，位于受体复合物的细胞外亚基界面，这些位点是士的宁靶向的。在这里，我们报告了由两个士的宁药效团组成的二价配体的合成和广泛的药理学评估，这些配体通过适当的间隔物连接，优化为同时结合同聚 α1 甘氨酸受体的两个相邻正构位点。在所有二价配体中，两个士的宁单元通过 C-2 由不同长度的 6 到 69 个原子的酰胺间隔键连接。具有由57个原子组成的间隔基的图11a可能能够通过同时占据两个相邻的士的宁结合位点来桥接同聚α1 GlyR。这些发现得到了同聚甘氨酸受体晶体结构对接实验的支持。基于其独特的结合模式、相对较高的结合亲和力和拮抗剂效力以及缓慢的结合动力学，二价士的宁类似物11a可能是研究甘氨酸受体功能特性的宝贵工具。