Differing Activity Profiles of the Stereoisomers of 2,3,5,6TMP-TQS, a Putative Silent Allosteric Modulator of <i>α</i>7 nAChR
作者:Roger L. Papke、Sumanta Garai、Clare Stokes、Nicole A. Horenstein、Arthur D. Zimmerman、Khalil A. Abboud、Ganesh A. Thakur
DOI:10.1124/mol.120.119958
日期:2020.10
Many synthetic compounds to which we attribute specific activities are produced as racemic mixtures of stereoisomers, and it may be that all the desired activity comes from a single enantiomer. We have previously shown this to be the case with the α 7 nicotinic acetylcholine receptor positive allosteric modulator (PAM) 3a,4,5,9b-Tetrahydro-4-(1-naphthalenyl)-3H-cyclopentan[c]quinoline-8-sulfonamide (TQS) and the α 7 ago-PAM 4BP-TQS. Cis-trans-4-(2,3,5,6-tetramethylphenyl)-3a,4,5,9b-te-trahydro-3H-cyclopenta[c]quinoline-8-sulfonamide (2,3,5,6TMP-TQS), previously published as a “silent allosteric modulator” and an antagonist of α 7 allosteric activation, shares the same scaffold with three chiral centers as the aforementioned compounds. We isolated the enantiomers of 2,3,5,6TMP-TQS and determined that the (−) isomer was a significantly better antagonist than the (+) isomer of the allosteric activation of both wild-type α 7 and the nonorthosterically activatible C190A α 7 mutant by the ago-PAM GAT107 (the active isomer of 4BP-TQS). In contrast, (+)2,3,5,6TMP-TQS proved to be an α 7 PAM. (−)2,3,5,6TMP-TQS was shown to antagonize the allosteric activation of α 7 by the structurally unrelated ago-PAM B-973B as well as the allosteric activation of the TQS-sensitive α 4 β 2L15′M mutant. In silico docking of 2,3,5,6TMP-TQS in the putative allosteric activation binding site suggested a specific interaction of the (−) enantiomer with α 7T106, and allosteric activation of α 7T106 mutants was not inhibited by (−)2,3,5,6TMP-TQS, confirming the importance of this interaction and supporting the model of the allosteric binding site. Comparisons and contrasts between 2,3,5,6TMP-TQS isomers and active and inactive enantiomers of other TQS-related compounds identify the orientation of the cyclopentenyl ring to the plane of the core quinoline to be a crucial determinate of PAM activity. SIGNIFICANCE STATEMENT Many synthetic ligands are in use as racemic preparations. We show that one enantiomer of the TQS analog Cis-trans-4-(2,3,5,6-tetramethylphenyl)-3a,4,5,9b-te-trahydro-3H-cyclopenta[c]quinoline-8-sulfonamide, originally reported to lack activity when used as a racemic preparation, is an α 7 nicotinic acetylcholine receptor positive allosteric modulator (PAM). The other enantiomer is not a PAM, but it is an effective allosteric antagonist. In silico studies and structural comparisons identify essential elements of both the allosteric ligands and receptor binding sites important for these allosteric activities.
许多我们认定具有特定活性的合成化合物是以外消旋混合物的形式产生,这些混合物由立体异构体组成,可能所有所需的活性都来自单一的对映异构体。我们之前已经证明,对于α7烟碱型乙酰胆碱受体正变构调节剂(PAM)3a,4,5,9b-四氢-4-(1-萘基)-3H-环戊[c]喹啉-8-磺酰胺(TQS)和α7 ago-PAM 4BP-TQS,情况确实如此。顺反-4-(2,3,5,6-四甲基苯基)-3a,4,5,9b-四氢-3H-环戊[c]喹啉-8-磺酰胺(2,3,5,6TMP-TQS),先前被发表为一种“沉默的变构调节剂”和α7变构激活的拮抗剂,与上述化合物共享相同的骨架和三个手性中心。我们分离了2,3,5,6TMP-TQS的对映体,并确定(-)异构体在拮抗野生型α7和非正构激活的C190A α7突变体由ago-PAM GAT107(4BP-TQS的活性异构体)引起的变构激活方面,显著优于(+)异构体。相比之下,(+)2,3,5,6TMP-TQS被证明是一种α7 PAM。(-)2,3,5,6TMP-TQS也被显示能拮抗由结构不相关的ago-PAM B-973B引起的α7的变构激活,以及TQS敏感的α4β2 L15'M突变体的变构激活。在计算机模拟对接中,2,3,5,6TMP-TQS在假想的变构激活结合位点显示出(-)对映体与α7T106的特定相互作用,而α7T106突变体的变构激活并未被(-)2,3,5,6TMP-TQS抑制,这证实了这种相互作用的重要性,并支持了变构结合位点的模型。在2,3,5,6TMP-TQS异构体与活性及非活性对映体的其他TQS相关化合物之间的比较和对比中,环戊烯环相对于核心喹啉平面的取向被确定为PAM活性的关键决定因素。
**意义声明**
许多合成配体被用作外消旋制剂。我们展示了一种TQS类似物顺反-4-(2,3,5,6-四甲基苯基)-3a,4,5,9b-四氢-3H-环戊[c]喹啉-8-磺酰胺的对映体,原先报告称当作为外消旋制剂使用时缺乏活性,实际上是一种α7烟碱型乙酰胆碱受体正变构调节剂(PAM)。另一种对映体不是PAM,但它是一种有效的变构拮抗剂。计算机模拟研究和结构比较确定了对于这些变构活性重要的变构配体和受体结合位点的关键要素。