Solution Structures of the Prototypical 18 kDa Translocator Protein Ligand, PK 11195, Elucidated with 1H/13C NMR Spectroscopy and Quantum Chemistry
Solution Structures of the Prototypical 18 kDa Translocator Protein Ligand, PK 11195, Elucidated with 1H/13C NMR Spectroscopy and Quantum Chemistry
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DOI：
10.1021/cn3000108
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发表时间：
2012-04-01
影响因子：
5
通讯作者：
Pike, Victor W.
中科院分区：
文献类型：
--
作者：
Lee, Yong-Sok;Simeon, Fabrice G.;Pike, Victor W.
18千道尔顿转运蛋白（TSPO）是药物发现和脑和外周炎症过程的临床分子成像的重要靶点。PK 11195 [1a; 1-（2-氯苯基）-N-甲基-（1-甲基丙基）-3-异喹啉甲酰胺）是TSPO的主要原型高亲和力配体。阐明的溶液结构的la是感兴趣的理解小分子配体与亲脂性结合位点的TSPO的相互作用。动态H-1/C-13 NMR光谱的1A揭示了四个相当稳定，但相互转换的旋转异构体，由于酰胺键和2-氯苯基旋转。这些旋转异构体在先前对Ia的结构和Ia与TSPO的结合的描述中被忽略。本文采用量子化学B3 LYP/6-311+G（2d，p）方法计算了1a的旋转异构体和非常弱的TSPO配体N-去甲基-PK 11195（1b）的C-13和H-1化学位移。这些数据，加上实验NMR数据，然后被用来表征在有机溶液中的1a和1b的旋转异构体的结构。从动态H-1 NMR确定的酰胺键和2 '-氯苯基旋转1a的能量障碍是相似的（约17至18千卡/摩尔），他们比较好，在B3 LYP/6- 31 G * 水平上计算的。此外，计算出的Z到E旋转的势垒在1a中（18.7 kcal/mol）比在1b中（25.4 kcal/mol）低得多。NMR（NOE）明确地证明1a的E旋转异构体在溶液中更稳定，约0.4 kcal/mol。这些详细的结构研究结果将有助于未来的TSPO配体的设计和支持的概念，TSPO更喜欢结合作为酰胺E-旋转异构体的配体。
Eighteen kilodalton translocator protein (TSPO) is an important target for drug discovery and for clinical molecular imaging of brain and peripheral inflammatory processes. PK 11195 [1a; 1-(2-chlorophenyl)-N-methyl-(1-methylpropyl)-3-isoquinoline carboxamide) is the major prototypical high-affinity ligand for TSPO. Elucidation of the solution structure of la is of interest for understanding small-molecule ligand interactions with the lipophilic binding site of TSPO. Dynamic H-1/C-13 NMR spectroscopy of 1a revealed four quite stable but interconverting rotamers, due to amide bond and 2-chlorophenyl group rotation. These rotamers have been neglected in previous descriptions of the structure of la and of the binding of 1a to TSPO. Here, we used quantum chemistry at the level of B3LYP/6-311+G(2d,p) to calculate C-13 and H-1 chemical shifts for the rotamers of 1a and for the very weak TSPO ligand, N-desmethyl-PK 11195 (1b). These data, plus experimental NMR data, were then used to characterize the structures of rotamers of 1a and 1b in organic solution. Energy barriers for both the amide bond and 2'-chlorophenyl group rotation of 1a were determined from dynamic H-1 NMR to be similar (ca.17 to 18 kcal/mol), and they compared well with those calculated at the level of B3LYP/6-31G*. Furthermore, the computed barrier for Z to E rotation is considerably lower in 1a (18.7 kcal/mol) than in 1b (25.4 kcal/mol). NMR (NOE) unequivocally demonstrated that the E rotamer of 1a is the more stable in solution by about 0.4 kcal/mol. These detailed structural findings will aid future TSPO ligand design and support the notion that TSPO prefers to bind ligands as amide E-rotamers.