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首页> 外文期刊>Chemistry: A European journal >A computational study of regioselectivity in a cyclodextrin-mediated diels-alder reaction: revelation of site selectivity and the importance of shallow binding and multiple binding modes
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A computational study of regioselectivity in a cyclodextrin-mediated diels-alder reaction: revelation of site selectivity and the importance of shallow binding and multiple binding modes

机译：环糊精介导的狄尔斯-阿尔德反应中区域选择性的计算研究：揭示位点选择性以及浅结合和多重结合方式的重要性

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The use of a cyclodextrin·Diels-Alder transition structure complex (CD·TS) as a model in molecular dynamic simulations has enabled us to gain insight into the controlling factors in the cyclodextrin-mediated Diels-Alder reaction of methyl-p-benzoquinone with isoprene. MD simulations were carried out with multiple binding configurations of the CD·TS (TS = meta-TS, para-TS) complexes at the top and bottom rims of beta-CD. We discovered that i) only shallow binding with the CD is necessary for the regioselectivity, and multiple binding geometries are possible; ii) the narrow bottom rim, with the primary hydroxyl groups, of the CD binds both regio-TSs better than at the wider top rim (secondary hydroxyl groups), which was unexpected from the perspective of shape complementarity that governs the stability of most CD·guest complexes. Overall, the bottom rim of the CD exhibits higher regioisomer discrimination for the meta-TS; iii) structural clustering analyses of the CD·TS configurations (sampled during MD simulations) have enabled us to evaluate the binding energies of the different binding configurations. The result indicates that there is a direct correlation between meta-product selectivity and a higher number of binding configurations favoring the formation of the CD·meta-TS complex. The main forces of stabilization in the CD·TS complexes are the van der Waals interactions when the TS is bound at the top rim. At the bottom rim, closer contacts between polar functional groups of the TS and CD have increased the importance of electrostatic interactions. We found that van der Waals, solvation, and torsional forces are less favorable for complexation at the bottom rim; however, this is compensated by large favorable electrostatic interactions. With insights obtained from the study of CD·TS complexes and MD simulations of the modified heptakis-[6-O-(2-hydroxy)propyl]-beta-CD, we were able to explain why a low selectivity was observed when the Diels-Alder reaction was carried out in this modified CD. Two types of search method [Monte Carlo and multiple minimum (MCMM) and molecular dynamics (MD)] to explore and evaluate the different possible binding geometries of the TS within beta-CD, were discussed.
机译：在分子动力学模拟中使用环糊精·Diels-Alder过渡结构配合物（CD·TS）作为模型，使我们能够深入了解环糊精介导的甲基对苯醌与Diels-Alder反应的控制因素。异戊二烯。 MD模拟是在β-CD顶部和底部边缘的CD·TS复合物（TS = meta-TS，对TS）复合物的多种结合构型下进行的。我们发现：i）对于区域选择性，仅需与CD进行浅层结合即可，并且可能有多种结合几何形状; ii）CD的窄底边带有伯羟基，与两个regio-TS的结合要好于较宽的顶边（仲羟基），从形状互补性的角度来看，这是决定大多数CD稳定性的原因，这是出乎意料的·客运大楼。总体而言，CD的底部边缘对meta-TS表现出更高的区域异构体区分; iii）CD·TS构型的结构聚类分析（在MD模拟过程中采样）使我们能够评估不同结合构型的结合能。结果表明，在元产物的选择性和较高数量的结合构型之间存在直接的相关性，这有利于CD·meta-TS复合物的形成。当TS结合在顶部边缘时，CD·TS复合物中稳定的主要力量是范德华相互作用。在底部边缘，TS和CD的极性官能团之间更紧密的接触增加了静电相互作用的重要性。我们发现范德华力，溶剂化作用力和扭转力不利于底部边缘的复杂化。但是，这可以通过大量有利的静电相互作用来补偿。通过对CD·TS配合物的研究和改性庚七-[6-O-（2-羟基）丙基]β-CD的MD模拟获得的见解，我们能够解释为什么当Diels时观察到低选择性-在该改性的CD中进行der醛反应。讨论了两种搜索方法[Monte Carlo和多重最小（MCMM）和分子动力学（MD）]，以探索和评估β-CD中TS的不同可能的结合几何形状。

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