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首页> 外文期刊>Chemistry: A European journal >Unraveling the role of water in the stereoselective step of aqueous proline-catalyzed aldol reactions
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Unraveling the role of water in the stereoselective step of aqueous proline-catalyzed aldol reactions

机译：阐明水在脯氨酸水溶液催化的醛醇缩合反应立体选择步骤中的作用

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A multiscale computational study was performed with the aim of tracing the source of stereoselectivity and disclosing the role of water in the stereoselective step of propionaldehyde aldol self-condensation catalyzed by proline amide in water, a reaction that serves as a model for aqueous organocatalytic aldol condensations. Solvent mixing and hydration behavior were assessed by classical molecular dynamics simulations, which show that the reaction between propanal and the corresponding enamine takes place in a fully hydrated environment. First-principles molecular dynamics simulations were used to study the free-energy profile of four possible reaction paths, each of which yields a different stereoisomer, and high-level static first-principles calculations were employed to characterize the transition states for microsolvated species. The first solvation shell of the oxygen atom of the electrophilic aldehyde at the transition states contains two water molecules, each of which donates one hydrogen bond to the nascent alkoxide and thereby largely stabilizes its excess electron density. The stereoselectivity originates in an extra hydrogen bond donated by the amido group of proline amide in two reaction paths. Different solvation patterns of the possible transition states have been traced as the source of the stereoselectivity of a key organocatalytic reaction-the proline-catalyzed asymmetric aldol condensation of propionaldehyde in water-by means of extensive first-principles molecular dynamics (MD) simulations. For example, the figure shows MD snapshots for Si-Si (red line) and Re-Re attack (blue line).
机译：进行了多尺度计算研究，其目的是追踪立体选择性的来源，并揭示水在水中脯氨酸酰胺催化的丙醛羟醛自缩合的立体选择步骤中的作用，该反应可作为水性有机催化羟醛缩合的模型。通过经典的分子动力学模拟评估了溶剂的混合和水合行为，结果表明丙醛与相应的烯胺之间的反应发生在完全水合的环境中。第一性原理分子动力学模拟用于研究四种可能的反应路径的自由能谱，每种反应路径产生不同的立体异构体，并采用高级静态第一性原理计算来表征微溶剂化物种的过渡态。处于过渡态的亲电子醛的氧原子的第一个溶剂化壳包含两个水分子，每个水分子均向新生的醇盐提供一个氢键，从而大大稳定了其多余的电子密度。立体选择性起源于脯氨酸酰胺的酰胺基在两个反应路径中提供的额外氢键。借助广泛的第一性原理分子动力学（MD）模拟，已经追踪了可能的过渡态的不同溶剂化模式，作为关键有机催化反应（脯氨酸催化丙醛在水中的不对称醛醇缩合醛醇缩合）的立体选择性的来源。例如，该图显示了Si-Si（红线）和Re-Re攻击（蓝线）的MD快照。

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