Unprecedented chiral molecular recognition in a C3-symmetric environment
Unprecedented chiral molecular recognition in a C3-symmetric environment
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DOI：
10.1021/ja0119696
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发表时间：
2002-01-30
影响因子：
15
通讯作者：
Ahn, KH
中科院分区：
文献类型：
--
作者：
Kim, SG;Kim, KH;Ahn, KH
研究了苯基三脚架三恶唑啉受体对α-手性伯铵离子的对映体识别。与文献和我们的预期相反，观察到一个良好的水平的手性歧视的三脚架受体，这提供了一个C-3对称的手性环境的客人结合。手性歧视已被发现是一般的情况下，α-芳基取代的客人，这表明π-π相互作用的一个重要因素。这一结果引起了关于手性区别的起源的问题，因为预期在非对映体包合络合物之间几乎没有空间或电子差异，通过NMR滴定和等温滴定量热法研究了手性对映体的结合作用，结果表明，非对映体间的热力学稳定性不同是手性识别的原因，客体络合物的形成是由有利的焓变化驱动的，而熵变化具有较小的负贡献。两个非对映体包合物的X-射线晶体结构的解析，明确显示的结合模式，并提供线索的手性歧视的起源。键角分析表明，小的复杂的经验更大的空间应变，这是可辨别的，当它被视为从“三体”之间的相互作用的主机和客户。客体和恶唑啉苯环堆叠良好，表明π-π相互作用的相互作用。π-π相互作用被认为是稳定的主体-客体复合物，从而赋予高度灵活的受体以实质性的对映体歧视。
The enantiomeric recognition of alpha-chiral primary ammonium ions has been studied with benzene-based tripodal tris(oxazoline) receptors. Contrary to the literature and our expectation, a good level of chiral discrimination is observed with one of the tripodal receptors, which provides a C-3-symmetric chiral environment on guest binding. The chiral discrimination has been found to be general in the case of alpha-aryl substituted guests, suggesting pi-pi interactions as an important factor. This result raises a question with respect to the origin of the chiral discrimination since little steric or electronic difference is expected between the diastereomeric inclusion complexes, Binding studies by NMR titration and isothermal titration calorimetry show that the chiral discrimination results from the different thermodynamic stabilities between the diastereomeric complexes and that the host-guest complex formation is driven by favorable enthalpy changes with a minor negative contribution by entropy changes. The X-ray crystal structures for both of the diastereomeric inclusion complexes are resolved, which unambiguously show the binding mode and provide clues on the origin of the chiral discrimination. Bond angle analyses indicate that the minor complex experiences a larger steric strain, which is discernible when it is viewed from "three-body" interactions between the host and the guest. The guest and oxazoline phenyl rings are well stacked, indicating interplay of the pi-pi interactions. The pi-pi interactions are believed to stabilize host-guest complexes, thereby endowing the highly flexible receptors with a substantial enantio-discrimination.