Zhu Lei, Shabbir Shagufta H, Gray Mark, Lynch Vincent M, Sorey Steven, Anslyn Eric V
Department of Chemistry and Biochemistry, The University of Texas at Austin, 78712, USA.
J Am Chem Soc. 2006 Feb 1;128(4):1222-32. doi: 10.1021/ja055817c.
o-(Pyrrolidinylmethyl)phenylboronic acid (4) and its complexes with bifunctional substrates such as catechol, alpha-hydroxyisobutyric acid, and hydrobenzoin have been studied in detail by X-ray crystallography, (11)B NMR, and computational analysis. The N-B interactions in analogous boronic acids and esters have been extensively cited in molecular recognition and chemosensing literature. The focal point of this study was to determine the factors that are pertinent to the formation of an intramolecular N-B dative bond. Our structural study predicts that the formation of an N-B dative bond, and/or solvent insertion to afford a tetrahedral boronate anion, depends on the solvent and the complexing substrate present. Specifically, from (11)B NMR studies, complexation of 4 with electron-withdrawing and/or vicinally bifunctionalized substrates promotes both the formation of N-B dative bonds and the solvation of sp(2) boron to a tetrahedral sp(3) boronate. In the solid state, the presence of an N-B dative bond in the complex of 4 and catechol (7) depends on the solvent from which it crystallizes. From chloroform, an N-B bond was observed, whereas from methanol, a methoxylated boronate was formed, where the methoxy group is hydrogen-bonded with the neighboring tertiary ammonium ion. The structural optimization of compounds 4 and 7 using density functional theory in a simulated water continuum also predicts that complexation of 4 and catechol promotes either the formation of an N-B bond or solvolysis if 1 equiv of water is present. The conclusion from this study will help in the design of future chemosensing technologies based on o-(N,N-dialkylaminomethyl)arylboronate scaffolds that are targeting physiologically important substances such as saccharides, alpha-hydroxycarboxylates, and catecholamines.
已通过X射线晶体学、¹¹B核磁共振和计算分析对邻（吡咯烷基甲基）苯硼酸（4）及其与双功能底物（如儿茶酚、α-羟基异丁酸和氢化苯偶姻）形成的配合物进行了详细研究。类似硼酸和硼酸酯中的N-B相互作用在分子识别和化学传感文献中已有广泛引用。本研究的重点是确定与分子内N-B配位键形成相关的因素。我们的结构研究预测，N-B配位键的形成和/或溶剂插入以提供四面体硼酸根阴离子，取决于存在的溶剂和络合底物。具体而言，通过¹¹B核磁共振研究，4与吸电子和/或邻位双官能化底物的络合促进了N-B配位键的形成以及sp²硼向四面体sp³硼酸根的溶剂化。在固态下，4与儿茶酚（7）的配合物中N-B配位键的存在取决于其结晶所用的溶剂。从氯仿中结晶时，观察到N-B键，而从甲醇中结晶时，则形成了甲氧基化的硼酸酯，其中甲氧基与相邻的叔铵离子形成氢键。在模拟水连续介质中使用密度泛函理论对化合物4和7进行结构优化也预测，如果存在1当量的水，4与儿茶酚的络合会促进N-B键的形成或溶剂解。本研究的结论将有助于基于邻（N,N-二烷基氨基甲基）芳基硼酸酯支架设计未来的化学传感技术，这些支架可靶向糖类、α-羟基羧酸盐和儿茶酚胺等生理上重要的物质。
