Department of Advanced Materials Chemistry, Graduate School of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan.
Org Biomol Chem. 2018 Jan 3;16(2):213-222. doi: 10.1039/c7ob02318a.
Chiral anionic species are ubiquitous and play important roles in biological systems. Despite the recent advancements in synthetic anion receptors bearing urea functionalities, urea-based chiral solvating agents (CSAs) that can separate the NMR signals of racemic anions remain limited. Herein, three dibenzofuran-based C-symmetric chiral bisureas were synthesized from the reaction of (R,R)-4,6-bis(1-aminopropyl)dibenzo[b,d]furan with phenyl isocyanate, phenyl thioisocyanate, or tosyl isocyanate. The chiral anion recognition properties of these bisureas were examined by H NMR spectroscopy using dl-tetrabutylammonium mandelate (TBAM) as a model substrate. A clear baseline separation of the enantiomeric signals of the benzylic proton of TBAM was achieved upon mixing with 0.5 equivalents of bis(phenylurea). In contrast to previous urea-based chiral anion receptors that differentiate the enantiomers of chiral anions by forming 1 : 1 host-guest complexes, a high chiral recognition ability of chiral bis(phenylurea) was achieved owing to the generation of an equilibrium between free guests, 1 : 1 host-guest complexes, and 1 : 2 host-guest complexes. Chiral bis(phenylurea) was also successfully employed in the separation of the enantiomeric H NMR signals of various racemic anions.
手性阴离子物种普遍存在，并在生物系统中发挥重要作用。尽管最近在带有脲官能团的合成阴离子受体方面取得了进展，但能够分离外消旋阴离子 NMR 信号的基于脲的手性溶剂化试剂（CSA）仍然有限。本文中，通过（R,R）-4,6-双（1-氨基丙基）二苯并[b,d]呋喃与苯基异氰酸酯、苯基硫代异氰酸酯或对甲苯磺酰异氰酸酯的反应，合成了三种基于二苯并呋喃的 C 对称手性双脲。通过使用 dl-四丁基铵扁桃酸盐（TBAM）作为模型底物的 H NMR 光谱研究了这些双脲的阴离子识别特性。与 0.5 当量的双（苯基脲）混合后，TBAM 的苄基质子的对映异构体信号实现了明显的基线分离。与通过形成 1：1 主客体配合物来区分手性阴离子对映异构体的基于脲的先前手性阴离子受体不同，由于在游离客体、1：1 主客体配合物和 1：2 主客体配合物之间产生平衡，手性双（苯基脲）表现出高的手性识别能力。手性双（苯基脲）还成功地用于分离各种外消旋阴离子的对映体 H NMR 信号。
