Abstract
A new class of bambus[4]urils (BU[4]s) composed of asymmetric N,N′-disubstituted glycoluril subunits with different alkyl groups were designed, synthesized, and fully characterized by NMR techniques and X-ray crystallography. Structural studies showed that four macrocyclic diastereoisomers are possible: two Sn symmetric achiral macrocycles and two macrocycles that are "inherently"chiral. The relative "head-to-tail"arrangement of the N-substituents in Bn4Me4BU[4], 5a, clearly observed by X-ray spectroscopy analysis, determines the overall symmetry of the bambusuril structure. Chiral Pr4Me4BU[4], 4b, was resolved by chiral high-performance liquid chromatography (HPLC) into its enantiomers, and all four inherently chiral bambusuril pairs (two Pr4Me4BU[4] and two Bn4Me4BU[4] stereoisomers, 4b, 4d, 5b, and 5d) were clearly observed by 1H NMR spectroscopy with the aid of (R)-BINOL as a chiral solvating agent. This latter methodology provides a rapid and powerful approach for investigating the enantiopurity of inherently chiral cavitands, which complements and augments the conventional chromatographic approaches.
| Original language | English |
|---|---|
| Pages (from-to) | 9190-9200 |
| Number of pages | 11 |
| Journal | Journal of Organic Chemistry |
| Volume | 85 |
| Issue number | 14 |
| DOIs | |
| State | Published - 17 Jul 2020 |
Bibliographical note
Funding Information:Financial support for this work was provided by the Ministry of Science Technology and Space (MOST grant no. 3-10855). We thank Dr. Natalia Fridman from the crystallographic lab at the Schulich Faculty of Chemistry, Technion, for her valuable contribution to the X-ray crystallographic efforts. We thank Prof. Doron Pappo from the Department of Chemistry, Ben-Gurion University of the Negev, for providing optically pure ( R)-BINOL II – V derivatives for this study. We also thank Prof. N. Gabriel Lemcoff for his valuable comments on this manuscript.
Publisher Copyright:
Copyright © 2020 American Chemical Society.