A new class of bambusurils (BUs) 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, 5a, clearly observed by X-ray spectroscopy analysis, determines the overall symmetry of the bambusuril structure. Chiral Pr4Me4BU, 4b, was resolved by chiral high-performance liquid chromatography (HPLC) into its enantiomers, and all four inherently chiral bambusuril pairs (two Pr4Me4BU and two Bn4Me4BU 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.
ASJC Scopus subject areas
- Organic Chemistry