Synthesis of quinoxaline cavitand baskets

ABSTRACT

The unique temperature, solvent and pH drivenvase to kite equilibrium in quinoxaline cavitands allows the reversible uptake and release of guests. However, the cavity breathing associated with this conformational switch reduces the strength of complexation. A limited number of solutions have been proposed for the cavity rigidification, using either H-bonding, metal coordination or covalent connections. Here we report the synthesis and structural characterisation of quinoxaline-based cavitand baskets, which present two distal quinoxaline walls linked together. Baskets A and B were obtained through a bridging reaction starting from an AC di-quinoxaline bridged cavitand using two different di-quinoxaline moieties. In both cases, two isomers were obtained: isomer C₂, with the linking unit crossing the cavity mouth, and isomer C_s, having the linker sideways. The isomers were identified through ¹H NMR analysis. In the case of basket A-C_s, the resolved molecular structure confirmed the C_s symmetry of the basket.

Grapical abstract

KEYWORDS:

• Quinoxaline cavitands
• cavity partial rigidification
• X-ray crystal structure
• upper rim bridging

Acknowledgments

This work has benefitted from the equipment and framework of the COMP-HUB Initiative, funded by the ‘Departments of Excellence’ program of the Italian Ministry for Education, University and Research (MIUR, 2018-2022). The authors acknowledge MIUR through the PRIN project 20179BJNA2 for financial support. The authors acknowledge the Centro Interdipartimentale di Misure “G. Casnati” of the University of Parma for the use of NMR facilities and Prof. D. Bonifazi of the University of Vienna for MALDI-TOF analyses. Chiesi Farmaceutici SpA is acknowledged for its support with the D8Venture X-ray equipment.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Ministero dell’Istruzione, dell’Università e della Ricerca [PRIN project 20179BJNA2].