Cyclosporins of symmetry P2(1) - a series of clathrates

A series of isomorphous clathrates (cyclosporin A: solvent = 1 : 1) is repo rted. The structure of the tetrahydrofuran ( 1) and dibutylether (2) clathr ates have been determined by X-ray single crystal diffraction. The cyclospo rin molecules in both structures are associated via van der Waals interacti ons forming cavities occupied by solvent molecules. The structure refinemen t based on room-temperature data sets show significant disorder of the side chains of the cyclosporin A molecule with no adequate model of the solvent molecule in both structures. In contrast, the position of dibutylether was successfully localised using a low-temperature data set for 2.