Combination of calix[4]arenes and resorcin[4]arenes for the complexation of steroids

Receptor molecules with large cavities synthesized by the combination of building blocks that already possess a cavity, viz. calix[4]arenes and resorcin[4]arenes, are described. These receptor molecules are synthesized by reaction of one or two upper rim 1,2-difunctionalized calix[4]arene fragments oriented either endo or exo toward a cavitand unit. The endo:exo ratio depends on the substituents at the 3- and 4-positions of the calix[4]arenes. These novel receptor molecules complex steroids with association constants of (0.9−9.5) × 10² M^-1 in CDCl₃.