Synthesis and Recognition Properties of Cucurbit[8]uril Derivatives.

A building block approach to the synthesis of Me4CB[8] and Cy2CB[8] by condensation of glycoluril hexamer 1 with bis(cyclic ethers) 2 is reported. X-ray crystallography demonstrates that the equatorial substitution results in an ellipsoidal cavity. Me4CB[8] and Cy2CB[8] display enhanced aqueous solubility and retain the ability to bind to guests (3-9) typical of unsubstituted CB[8]. The higher inherent solubility of Me4CB[8] allowed it to be used as a solubilizing excipient for insoluble drugs.