Synthetic receptors: a modular approach to large structures

Combination of medium-sized building blocks comprises a new strategy for the synthesis of artificial receptor molecules. These building blocks should have relatively rigid structures to which functional groups can be attached, such as calix[4]- and -[6]arenes, resorcin[4]arenes, porphyrins, and cyclodextrins. Combination of a (3- cyclodextrin with a calix[4]arene moiety resulted in water soluble receptor molecules. Large multifunctional receptors have been prepared by the covalent combination of two calix[4]arenes and one Zn-tetraarylporphyrin. The controlled conformation of p-tert-butylcalix[6]arenes which are alternately substituted with methoxy groups, was used to synthesize a cryptocalix[6]arene consisting of a calix[6]arene and a cyclotriveratrylene unit. A new type of diastereoisomerism (carceroisomerism) was found during the synthesis of carceplexes constructed from one calix[4]arene and one resorcin[4]arene. In a (2+2)-mode of coupling, the combination of calix[4]arenes and resorcin[4]arenes gave a large rigid receptor molecule of nanosize dimensions (ho/and). The combination of two calix[4]arenes with one resorcin[4)arene resulted in three different compounds (endo-endo, endo-exo, and exo-exo) with large hydrophobic surfaces to which steroids can be complexed.