MOLECULAR RECOGNITION BY NOVEL CAGE-TYPE AZAPARACYCLOPHANES BEARING CHIRAL BINDING-SITES IN AQUEOUS-MEDIA

Novel cage-type cyclophanes which are constructed with two rigid macrocyclic skeletons, tetraaza[6.1.6.1]paracyclophane and tetraaza[3.3.3.3]-paracyclophane, and four chiral bridging components were prepared. An asymmetric character of the internal cavity was clarified by means of circular dichroism (CD) spectroscopy and a computer-aided molecular modeling study based on molecular mechanics and dynamics (BIOGRAF, Dreiding-I and Dreiding-II) conformational search. In aqueous media, the present hosts strongly bound anionic and nonionic hydrophobic guests to form inclusion complexes in 1:1 stoichiometry and the CD phenomena were induced in an incorporated achiral guest molecule through its stereochemical interaction with the chiral host cavity. In addition, the present hosts exhibited discriminative recognition toward steroid hormones in D2O/CD3OD (3:1 v/v) as effected by hydrophobic and pi-pi interactions. The chirality-based discrimination of estrogens was attributed to their different modes of hydrogen bonding with the hosts.