Construction of Functional Molecules Using Cholic Acid as a Building Block

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(1) Synthesis of bicyclocholaphanes and their recognition abilities.The aim of this research project is to prepare novel host compounds usings cholic acids, the cheap easily available steroid, as a building block for the selective recognition of biologically important molecules. The following three topics were investigated.By employing its characteristic features, the rigid L-shaped molecule with three hydroxyl groups on its inner surface, bicyclocholaphanes with several cavity sizes were prepared. They showed reasonable extractability toward ribonucleosides and sugars in liquid (chloroform) - liquid (water) extraction. Strong binding constants (10^4M^<-1>) were obtained for ribonucleoside in solid - liquid (chloroform) extraction by them. AZT, an important anti-viral agent especially for AIDS, was included inside the cavities of cholaphanes, which was characterized by ^1H-NMR titration.2) Comparison of recognition abilities of bicyclocholaphanes with the corresponding tripodants.Whether cyclic structures were really necessary as a potential host molecules, the tripodant-type host molecules possessing three cholic acid units attached to cyclotribenzylene (a rigid molecules) and trimesic acid were prepared and their recognition abilities toward nucleosides were examined. Roughly speaking, these tripodants showed poor recognition abilities except few cases. It seems to be these tripodants have too flexible conformations so that they cannot bind guest molecules well.(3) Synthesis of bicyclochopahanes with metal complex formation.The novel ligand possessing three cholic acid units and bipyridyl at the end was prepared for the formation of bicyclocholaphane by complex formation with ruthenium. The complex was characterized by its ESI-MS and absorption spectrum.