CATENATED CYCLODEXTRINS

A novel synthetic approach is described for the construction of catena nes in aqueous solution from a partially methylated cyclodextrin (CD)- namely, heptakis(2,6-di-O-methyl-beta-cyclodextrin (DM-beta-CD)-and a range of substrate molecules that contain a hydrophobic central core i n the form of a 4,4'-disubstituted biphenyl unit (usually bitolyl) car rying two hydrophilic polyether side chains terminated by primary amin e functions. In water, the amphiphilic catenane precursors form 1:1 co mplexes with beta-CD and DM-beta-CD and 2.1 (guest:host) complexes wit h the larger gamma-CD. Macrocyclizations of the biphenyl-containing su bstrates with aromatic diacid chlorides in aqueous solution and in the presence of DM-beta-CD under Schotten-Baumann conditions afforded-in low yields-a range of [2]- and [3lcatenanes. When a consitutionally as ymmetrical diamine was employed as the substrate, orientational isomer s of a [2]catenane were obtained. A [3]catenene incorporating a macroc yclic tetralactam was found to exist as a mixture of head-to-head and head-to-tail isomers, which could be separated by high pressure liquid chromatography and identified unambiguously by nuclear magnetic reson ance spectroscopy. One of the [2]catenanes afforded good single crysta ls from which the solid state structure was determined by X-ray crysta llography. Other techniques which aided the characterization of these novel compounds included ultraviolet/visible and luminescence spectros copy, dynamic nuclear magnetic resonance spectroscopy and fast atom bo mbardment mass spectrometry. Generally speaking, the catenated cyclode xtrins are soluble in halogenated and aromatic hydrocarbons as well as in hydroxylic solvents. The existence of these new compounds gives us a unique insight into the nature of the noncovalent. bonding interact ions that cyclodextrins employ in binding substrate molecules.