beta -Helical polymers from isocyanopeptides.

Polymerization of isocyanopeptides results in the formation of high molecular mass polymers that fold in a proteinlike fashion to give helical strands in which the peptide chains are arranged in beta-sheets. The beta-helical polymers retain their structure in water and unfold in a cooperative process at elevated temperatures. The peptide architecture in these polymers is a different form of the beta-helix motif found in proteins. Unlike their natural counterparts, which contain arrays of large beta-sheets stacked in a helical fashion, the isocyanopeptide polymers have a central helical core that acts as a director for the beta-sheet-like arrangement of the peptide side arms. The helical structure of these isocyanopeptide polymers has the potential to be controlled through tailoring of the side branches and the hydrogen-bonding network present in the beta-sheets.

Water-soluble adamantane-terminated dendrimers possessing a rhenium core.

A novel type of radiometal-containing dendrimer with potential radiotherapeutical applications is described. Different generations of this adamantane-terminated, Fréchet-type dendrimer (28, 29, 30), each consisting of two dendritic wedge ligands around a rhenium core, have been synthesized in organic solvent via reaction with ReO(PPh(3))(2)Cl(3). Through complexation of their adamantane groups by beta-cyclodextrins (beta-CDs), these dendrimers were made water soluble (9.6, 0.4, and 0.2 mM, respectively). beta-CD-induced solubilization of the wedges in water allowed the complexes to be made under aqueous conditions, via reaction with rhenium gluconate. Not only does this strategy enable the facile synthesis of the radioactive analogue, the yields for these complex-formation reactions in water also turned out to be far higher than those observed for the reactions in organic solvents.

Complexation and (templated) synthesis of rhenium complexes with cyclodextrins and cyclodextrin dimers in water.

Several small, lipophilic rhenium complexes form inclusion complexes with native beta-cyclodextrin (beta-CD) and beta-CD dimers. Association constants larger than 10(9)M(-1) were obtained using dimers. The use of beta-CD also enabled the synthesis of these rhenium complexes in water, in excellent yields, through complexation of the otherwise insoluble corresponding ligands. The influence of the reaction time and temperature on the configuration of the reaction products has been investigated in depth for one of these complexes. Using a beta-CD dimer, it proved possible to specifically template the formation of one configuration. The strength of the complexes of the rhenium complexes in cyclodextrin dimers may allow radiolabeling of biomolecules.