Imidazole-capped 3-cyclodextrins

The effect of the hydrophobic cyclodextrin cavity of 7 was enhanced and the lifetime of the 7-oxygen adduct was prolonged to about 1 hr in the aqueous medium at —10 °C when a drop of benzene was dispersed in the aqueous medium of the deoxy-7 imidazole complex. The benzene was probably occluded in the cavity of the capping cyclodextrin However, the life-time decreased with temperature of the aqueous medium and the oxygen adduct was scarcely observed above 0 C. The steric and... 

Either the C -capped or the O -capped material can be heated with an excess of imidazole to produce /3-cyclodextrin bisimidazole (VII). On the basis of the above discussion, we believe that the material produced from the C-capped compound is a 6A,6C and 6A,6D isomeric mixture, while that produced from the O-capped compound is largely the 6A,6D isomer. As it turns out, we have not detected yet significant differences between these two materials as catalysts in our kinetic and product studies. 

On treatment with potassium iodide, the capped disulfonate j8-cyclo-dextrin discussed above could easily be converted to the corresponding diiodide jS-cyclodextrin. With appropriate nucleophiles (imidazole, histamine) a new route to bis(iV-imidazolyl)-j8-cyclodextrin and bis(iV-histamino)-j8-cyclodextrin was developed by Tabushi s team (182). In the presence of Zn(II) ion, both regiospecifically bifunctionalized cyclodextrins hydrate CO2 and are the first successful carbonic anhydrase models. The Zn(II) ion binds to the imidazole rings located in the edge of the cyclodextrin pocket and the presence of an additional basic group, as with bis(histamino)-cyclodextrin-Zn(II), enhances the activity. Therefore, the present models show that all three factors, Zn(II)-imidazole, hydrophobic environment, and a base seem to help to generate the carbonic anhydrase activity (182). The chemistry of this enzyme is further discussed in Section 6.2, p. 331. 

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