1,3-ALTERNATE CALIX[4]ARENECROWN-5 CONFORMERS - NEW SYNTHETIC IONOPHORES WITH BETTER K+ NA+ SELECTIVITY THAN VALINOMYCIN/

New 25,27-dialkoxycalix[4]arenecrown-5 conformers 8, 10, and 11 have b een synthesized and studied. The compounds 8a and 8b, fixed in 1,3-alt ernate structure, have been obtained in 57 and 40% yield, respectively , by reaction of the corresponding 25,27-dialkoxycalix[4]arenes 7a-b w ith tetraethylene glycol di-p-toluenesulfonate in the presence of Cs2C O3. The cone 10a and 10b and the partial cone II conformers were obtai ned by selective demethylation of the 25,27-dimethoxycalix[4]arenecrow n-5 (6a) and subsequent dialkylation with NaH/DMF and KOtBu/THF, respe ctively, In the solid state (X-ray), compound 6a adopts a flattened co ne conformation, which is also found to be most abundant in CD3CN and CD3OD solution. Upon complexation with potassium picrate compound 6a w as converted quantitatively into the 1,3-alternate conformation, All n ew ligands synthesized were used in the extraction of alkali metal cat ions from H2O into CHCl3, and as active components in supported liquid membranes and in chemically modified field effect transistors. Result s were compared to those obtained with with the natural antibiotic val inomycin 1. All ligands showed high selectivity for potassium. Ligand 8 a, fixed in the 1,3-alternate conformation, is more selective than v alinomycin and shows the highest K+/Na+ selectivity known so far.