Highly selective lipophilic diboronic acid that transports fructose as the trisdentate 2,3,6-β-d-fructofuranose ester

The transport of fructose and glucose through supported liquid membranes promoted by a tetrahedral shaped lipophilic monoboronic acid and diboronic acid, both based on a pentaerythritol core, has been studied. The diboronic acid gave a high fructose/glucose selectivity (7.7:1.0). The results of molecular modelling studies and 13C NMR experiments with uniformly labelled 13C-d-fructose suggest that the enhanced selectivity results from the formation of a trisdentate 2,3,6-β-d-fructofuranose diester within the membrane. Experimental evidence for a previously proposed macrocyclic d-fructopyranose diester formed with an o-phenylene linked diboronic acid has also been found.