MODIFICATION OF A BORONIC ACID CLEFT PRODUCES A SODIUM-SACCHARIDE COTRANSPORTER

An artificial receptor molecule, which fixes a boronic acid and carboxylic acid in a cleft-like orientation 5.5 Angstrom apart, was synthesized and characterized by spectroscopic and X-ray crystallographic methods. Further synthetic studies demonstrated how this cleft compound can be elaborated into more complicated receptors having a variety of recognition capabilities. Specifically, the cleft was conjugated with a crown ether moiety to produce the first example of a new class of artificial sodium-saccharide cotransporter. U tube transport experiments showed this carrier was able to simultaneously bind and cotransport Na+ and p-nitrophenyl beta-D-glucopyranoside through bulk, liquid organic membranes. At pH 6.3, the carrier did not significantly facilitate glucoside transport compared to a control system where the carrier was absent. However, at pH 11.0, transport enhancement increased to five times the background level. This enhancement was considerably better than that observed for a carrier admixture of phenylboronic acid and benzo-15-crown-5. Facilitated active glucoside transport was achieved from a departure phase containing 0.06 mM glucoside and 500 mM sodium phosphate into a receiving phase containing an equal initial glucoside concentration but only 10 mM sodium phosphate.