Fructose controlled ionophoric activity of a cholate-boronic acidElectronic supplementary information (ESI) available: NMR spectra of 3. K+ transport by 3. U-tube picrate transport data. Effect of fructose on Na+ transport by 3 or 4. See DOI: 10.1039/c4ob00165f

Wulff-type boronic acids have been shown to act as ionophores at pH 8.2 by transporting Na + through phospholipid bilayers. A cholate-boronic acid conjugate was synthesised and shown to be an ionophore, although the hydroxyl-lined face of the cholate moiety did not enhance ion transport. Mechanistic studies suggested a carrier mechanism for Na + transport. The addition of fructose (>5 mM) strongly inhibited ionophoric activity of the cholate-boronic acid conjugate, mirrored by a strong decrease in the ability of this compound to partition into an organic phase. Modelling of the partitioning and ion transport data, using a fructose/boronic acid binding constant measured at pH 8.2, showed a good correlation with the extent of fructose/boronic acid complexation and suggested high polarity fructose/boronic acid complexes are poor ionophores. The sensitivity of ion transport to fructose implies that boronic acid-based antibiotic ionophores with activity modulated by polysaccharides in the surrounding environment may be accessible. The transport of Na + through phospholipid bilayers by Wulff-type boronic acids at pH 8.2 is reported. Concentrations of fructose greater than 5 mM strongly inhibited ionophoric activity.