Sugar-induced Stereoselectivity in the Fe3+-complexation of Boronic Acid-appended Trihydroxamate-type Artificial Siderophores

Two linear- and two tripodal-trihydroxamate siderophore mimics, suspending phenylboronic acid as the sugar-binding site, have been newly prepared. These siderophore mimics strongly bind Fe3+ ions to give rise to the ligand-Fe3+ 1:1 complexes over a wide range of pH 2 to 11. Circular dichroism (CD) spectra of these complexes in the presence of a sugar, D-fructose, exhibit moderately strong bisignate Cotton effects of first negative and second positive signs in aqueous alkaline media. The sign and extent of the observed CD signals depend largely on the solution pH and the concentration and absolute configuration of the bound sugars, implying that the phenylboronate-sugar covalent interactions are capable of inducing a chirality around the metal center.