Molecular Design of Highly Selective and Sensitive “Sugar Tweezers” from Boronic Acid-Appended μ-Oxo-bis[porphinatoiron(III)]s

Abstract 5,10,15,20-Tetrakis[3- and 4-(dihydroxyboryl)phenyl]porphinatoiron(III)s (1a and 1b, respectively) were synthesized and the saccharide-binding ability of their μ-oxo dimers was investigated. The saccharide-binding process with boronic acids can be conveniently monitored by CD spectroscopy. The μ-oxo dimer of 1b with 4-(hydroxyboryl) groups can bind glucose and galactose among monosaccharides with extremely high selectivity and sensitivity (association constants 104—105 dm3 mol−1), whereas that of 1a with 3-(hydroxyboryl) groups shows only a weak affinity with these monosaccharides. A similar trend was also observed for disaccharides. The origin of the CD activity in 2b can be ascribed to the formation of 1 : 1 μ-oxo dimer/saccharide complexes, in which two porphyrin rings are chirally bridged by one saccharide molecule. The CD sign is well-correlated with the absolute configuration of these saccharides. Thus, the present paper demonstrates that the μ-oxo dimer of 1b, which is formed in a self-assembled manner in aqueous alkaline solution, acts as an excellent pair of artificial “sugar tweezers”.