Specific complexation of glucose with a diphenylmethane-3,3′- diboronic acid derivative: Correlation between the absolute configuration of mono- and di-saccharides and the circular dichroic activity of the complex

For the development of receptor molecules that can precisely recognize sugar molecules, we recently synthesized bis-(6-methoxyphenyl)methane-3, 3′-diboronic acid 2. This compound forms 1:1 complexes with mono- and di-saccharides and gives circular dichroism (CD) spectra specific to each saccharide. It was shown on the basis of ¹H NMR spectroscopy that the complex with D-glucose is a macrocyclic compound formed by the reaction of the two boronic acids with c/s-1,2-diol and trans-4-OH, 5-CH₂OH moieties. Thus, compound 2 becomes CD-active because of asymmetric immobilization of the two chromophoric benzene rings by ring closure with chiral saccharides. The association constants were in the following order: D-glucose (19 000 dm ³ mol^-1) ≥ D-talose > D-galactose > D-mannose > D-fructose (= 0 dm³ mol^-1) for monosaccharides, and D-maltose (100 dm³ mol^-1) > D-cellobiose > D-lactose > D-saccharose (= 0 dm³ mol^-1) for disaccharides. In particular, compound 2 showed a very high affinity toward D-glucose. D-Glucose gave a CD spectrum with positive exciton coupling whereas L-glucose gave a CD spectrum with negative exciton coupling. D-Galactose gave a CD spectrum with negative exciton coupling, whereas all other D-mono- and D-disaccharides tested herein gave CD spectra with positive exciton coupling. The results indicate that the absolute configuration of saccharides can be conveniently predicted from the sign and the strength of the CD spectra of their complex with compound 2. This means that the CD spectroscopic method using compound 2 as a receptor probe serves as a new sensory system for sugar molecules.