A new glucose-selective fluorescent bisboronic acid.: First report of strong α-furanose complexation in aqueous solution at physiological pH

A new bisboronic acid based glucose sensor 7 was synthesized from 9,10-bis(chloromethyl)anthracene and 2,2-dimethyl-1,3-propanediol protected 3-pyridineboronic acid. Due to its ionic structure 7 was found sufficiently water soluble for carbohydrate binding studies at neutral pH by means of NMR spectroscopy, fluorometry, and potentiometry. The pK(a)'s of 7 have been determined to 3.7 and 4.7 by potentiometric titration. From a solution of 7 and glucose (1:1) in water (pH 7.4) we observed the formation of a bisdentate boronic acid complex 7.Glu which has been assigned to a 1,2:3,5 bound alpha-D-glucofuranose complex. The evidence for this furanose structure comprises H-1 and C-13 NMR data with emphasis on the information from (1)J(C-C) coupling constants. Complex 7 Glu shows an increased fluorescence compared to 7. The stability constant for the 1:1 complex (log K = 3.4) was determined from fluorometric titration, potentiometry, and NMR spectroscopy. Boronic acid 7 shows good selectivity for glucose compared to fructose and galactose.