Bis-benzoboroxole-type glucose receptor with anthracene fluorophore

We synthesized a bis-benzoboroxole-type glucose receptor (bis-BB-AN) in which the glucose recognition site of the bis-phenylboronic acid receptor with anthracene fluorophore (bisPBA-AN), which is known as an excellent glucose receptor, was replaced with benzoboroxole (BB). The glucose recognition abilities of these bis-PBA-AN and bis-BB-AN receptors were evaluated on the basis of the alizarin red S (ARS) colorimetric assay and the fluorescence assay. The complex formation constant with glucose estimated by the ARS colorimetric assay was 0.6 mol^–1 L for the bis-PBA-AN receptor, and 30 mol^–1 L for the bis-BB-AN receptor, respectively: The large complex formation constant of the bis-BB-AN receptor compared to the bis-PBA-AN receptor reflects the higher glucose recognition ability of BB than that of PBA. However, the complex formation constant with glucose estimated by the fluorescence assay was 3600 mol^–1 L for bis-PBA-AN and 170 mol^–1 L for bis-BB-AN: The bis-PBA-AN receptor showed an ~20-times greater glucose recognition ability than the bis-BB-AN receptor. These results suggest that the excellent glucose recognition ability of bis-PBA-AN is due to the glucose-specific fluorescence switching mechanism during weak binding, rather than to the ability to form a stable complex with glucose.