Xingming Gao

A glucose-selective fluorescence sensor based on boronicacid-diol recognition

A glucose selective diphenylboronic acid fluorescent sensor (10a) with a K(a) of 1472M(-1) has been synthesized and evaluated. This sensor shows a 43- and 49-fold selectivity for glucose over fructose and galactose, respectively. The binding affinity improvement is about 300-fold and the selectivity improvement for glucose over fructose is about 1400-fold compared with the monoboronic acid compound, phenylboronic acid. 1H NMR studies indicate that sensor 10a binds with alpha-D-glucofuranose in a bidentate manner (1:1 ratio).

Diboronic acids as fluorescent probes for cells expressing sialyl lewis X

A series of fluorescent diboronic acids was synthesized in nine steps as potential sensors for sialyl Lewis X (sLex). The fluorescent binding studies of these sensors with sLex were carried out in a mixed aqueous solution. Compound 7e was found to show the strongest fluorescence enhancement upon binding with sLex. Using cell cultures, 7e was shown to label sLex-expressing HEPG2 cells at 1 microM, while non-sLex-expressing cells were not labeled.

Naphthalene-based water-soluble fluorescent boronic acid isomers suitable for ratiometric and off-on sensing of saccharides at physiological pH

Two water-soluble naphthalene-based fluorescent boronic acid isomers, 5-(dimethylamino)naphthalene-1-boronic acid (5-DMANBA, 1) and 4-(dimethylamino)naphthalene-1-boronic acid (4-DMANBA, 2), have been synthesized; their fluorescent properties upon binding with carbohydrates have been determined in aqueous phosphate buffer at pH 7.4. The difference in substitution pattern between 1 and 2 leads to significant differences in their fluorescence properties. For example, addition of fructose (50 mM) to a solution of 1 induced a 61% fluorescence intensity decrease at 513 nm and a 36-fold increase at 433 nm. This revealed that compound 1 is a potential sensor for ratiometric sensing of sugars. The pH titration curves of 1 in the absence and the presence of fructose (50 mM) showed a 93- and 200-fold fluorescence intensity increase at 433 nm, respectively, when pH was increased from 3 to 10. Compound 2, however, does not show ratiometric fluorescent intensity changes, but shows significant fluorescence intensity increase upon addition of a sugar (41-fold intensity increase with 50 mM fructose). The emission intensity of 2 increased by over 170-fold at 445 nm upon changing the pH from 2 to 11.

Catechol pendant polystyrene for solid-phase synthesis

A catechol pendant polystyrene polymer was prepared from the Merrifield resin via a convenient procedure with high-density loading. Due to the high affinity binding between catechol and boronic acid, the polymer resin readily captures boronic acid compounds. The feasibility of using immobilized catechol to capture boronic acid products for purification and solid-phase transformation was demonstrated. Moreover, the immobilized catechol was also used for the preparation of resin-bound catecholborane, which can be used as a solid-phase amidation reagent.

A fluorescent bisboronic acid compound that selectively labels cells expressing oligosaccharide Lewis X.

Two fluorescent diboronic acid compounds (6a and 6b) with a dipeptide linker were synthesized as potential sensors for cell surface saccharide Lewis X (Le(X)). Compound 6a with a dipeptide (H-Asp-Ala-) as the linker was found to selectively label CHOFUT4 cells, which express Le(x), at micromolar concentrations, while non-Le(x)-expressing control cells were not labeled.