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.