Syntheses of 2-NBDG analogues for monitoring stereoselective uptake of D-glucose.

2-NBDG is a widely used fluorescent tracer for monitoring d-glucose uptake into single living cells. However, 2-NBDG alone is not sufficient for monitoring the net stereoselective uptake of d-glucose, unless its possible non-stereoselective uptake is properly evaluated. l-Glucose derivatives, which emit fluorescence distinct from that of 2-NBDG, should provide valuable information on the stereoselective uptake, when used with 2-NBDG in combination. In the present study, we synthesized Texas Red (sulforhodamine 101 acid)-coupled and [2-(benz-2-oxa-1,3-diazol-4-yl)amino]-coupled 2-deoxy-d-glucose, referred to as [2-TRG] and [2-BDG], respectively. These derivatives showed emission wavelength longer and shorter than that of 2-NBDG, respectively. 2-TRLG, an antipode of 2-TRG, proved to be an effective tracer for evaluating the extent of non-stereoselective uptake of 2-NBDG when used simultaneously with 2-NBDG. On the other hand, 2-BDG exhibited very weak fluorescence, but the application of a novel cross coupling in the presence of a benzoxadiazole group may be useful for the future development of effective glucose tracers.