Cell-Permeable Fluorogenic\nProbes for Identification\nand Imaging Nitroreductases in Live Bacterial Cells

Enzyme-activated\nfluorogenic probes, which invoke enzymatic catalysis\nto trigger the generation of fluorescence, provide a versatile platform\nfor monitoring biological processes. The development of fluorogenic\nprobes that can readily penetrate the cell envelopes of bacteria are\nessential to examine intracellular targets of live bacterial cells.\nHerein, we present the design, synthesis, properties, and biological\napplications of two series of fluorogenic probes based on cyanine\n5 for identification of bacterial nitroreductase (NTR). The selected\nfluorogenic probe 3 generates a rapid 10-fold fluorescence\nresponse after being catalytically reduced by NTR to the intermediate para-aminobenzyl substituted which then underwent a rearrangement\nelimination reaction. Moreover, probe 3 is cell permeable\nfor both Gram-positive and Gram-negative bacterial cell envelopes\nand is selective for NTR over other biological analytes, thus minimizing\nthe background signal and enabling the real-time intracellular imaging\nof NTR in live bacterial cells.