Structure activity studies of nitroreductase‐responsive near‐infrared heptamethine cyanine fluorescent probes

Two new classes of near-infrared molecular probes were prepared and shown to exhibit “turn on” fluorescence when cleaved by the nitroreductase enzyme, a well-known biomarker cell hypoxia. The fluorescent are heptamethine cyanine dyes with central 4‘-carboxylic ester group on chain that is converted self-immolative fragmentation mechanism 4‘-caboxylate greatly enhances brightness. Each compound was ring opening Zincke salt. chemical structures have either terminal benzoindolinenes or propargyloxy auxochromes, which provide favorable red-shifted absorption/emission wavelengths hyperchromic effect photon output excited 808 nm light. A probe propargyloxy-indolenines exhibited less self-aggregation rapidly activated large on“ fluorescence; thus, it preferred choice for translation towards in vivo applications.