BODIPY-Based Profluorescent Probes Containing Meso- and β-Substituted Isoindoline Nitroxides

BODIPY is a highly versatile fluorophore for biological imaging with a tunable fluorescence emission (500-800 nm) that overlaps the optically transparent window for tissue ( 6001300 nm). Herein, we describe the synthesis of optically distinct BODIPY-based profluorescent probes bearing meso- and beta-substituted isoindoline nitroxides and their corresponding methoxyamine derivatives. These profluorescent nitroxide probes possess strongly suppressed fluorescence, which can be revealed upon reduction or reaction with other radicals. Examination of the pentafluorophenylhydrazine reduction of the pre-pared probes by using tandem electron paramagnetic resonance (EPR) and fluorescence spectroscopy demonstrated that the asymmetric bis-beta-substituted probe 9 (lambda(em) = 603 nm) was reduced the fastest; however, the greatest difference in fluorescence emission between the nitroxide and its reduced hydroxylamine analogue was observed for probe 7 (lambda(em) = 570 nm). The significant difference in fluorescence output between the nitroxides and their corresponding diamagnetic derivatives makes these probes ideal tools for imaging reactive oxygen species in biological systems.