BODIPY fluorescent probes

Guminski Y, Grousseaud M, Cugnasse S et al (2009) Synthesis of conjugated spermine derivatives with 7-nitrobenzoxadiazole (NBD), rhodamine and bodipy as new fluorescent probes for the polyamine transport system. Bioorg Med Chem Lett 19 2474—2477... 

Fluorescence imaging is the most powerful technique currently available for continuous observation of the dynamic intracellular processes of living cells. Fluorescein is widely employed as the core of various fluorescence probes used in imaging important biological effectors. Despite the extensive use of fluorescein derivatives and the importance of the applications, the mechanism that controls the quantum yield of fluorescence has not been fully established. I report herein photoinduced electron transfer (PeT) mechanism that can control the fluorescence quantum yields of fluorescein and boron dipyrromethene (BODIPY) derivatives. 

Figure 3. Novel BODIPY-based fluorescence probes...

Novel fluorescence probes for nitric oxide (DAMBO-P ) and for Zn " (ZnAB) have been developed based on BODIPY structure (Fig. 3). DAMBO-P is a pH-independent and more highly sensitive fluorescence probe for nitric oxide than DAF-2. ZnAB has the advantages of less sensitivity to solvent polarity and pH than ZnAF-2, fluorescein-based Zn " probe, and is also not influenced by other cations such as Na", K, Ca and Mg, which exist at high concentration under physiological conditions. 

The results obtained are consistent with our hypothesis that the fluorescence properties of fluorescein and BODIPY derivatives are determined by a PeT process from the benzoic acid moiety. This provides a practical strategy for rational design of functional fluorescence probes to detect certain biomolecules and developed probes should be widely useful in biological systems from the point of sensitivity and specificity. 

NBD fluorescent probe 87 was prepared from condensation between free amino derivative (S)-85 (n = 5) and NBD chloride in 76% yield. BODIPY derivative 88 was obtained starting from a condensation between the compound (5)-85 ( = 5) and BODIPY N-succinimidyl ester in 72% yield (Scheme 20). 

Scheme 11.1 Structure of three organic fluorophores classically used as fluorescent probes, (a) Fluorescein, (b) Rhodamine 123. (c) BODIPY.

BODIPY fluorescence (Figure 31). These particular properties minimize the background signal and lead to a better tumor-to-normal tissue signal ratio in fluorescence microscopy imaging experiments (Figure 32). The process was also shown to be reversible and, after treatment of tumors with ethanol, the fluorescence disappeared. Since this probe turns off when the cells die, this fluorescence... 

With the same mechanism, a series of unique, acidic pH-sensitive fluorescence probes have been eonstructed for bioimaging viable cancer eells (Scheme 7.9). All these bear various anilines at the meso-position of the BODIPY fluorophore. Similarly, they are almost non-fluorescent in the non-protonated form due to the efficient PET from the aniline moiety to the BODIPY fluorophore. In contrast, they are protonated in acidic medium, and become highly fluorescent, along with a 300-fold increase in emission. With these promising features in hand, fluorescence turn-on probe-antibody eonjugates have been successfully exploited in specific imaging of viable eaneer eells. 

The development of fluorescent probes for detection of reactive oxygen species (ROS) has become an active research field. Probe 30 is a BODIPY-based probe bearing the reaction site of o-phenylenediamine toward NO. It shows fluorescence at 500 nm with low quantum yield due to the PET mechanism. The conversion of o-phenylenediamine into a benzotriazole group upon reaction with NO elicits a remarkable fluorescence enhancement (Scheme 7.26). 

Meijler et al. reported the visualization of specific native proteins in live cells through a two-step labeling strategy, using a combination of isothiocyanate and oxime chemistry. The established labeling process involves an aniline-catalyzed oxime formation between the modified receptor and a fluorescent BODIPY derivative (probe 38, Scheme 7.33), which is expected to show potential in exploration of the intracellular ligation of other types... 

The building block of BODIPY can be well tailored by structural modification, enriching the family of BODIPY dyes. Indeed, the BODIPY scaffold serves as a promising platform for the construction of molecular sensors. Given that BODIPY derivatives bear excellent characteristics, such as intense fluorescence quantum yields, sharp absorption and fluorescence emission spectra, a tremendous expansion has been witnessed in BODIPY-based probes for versatile applications. The established BODIPY-based probes always exhibit fluorescence turn-on or ratiometric responses to a target, by making full use of photophysical processes with common channels such as PET, ICT or FRET. There is no doubt that the rational construction of BODIPYs with these photophysical features still serves as effective strategies to further develop powerful probes or chemodosimeters. 

The current understanding of synthesis and photophysical properties of 4,4-difluoro-4-bora-3a,4a-diaza-s-indaeene derivatives (BODIPY dyes) and their important applieations for moleeular sensors are described by Zhu and Zhao. The often eomplieated synthetie routes required for the preparation of BODIPY derivatives has restrieted their use as fluorescent reagents. However, Chapter 7 deseribes up-to-date methods for the preparation of many BODIPY derivatives. In addition, reeent advances of using BODIPYs as signaling units for fluorescent probes seleetive towards different analytes are presented. 

An emulsion of E7, a common nematic liquid crystal, in an aqueous solution of poly (vinyl alcohol) (PVA) was deposited onto the sur ce of an inditun-tin-oxide (ITO) coated substrate. The ITO coating provided a transparent conducting surface that formed the counter-electrode to the biased NSOM tip. Polarized light NSOM experiments were performed on both pure E7 droplets and those doped with the fluorescent probe molecule BODIPY.(Mei et al. 2000)... 

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