Two-photon activated precision molecular photosensitizer targeting mitochondria

Modular synthesis of pentacyclic-fused pyranoquinoliziniums as organelle-selective fluorescent probes

On basis of their unique chemical and photophysical properties, and excellent biological activities, quinoliziniums have been widely used in various research fields. Herein, modular synthetic strategies for efficient synthesis of novel fluorescent quinoliziniums by using one-pot and stepwise rhodium(III)-catalyzed C-H annulations were developed. In the one-pot synthesis, the reaction between 2-aryl-4-quinolones (1) and 1,2-diarylalkynes (2) proceeded in a chemo- and regioselective manner to give quinolinone-fused isoquinolines (3) and pentacyclic-fused pyranoquinoliziniums (4). The structural diversity of pentacyclic-fused pyranoquinoliziniums (4) was expanded by the stepwise synthesis from 3 and 2, allowing the strategic incorporation of electron-donating (OMe and OH) and electron-withdrawing (Cl) substituents on the top and bottom parts of the pyranoquinoliziniums (4). These newly synthesized pyranoquinoliziniums (4) exhibited tunable absorptions (455-532 nm), emissions (520-610 nm), fluorescence lifetime (0.3-5.6 ns), large Stokes shifts (up to 120 nm), and excellent fluorescence quantum yields (up to 0.73) upon adjusting the different substituents. The the unique arrangement of N and O atoms and extended π-conjugation of 4 could cause the relocation of HOMO comparing with our previous quinoliziniums. Importantly, pyranoquinoliziniums (4a-4g and 4i) targeted the mitochondria, while 4h was localized in lysosome. Due to the remarkable photophysical properties and the potential for organelle targeting of the novel class of quinoliziniums, they could be further applied for biological, chemical and material applications.

Discrimination of normal and cancerous human skin tissues based on laser-induced spectral shift fluorescence microscopy

A homemade spectral shift fluorescence microscope (SSFM) is coupled with a spectrometer to record the spectral images of specimens based on the emission wavelength. Here a reliable diagnosis of neoplasia is achieved according to the spectral fluorescence properties of ex-vivo skin tissues after rhodamine6G (Rd6G) staining. It is shown that certain spectral shifts occur for nonmelanoma/melanoma lesions against normal/benign nevus, leading to spectral micrographs. In fact, there is a strong correlation between the emission wavelength and the sort of skin lesions, mainly due to the Rd6G interaction with the mitochondria of cancerous cells. The normal tissues generally enjoy a significant red shift regarding the laser line (37 nm). Conversely, plenty of fluorophores are conjugated to unhealthy cells giving rise to a relative blue shift i.e., typically SCC (6 nm), BCC (14 nm), and melanoma (19 nm) against healthy tissues. In other words, the redshift takes place with respect to the excitation wavelength i.e., melanoma (18 nm), BCC (23 nm), and SCC (31 nm) with respect to the laser line. Consequently, three data sets are available in the form of micrographs, addressing pixel-by-pixel signal intensity, emission wavelength, and fluorophore concentration of specimens for prompt diagnosis.

Site-selected thionated benzothioxanthene chromophores as heavy-atom-free small-molecule photosensitizers for photodynamic therapy

Photodynamic therapy is a clinically approved anticancer modality that employs a light-activated agent (photosensitizer) to generate cytotoxic reactive oxygen species (ROS). There is therefore a growing interest for developing innovative photosensitizing agents with enhanced phototherapeutic performances. Herein, we report on a rational design synthetic procedure that converts the ultrabright benzothioxanthene imide (BTI) dye into three heavy-atom-free thionated compounds featuring close-to-unit singlet oxygen quantum yields. In contrast to the BTI, these thionated analogs display an almost fully quenched fluorescence emission, in agreement with the formation of highly populated triplet states. Indeed, the sequential thionation on the BTI scaffold induces torsion of its skeleton reducing the singlet-triplet energy gaps and enhancing the spin-orbit coupling. These potential PSs show potent cancer-cell ablation under light irradiation while remaining non-toxic under dark condition owing to a photo-cytotoxic mechanism that we believe simultaneously involves singlet oxygen and superoxide species, which could be both characterized in vitro. Our study demonstrates that this simple site-selected thionated platform is an effective strategy to convert conventional carbonyl-containing fluorophores into phototherapeutic agents for anticancer PDT.

Functionalized quinolizinium-based fluorescent reagents for modification of cysteine-containing peptides and proteins

A series of quinolizinium-based fluorescent reagents were prepared by visible light-mediated gold-catalyzed cis-difunctionalization between quinolinium diazonium salts and electron-deficient alkyne-linked phenylethynyl trimethylsilanes. The electron-deficient alkynyl group of the quinolizinium-based fluorescent reagents underwent nucleophilic addition reaction with the sulfhydryl group on cysteine-containing peptides and proteins. The quinolizinium-based fluorescent reagents were found to function as highly selective reagents for the modification of cysteine-containing peptides and proteins with good to excellent conversions (up to 99%). Moreover, the modified BCArg mutants bearing cationic quinolizinium compounds 1b, 1d, 1e and 1h exhibit comparable activity in enzymatic and cytotoxicity assays to the unmodified one.

New quinolizinium-based fluorescent reagents were made by visible light-mediated gold-catalyzed cis-difunctionalization of quinolinium diazonium salts and trimethylsilyl alkyne derivatives.