Synthesis and fluorescence properties of red-to-near-infrared-emitting push-pull dyes based on benzodioxazole scaffolds

A dual-functional photosensitizer for mitochondria-targeting photodynamic therapy and synchronous polarity monitoring

Mitochondria-targeting photodynamic therapy (PDT) has been validated as an effective strategy for inducing cell death through the disruption of mitochondrial function. The mitochondrial microenvironment, such as viscosity, polarity, pH and proteins, undergoes dynamic changes during PDT treatment, and investigating these parameters is crucial for comprehending the intrinsic mechanisms at the cellular level. In this context, disclosure of mitochondrial microenvironment alterations holds significant importance. Nevertheless, a probe capable of visualizing mitochondrial polarity fluctuations during PDT treatment has not been reported. Importantly, a dual-functional photosensitizer (PS) with polarity detection capability is highly advantageous as it can mitigate potential metabolic and localization disparities between the PS and the polarity probe, thus improving the accuracy of detection. In this contribution, a series of potential PSs were prepared by integrating the 2,1,3-benzoxadiazole (BD) scaffold with various heteroatom-incorporated electron-withdrawing groups. Among them, BDI exhibited potent phototoxicity against cancer cells and remarkable sensitivity to polarity changes, establishing it as a dual-functional PS for both photodynamic therapy and polarity detection. Leveraging its polarity detection capability, BDI successfully discriminated mitochondrial polarity discrepancy between cancer cells and normal cells, and indicated mitochondrial polarity fluctuations during drug-induced mitophagy. Crucially, BDI was employed to unveil mitochondrial polarity variations during PDT treatment, underscoring its dual function. Altogether, the meticulous design of the dual-functional PS BDI offers valuable insights into intracellular microenvironment variations during the PDT process, thereby enhancing our understanding and guiding the optimization of PDT treatment.

Novel pyrrolidine-alkylamino-substituted dicyanoisophorone derivatives as near-infrared fluorescence probe for imaging β-amyloid in vitro and in vivo

BACKGROUND

The formation of amyloid-β (Aβ) plaques is one of the key neuropathological hallmarks of Alzheimer's disease (AD). Near-infrared (NIR) probes show great potential for imaging of Aβ plaques in vivo and in vitro. Dicyanoisophorone (DCIP) based Aβ probes have attracted considerable attention due to their exceptional properties. However, DCIP probes still has some drawbacks, such as short emission wavelength (<650 nm) and low fluorescence intensity after binding to Aβ. It is clear that further modification is needed to improve their luminescence efficiency and sensitivity.

RESULTS

We designed and synthesize four novel pyrrolidine-alkylamino-substituted DCIP derivatives (6a-d) as imaging agents for β-amyloid (Aβ) aggregates. Compound 6c responds better to Aβ aggregates than the other three compounds (6a, 6b and 6d) and its precursor DCIP. The calculated detection limit is to be as low as 0.23 μM. Compound 6c shows no cytotoxicity in the tested concentration for SH-SY5Y and HL-7702 cells. Additionally, compound 6c is successfully applied to monitor Aβ aggregates in live SH-SY5Y cells and APP/PS1 transgenic mice. The retention time in the transgenic mice brain is much longer than that of age-matched wild-type mice.

SIGNIFICANCE

The results indicates that compound 6c had an excellent ability to penetrate the blood-brain barrier and it could effectively distinguish APP/PS1 transgenic mice and wide-type mice. This represents its promising applications for Aβ detection in basic and biomedical research.

Julolidine-based small molecular probes for fluorescence imaging of RNA in live cells

Intracellular RNA imaging with organic small molecular probes has been an intense topic, although the number of such reported dyes, particularly dyes with high quantum yields and long wavelength excitation/emission, is quite limited. The present work reports the design and synthesis of three cationic julolidine-azolium conjugates (OX-JLD, BTZ-JLD and SEZ-JLD) as turn-on fluorescent probes with appreciably high quantum yields and brightness upon interaction with RNA. A structure-efficiency relationship has been established for their potential for the interaction and imaging of intracellular RNA. Given their chemical structure, the free rotation between the donor and the acceptor gets restricted when the probes bind with RNA resulting in strong fluorescence emission towards a higher wavelength upon photoexcitation. A detailed investigation revealed that the photophysical properties and the optical responses of two probes, viz. BTZ-JLD and SEZ-JLD, towards RNA are very promising and qualify them to be suitable candidates for biological studies, particularly for cellular imaging applications. The probes allow imaging of intracellular RNA with prominent staining of nucleoli in live cells under a range of physiological conditions. The results of the cellular digest test established the appreciable RNA selectivity of BTZ-JLD and SEZ-JLD inside the cellular environment. Moreover, a comparison between the relative intensity profile of SEZ-JLD before and after the RNA-digestion test inside the cellular environment indicated that the interference of cellular viscosity in fluorescence enhancement is insignificant, and hence, SEZ-JLD can be used as a cell membrane permeable cationic molecular probe for deep-red imaging of intracellular RNA with a good degree of selectivity.

Palladium-catalyzed C-H dimethylamination of 1-chloromethyl naphthalenes with N,N-dimethylformamide as the dimethyl amino source

Palladium-catalyzed remote C-H dimethylamination of 1-chloromethylnaphthalenes using N,N-dimethylformamide as the dimethylamino source is described for the first time. The dimethylamination took place exclusively at the 4-position of 1-chloromethylnaphthalenes in 2-methyltetrahydrofuran under mild conditions to afford 1-(N,N-dimethylamino)-4-alkylnaphthalenes in good to high yields. The halogen atom remained intact during the dimethylamination of 1-chloromethylnaphthalenes. A P,N bidentate ligand was conveniently synthesized and successfully utilized as the ligand in the Kumada-Corriu reaction.

A biotin-guided near-infrared fluorescent probe for imaging hydrogen sulfide and differentiating cancer cells

Imaging cancer specific biomarkers with near-infrared (NIR) fluorescent probes can help inaccurate diagnosis. Hydrogen sulfide (H₂S) has been reported to be involved in many physiological and pathological processes and is considered as one of the key gasotransmitters during the development of cancer. To achieve specific H₂S detection in cancer cells, we reported a biotin-guided NIR fluorescent sensor P1 targeting a cancer cell surface biomarker, based on the H₂S-specific thiolysis of the NBD-amine-hemicyanine conjugate. The probe showed a fast turn-on signal at 754 nm upon H₂S activation and good selectivity towards H₂S over millimolar levels of other biothiols. We successfully employed P1 to image endogenous H₂S and demonstrated its tumor-targeting ability in live cells. P1 could differentiate multiple cancer cells with various levels of H₂S from normal cells, indicating its potential for cancer imaging.