Asymmetric and Reduced Xanthene Fluorophores: Synthesis, Photochemical Properties, and Application to Activatable Fluorescent Probes for Detection of Nitroreductase

Abstract

Xanthene fluorophores, including fluorescein, rhodol, and rhodamines, are representative classes of fluorescent probes that have been applied in the detection and visualization of biomolecules. “Turn on” activatable fluorescent probes, that can be turned on in response to enzymatic reactions, have been developed and prepared to reduce the high background signal of “always-on” fluorescent probes. However, the development of activity-based fluorescent probes for biological applications, using simple xanthene dyes, is hampered by their inefficient synthetic methods and the difficulty of chemical modifications. We have, thus, developed a highly efficient, versatile synthetic route to developing chemically more stable reduced xanthene fluorophores, based on fluorescein, rhodol, and rhodamine via continuous Pd-catalyzed cross-coupling. Their fluorescent nature was evaluated by monitoring fluorescence with variation in the concentration, pH, and solvent. As an application to activatable fluorescent probe, nitroreductase (NTR)-responsive fluorescent probes were also developed using the reduced xanthene fluorophores, and their fluorogenic properties were evaluated.

Rapid differentiation between bacterial infections and cancer using a near-infrared fluorogenic probe

“…9 We were in particular interested in investigating activatable molecular probes for the detection of nitroreductases (NTRs) in bacteria. [10][11][12][13][14][15] NTRs represent a family of avin-containing enzymes that are able to effectively metabolize nitrosubstituted groups into hydroxylamines or amines in the presence of reduced nicotinamide adenine dinucleotide (NADH) or nicotinamide adenine dinucleotide phosphate (NADPH). 16 NTRs are widely expressed in most Gram-positive and Gramnegative bacterial strains, but also in hypoxic tumour cells and tumorous tissues of eukaryotes.…”

A coumarin derivative-Cu2+ complex-based fluorescent chemosensor for detection of biothiols

“…It exhibits a characteristic emission band peaked at 536 nm, with a uorescence quantum yield (F) of 0.11 calculated using uorescein in 0.1 N NaOH (F ¼ 0.85) as a ref. 50. When 1 equivalent of Cu 2+ was added to the BDC solution, the uorescence intensity of the solution was almost completely quenched, over 95%.…”

Coumarin-Based Dual Chemosensor for Colorimetric and Fluorescent Detection of Cu2+in Water Media

“…The fluorescence quantum yield (Φ) of free probe 5 in aqueous solution is determined to be 10.5%, using the fluorescein in 0.1 N NaOH solution as a reference. 36 Addition of Cu 2+ ions greatly quenches the fluorescence intensity of probe 5 , along with a slight redshift in the emission maximum. Upon addition of 1 equiv of Cu 2+ ions to the solution of probe 5 , the fluorescence intensity is quenched over 95% of its original intensity, along with a shift in the emission maximum from 536 to 545 nm.…”

“…As shown in Figure , free probe 5 has a strong emission band peaked at the wavelength of 536 nm with an excitation wavelength of 460 nm. The fluorescence quantum yield (Φ) of free probe 5 in aqueous solution is determined to be 10.5%, using the fluorescein in 0.1 N NaOH solution as a reference . Addition of Cu 2+ ions greatly quenches the fluorescence intensity of probe 5 , along with a slight redshift in the emission maximum.…”