Showing papers on "Xanthene published in 2019"

Guiding the Design of Organic Photocatalyst for PET-RAFT Polymerization: Halogenated Xanthene Dyes

Abstract: By examining structurally similar halogenated xanthene dyes, this study establishes a guiding principle for resolving structure-property- performance relationships in the photocontrolled PET-RAFT polymerization system (PET-RAFT: photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer). We investigated the effect of the halogen substituents on the photophysical and electrochemical properties of the xanthene dyes acting as photocatalysts and their resultant effect on the performance of PET-RAFT polymerization. Consideration of the structure- property-performance relationships allowed design of a new xanthene photocatalyst, where its photocatalytic activity (oxygen tolerance and polymerization rate) was successfully optimized for PET-RAFT polymerization. We expect that this study will serve as a theoretical framework in broadly guiding the design of high performance photocatalysts for organic photocatalysis.

A diversity-oriented rhodamine library for wide-spectrum bactericidal agents with low inducible resistance against resistant pathogens

Abstract: Antimicrobial resistance is a public health emergency and warrants coordinated global efforts. Challenge is that no alternative molecular platform has been identified for discovery of abundant antimicrobial hit compounds. Xanthene libraries have been screened for bioactive compounds. However, the potentially accessible chemistry space of xanthene dyes is limited by the existing xanthene synthesis. Herein we report a mild one-step synthesis, which permits late-stage introduction of a xanthene moiety onto i.e. natural products, pharmaceuticals, and bioactive compounds and construction of a focused library of rhodamine dyes exhibiting facile functional, topographical and stereochemical diversity. In vitro screening yields 37 analogs with mid-to-high bactericidal activity against WHO priority drug-resistant pathogens. These findings suggest that synthetic dye libraries exhibiting high structural diversity is a feasible chemical space combating antibacterial resistance, to complement the natural sources.

Green Synthesis of ZnO Nanoparticles via Sol-gel Method and Investigation of Its Application in Solvent-free Synthesis of 12-Aryl-tetrahydrobenzo[α]xanthene-11-one Derivatives Under Microwave Irradiation

Abstract: In this work, zinc oxide (ZnO) nanoparticles were fabricated using Arabic gum as a reducing and stabilizing agent by the novel sol-gel method without adding any surfactants. The synthesized nanoparticles were characterized by Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), and scanning electron microscopy (SEM). Subsequently, ZnO nanoparticles as efficient catalysts were consumed for the three-component coupling of 2-naphthol, aldehydes, and dimedone under microwave irradiation and solvent-free conditions in order to furnish the corresponding synthesis of 12-aryl-tetrahydrobenzo[α]xanthene-11-one derivatives in high yields.

Altering Fundamental Trends in the Emission of Xanthene Dyes

Abstract: Fluorescent small molecules enable researchers and clinicians to visualize biological events in living cells, tissues, and organs in real time. Herein, the focus is on the structure and properties of the relatively rare benzo[ a]xanthenes that exhibit enhanced steric and electronic interactions due to their annulated structures. Three types of fluorophores were synthesized: (i) pH- and solvent-dependent seminaphthorhodafluors, (ii) pH- and solvent-independent seminaphthorhodafluors, and (iii) pH-independent but solvent-sensitive seminaphthorhodamines. The probes exhibited promising far-red to near-infrared (NIR) emission, large Stoke shifts, broad full width at half-maximum (fwhm), relatively high quantum yields, and utility in immunofluorescence staining. Deviation of the π-system from planarity due to changes in the fluorophore ionization state resulted in fluorescence properties that are atypical of common xanthene dyes.

Four New Insecticidal Xanthene Derivatives from the Mangrove-Derived Fungus Penicillium sp. JY246.

Abstract: Four new xanthene derivatives, penicixanthenes A-D (1-4), and one known compound 5 were isolated from a marine mangrove endophytic fungus Penicillium sp. JY246 that was obtained from the stem of Ceriops tagal. Their structures were determined by detailed NMR, MS spectroscopic data, modified Mosher's method, and calculated electronic circular dichroism data. All of the isolated compounds were examined for insecticidal activity. Compounds 2 and 3 showed growth inhibition activity against newly hatched larvae of Helicoverpa armigera Hubner with the IC50 values 100 and 200 μg/mL, respectively, and compounds 1, 3, and 4 showed insecticidal activity against newly hatched larvae of Culex quinquefasciatus with LC50 values of 38.5 (±1.16), 11.6 (±0.58), and 20.5 (±1) μg/mL, respectively. The four xanthene derivatives have the potential to be developed as new biopesticides.

Immobilization of Lewis acidic ionic liquid on perlite nanoparticle surfaces as a highly efficient solid acid catalyst for the solvent-free synthesis of xanthene derivatives

Abstract: In this study, perlite nanoparticles were prepared through a simple method and then modified with Lewis acidic ionic liquid (perlite NP@IL/ZrCl4) through a two step procedure. The prepared solid acid catalyst was characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX) and thermo gravimetric analysis (TGA). Perlite NP@IL/ZrCl4 was used as a new solid acid, reusable and green heterogeneous nanocatalyst for the one-pot synthesis of xanthene derivatives. Synthesis of xanthenes was performed under solvent free conditions using a catalytic amount (0.005 g, 0.4 mol%) of the prepared catalyst with simple work-up and high to excellent yield of products. The reusability and high efficiency of this catalyst makes this method attractive for large scale environment-friendly operations.

Iridium-Promoted B-B Bond Activation: Preparation and X-ray Diffraction Analysis of a mer-Tris(boryl) Complex.

Abstract: The tris(boryl) complex Ir(Bcat)3{κ3-P,O,P-[xant(PiPr2)2]} [Bcat = catecholboryl; xant(PiPr2)2 = 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene] has been prepared and characterized by X-ray dif...

Organophotoredox Catalysis: Visible-light-induced Multicomponent Synthesis of Chromeno[4, 3-b]chromene and Hexahydro-1H-xanthene Derivatives

Abstract: In recent years, photoredox catalysis using eosin Y has gained considerable significance in organic chemistry. It is evolving as a powerful approach in modern organic synthesis for the activation of small molecules.The use of organic dyes to convert visible light into chemical energy by involving a single-electron transfer with organic substrates has innumerable applications.The present strategy is the first example of visible light promoted, aerobic, oxidative cyclization of chromeno[4,3-b]chromenes and hexahydro-1H-xanthenes via the formation of C–O and C–C bonds to afford excellent yield of the products in a simple one-pot operation under mild reaction conditions.The major advantages of the present methodology include short reaction time, cost effectiveness, easy work-up, broad substrate scope and high atom economy.

Graphene Oxide Incorporated Strontium Nanoparticles as a Highly Efficient and Green Acid Catalyst for One-Pot Synthesis of Tetramethyl-9-aryl-hexahydroxanthenes and 13-Aryl-5H-dibenzo[b,i]xanthene-5,7,12,14(13H)-tetraones Under Solvent-Free Conditions

Abstract: An efficient, inexpensive and recyclable graphene oxide/strontium nanocatalyst was synthesized and applied in a pseudo three-component, one-pot cyclocondensation of aromatic aldehydes and dimedone/lowson to afford the corresponding 3,3,6,6-tetramethyl-9-aryl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-diones and 13-aryl-5H-dibenzo[b,i]xanthene-5,7,12,14(13H)-tetraones in high yields under solvent-free conditions. To the best of our knowledge, there are no literature reports on applying graphene oxide/strontium as a nanocatalyst for xanthene derivatives synthesis. The key potential benefits of the present method are including high yields, short reaction time, easy workup, recyclability of catalyst and ability to tolerate a variety of functional groups which gives economical as well as ecological rewards. The nanocatalyst easily separated from the reaction mixture easily by applying an external magnet and reused at least six times without noticeable degradation in catalytic activity.

High acidity cellulose sulfuric acid from sulfur trioxide: a highly efficient catalyst for the one step synthesis of xanthene and dihydroquinazolinone derivatives

Abstract: A cellulose sulfonate catalyst (HS-cellulose sulfonate) with high stability, excellent catalytic activity and high acidity value (about 1.55 mmol g−1) was successfully prepared by SO3 gas phase sulfonation. The basic morphology and nanostructure of the catalyst were determined by HRTEM, XRD, IR, TG, etc. In addition, the catalyst was applied to the catalytic reaction of a dihydroquinazolinone derivative and a xanthene compound, and very valuable results were obtained. The development and preparation of cellulose sulfonate catalysts provide a good approach for the development and application of cellulose, and also an important application of green organic catalytic synthesis methodology.

Uncatalyzed Oxidative C-H Amination of 9,10-Dihydro-9-Heteroanthracenes: A Mechanistic Study.

Abstract: A new method for the one-step C-H amination of xanthene and thioxanthene with sulfonamides is reported, without the need for any metal catalyst. A benzoquinone was employed as a hydride (or two-electron and one-proton) acceptor. Moreover, a previously unknown and uncatalyzed reaction between iminoiodanes and xanthene, thioxanthene and dihydroacridines (9,10-dihydro-9-heteroanthracenes or dihydroheteroanthracenes) is disclosed. The reactions proceed through hydride transfer from the heteroarene substrate to the iminoiodane or benzoquinone, followed by conjugate addition of the sulfonamide to the oxidized heteroaromatic compounds. These findings may have important mechanistic implications for metal-catalyzed C-H amination processes involving nitrene transfer from iminoiodanes to dihydroheteroanthracenes. Due to the weak C-H bond, xanthene is an often-employed substrate in mechanistic studies of C-H amination reactions, which are generally proposed to proceed via metal-catalyzed nitrene insertion, especially for reactions involving nitrene or imido complexes that are less reactive (i.e., less strongly oxidizing). However, these substrates clearly undergo non-catalyzed (proton-coupled) redox coupling with amines, thus providing alternative pathways to the widely assumed metal-catalyzed pathways.

The optical properties of 9-amino-9H-xanthene derivatives in different pH and their application for biomarkers in lysosome and mitochondria

Abstract: Two xanthene compounds attached with 4-pyridinylimino (2a) and 2-quinolinylimino (2b) were prepared. Their deprotonated-protonated equilibrium between pyridine/quinoline/ xanthene units and the corresponding pyridinum/quinolinium/xanthylium units were evaluated in different pH by absorption and emission spectra. Probes 2a-b gave the colorimetric changes and emission responses at 550–750 nm, and their pKas (2a: pKa1 = 4.53, pKa2 = 5.95; 2b: pKa1 = 2.33, pKa2 = 6.18) were calculated by emission spectra. To verify the protonation process of probes 2a-b, the other two xanthylene derivatives attached with pyridinium (3a) and quinolinium (3b) were designed and synthesized; they exhibited only the equilibrium between xanthene and xanthylium as expected. Probe 3a showed a ratiometric change at 525–750 nm, and probe 3b displayed an OFF–ON emission at 500–700 nm with the decrease of the solution acidity. The calculated pKas were 6.18 and 1.49, respectively. Moreover, the fluorescent imaging experiments indicated that probes 2a–b were lysosome biomarkers while probes 3a–b were mitochondrial biomarkers for HeLa cells.

Acrotrione: An Oxidized Xanthene from the Roots of Acronychia pubescens.

Abstract: A new oxidized xanthene, acrotrione (1), and two known acetophenones (2 and 3) were isolated from a methanol extract of the roots of Acronychia pubescens. The structure of 1 was elucidated on the basis of its (+)-HRESIMS, 2D NMR, and ECD data. Acritrione (1) contains an unusual oxidized furo[2,3-c]xanthene moiety that has not been previously reported. Moderate antiplasmodial activity for these natural products against chloroquine-sensitive (3D7) and chloroquine-resistant (Dd2) Plasmodium falciparum was determined with IC50 values ranging from 1.7 to 4.7 μM.

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.