Showing papers on "Xanthene published in 2014"

Inhibitors of β-Site Amyloid Precursor Protein Cleaving Enzyme (BACE1): Identification of (S)-7-(2-Fluoropyridin-3-yl)-3-((3-methyloxetan-3-yl)ethynyl)-5′H-spiro[chromeno[2,3-b]pyridine-5,4′-oxazol]-2′-amine (AMG-8718)

Abstract: We have previously shown that the aminooxazoline xanthene scaffold can generate potent and orally efficacious BACE1 inhibitors although certain of these compounds exhibited potential hERG liabilities. In this article, we describe 4-aza substitution on the xanthene core as a means to increase BACE1 potency while reducing hERG binding affinity. Further optimization of the P3 and P2′ side chains resulted in the identification of 42 (AMG-8718), a compound with a balanced profile of BACE1 potency, hERG binding affinity, and Pgp recognition. This compound produced robust and sustained reductions of CSF and brain Aβ levels in a rat pharmacodynamic model and exhibited significantly reduced potential for QTc elongation in a cardiovascular safety model.

Chitosan synergistically enhanced by successive Fe3O4 and silver nanoparticles as a novel green catalyst in one-pot, three-component synthesis of tetrahydrobenzo[α]xanthene-11-ones

Abstract: Chitosan (CS) is modified with Fe 3 O 4 nanoparticles composite through in situ co-precipitation of Fe 3+ and Fe 2+ ions via NH 4 OH in an aqueous solution, resulting in magnetic Fe 3 O 4 /CS NPs. Adsorption of Ag + ions on the surface of the latter, followed by green reduction of Ag + via ascorbic acid, renders Fe 3 O 4 /CS-Ag NPs which shows an excellent catalytic activity toward one-pot, three-component synthesis of 12-aryl-8,9,10,12-tetrahydrobenzo[ α ]xanthene-11-one derivatives. The composition of the nanocatalyst is analyzed by FT-IR, XRD, TGA, VSM, ICP, SEM and TEM. Hence unique heterogeneous Fe 3 O 4 /CS-Ag NPs acts as an excellent green catalyst giving high yield product with good recyclability and without significant loss of the activity.

Interaction of eosin and its ester derivatives with aqueous biomimetic micelles: Evaluation of photodynamic potentialities

Abstract: In this paper, the physicochemical and photophysical properties of xanthene dyes interacting with micelles were evaluated. Xanthenes are potential photosensitizers for photodynamic therapy. The dyes were eosin Y and its ester derivatives with methyl, butyl and decyl alkyl groups. In aqueous media at physiological pH eosin is present as dianionic protolytic form while its esters are monoanionic. Analysis of the water/octanol partition coefficient showed that the eosin is the most hydrophilic compound and the hydrophobicity increases as the alkyl chain of the ester increases: eosin

Synthesis of dibenzoxanthene and acridine derivatives catalyzed by 1,3-disulfonic acid imidazolium carboxylate ionic liquids

Abstract: New members of 1,3-disulfonic acid imidazolium carboxylate ionic liquids [DSIM][X] (where X = [CH3COO]−, [CCl3COO]−, [CF3COO]−) were prepared and characterized by 1H NMR,13C NMR, FT-IR, TGA,UV-vis and elemental analysis. The more acidic ILs [DISM][CCl3COO] and [DSIM][CF3COO] were efficiently utilized as recyclable catalysts for the preparation of 14H-dibenzo[a,j]xanthene and 1,8-dioxo-decahydroacridine derivatives in short times under solvent-free conditions at 80–100 °C with excellent yields. The above two ILs could be effectively utilized as catalysts for the synthesis of 1,8-dioxo-decahydroacridine in water at the same temperature.

Rapid one pot synthesis of xanthene derivatives by an efficient and reusable nano-ZnAl2O4 – An insight into a new process

Abstract: Nano-ZnAl 2 O 4 was synthesized by blending metal-citrate complex-acrylamide polymer using the precursor method. Powder X-ray diffraction analysis of the catalyst affirmed that the spinel oxide was phase pure. Elemental analysis was confirmed by Energy Dispersive X-ray analysis. Transmission Electron Microscopic (TEM) analysis and Scherrer's formula revealed that the particles were found to be in the order of 20 nm in size. Thermal stability of the catalyst was analyzed by thermogravimetric and differential thermal analysis (TG-DTA). Total acidity of the nano-ZnAl 2 O 4 evaluated by NH 3 -TPD was 8.8 mmol NH 3 /g. Diversity in the synthesis of xanthene derivatives was investigated using nanozinc aluminate as a catalyst. Nanoform of the catalyst showed better activity than the bulk form due to its large surface area 50 m 2 /g. The 2,2′-arylmethylene bis (3-hydroxy-2-cyclohexene-1-one), 2,2′-arylmethylene bis (3-hydroxy-5,5-dimethyl-2-cyclohexene-1-one) and 1-Oxo-hexahydroxanthenes were synthesized rapidly using ZnAl 2 O 4 and the catalyst was successfully recycled without any loss of activity.

Non-radiative decay paths in rhodamines: new theoretical insights.

Abstract: We individuate a photoinduced electron transfer (PeT) as a quenching mechanism affecting rhodamine B photophysics in solvent. The PeT involves an electron transfer from the carboxylate group to the xanthene ring of rhodamine B. This is finely modulated by the subtle balance of coulombic and non-classical interactions between the carboxyphenyl and xanthene rings, also mediated by the solvent. We propose the use of an electronic density based index, the so called DCT index, as a new tool to assess and quantify the nature of the excited states involved in non-radiative decays near the region of their intersection. In the present case, this analysis allows us to gain insight on the interconversion process from the bright state to the dark state responsible for the quenching of rhodamine B fluorescence. Our findings encourage the use of density based indices to study the processes affecting excited state reactions that are characterized by a drastic change in the excitation nature, in order to rationalize the photophysical behavior of complex molecular systems.

Introduction of a new bi-SO3H ionic liquid based on 2,2′-bipyridine as a novel catalyst for the synthesis of various xanthene derivatives

Abstract: In this study, 1,1′-disulfo-[2,2′-bipyridine]-1,1′-diium chloride, [BiPy](SO3H)2Cl2 as a new ionic liquid, is prepared, characterized and used as an efficient catalyst for the promotion of the synthesis of various symmetric and asymmetric xanthene derivatives under solvent free conditions. All products were formed in excellent yields over short reaction times. Easy preparation of the catalyst, simple and easy work-up, mild reaction conditions, low cost, excellent yields and short reaction times are some of the advantages of this work.

Bio-inspired benzo[k,l]xanthene lignans: synthesis, DNA-interaction and antiproliferative properties

Abstract: In this work twelve benzo[k,l]xanthene lignans were synthesized by biomimetic, Mn-mediated oxidative coupling of caffeic esters and amides. These compounds, bearing different flexible pendants at position C1/C2 of the aromatic core, interact with DNA in a dual mode, as confirmed by DF-STD NMR analysis and molecular docking: the planar core acts as a base pair intercalant, whereas the flexible pendants act as minor groove binders. Their antiproliferative activity was evaluated on a panel of six tumor cell lines: HT-29, Caco-2, HCT-116 (human colon carcinoma), H226, A549 (human lung carcinoma), and SH-SY5Y (human neuroblastoma). All compounds under study, except 29, resulted in activity against one or more cell lines, and the markedly lipophilic esters 13 and 28 showed the highest activity. Compound 13 was more active than the anticancer drug 5-fluorouracil (5-FU) towards HCT-116 (colon, GI50 = 3.16 μM) and H226 (lung, GI50 = 4.33 μM) cell lines.

Lead Optimization and Modulation of hERG Activity in a Series of Aminooxazoline Xanthene β-Site Amyloid Precursor Protein Cleaving Enzyme (BACE1) Inhibitors

Abstract: The optimization of a series of aminooxazoline xanthene inhibitors of β-site amyloid precursor protein cleaving enzyme 1 (BACE1) is described. An early lead compound showed robust Aβ lowering activity in a rat pharmacodynamic model, but advancement was precluded by a low therapeutic window to QTc prolongation in cardiovascular models consistent with in vitro activity on the hERG ion channel. While the introduction of polar groups was effective in reducing hERG binding affinity, this came at the expense of higher than desired Pgp-mediated efflux. A balance of low Pgp efflux and hERG activity was achieved by lowering the polar surface area of the P3 substituent while retaining polarity in the P2′ side chain. The introduction of a fluorine in position 4 of the xanthene ring improved BACE1 potency (5–10-fold). The combination of these optimized fragments resulted in identification of compound 40, which showed robust Aβ reduction in a rat pharmacodynamic model (78% Aβ reduction in CSF at 10 mg/kg po) and also ...

Oxidation of alcohols and activated alkanes with Lewis acid-activated TEMPO.

Abstract: The reactivity of MCl3(η1-TEMPO) (M = Fe, 1; Al, 2; TEMPO = 2,2,6,6-tetramethylpiperidine-N-oxyl) with a variety of alcohols, including 3,4-dimethoxybenzyl alcohol, 1-phenyl-2-phenoxyethanol, and 1,2-diphenyl-2-methoxyethanol, was investigated using NMR spectroscopy and mass spectrometry. Complex 1 was effective in cleanly converting these substrates to the corresponding aldehyde or ketone. Complex 2 was also able to oxidize these substrates; however, in a few instances the products of overoxidation were also observed. Oxidation of activated alkanes, such as xanthene, by 1 or 2 suggests that the reactions proceed via an initial 1-electron concerted proton–electron transfer (CPET) event. Finally, reaction of TEMPO with FeBr3 in Et2O results in the formation of a mixture of FeBr3(η1-TEMPOH) (23) and [FeBr2(η1-TEMPOH)]2(μ-O) (24), via oxidation of the solvent, Et2O.

Nitrogen-doped metal-free carbon catalysts for aerobic oxidation of xanthene

Abstract: N-doped carbons were prepared from a commercial activated carbon (AC) by heat treatments in pure NH 3 , an NH 3 –air mixture, and NO and these were used for a model reaction of aerobic oxidation of xanthene to xanthone (XO). The catalytic activity of AC for the title reaction was greatly enhanced by N-doping and the enhancement in the activity depended on the N source gasses used. The effectiveness of the three gases for both N-doping and enhancing the activity was in an order of NH 3 –air > NH 3 > NO. The temperature of N-doping also affected the catalyst activity but not so significantly. X-ray photoelectron spectroscopy (XPS) indicated the presence of pyridine-type and pyrrole-/pyridone-type N species. The catalytic activity of N-doped carbon was correlated with the ratio of the amount of pyridine-type N against that of ether-type O species. The structures of the active sites were discussed on the basis of the XPS and reaction results. Metal-free N-doped AC was less active than a commercial Ru/AC catalyst but more active than a commercial Pd/AC one. The activity of N-carbon slightly decreased after the first recycling but it remained almost the same during the following two-time recycling.

Synthesis and characterization of phosphate anchored MnO2 catalyzed solvent free synthesis of xanthene laser dyes

Abstract: A highly stable and environmentally benign phosphate anchored MnO2 (P-MnO2) catalyst has been prepared. The catalyst has been characterized by using TGA, FTIR, Raman, XRD, UV-DRS, XPS, FESEM, and EDAX techniques. The catalytic behavior of P-MnO2 has been demonstrated for the synthesis of 1,8-dioxooctahydroxanthene and 14-aryl (alkyl)-14H-dibenzo[a,j]xanthene laser dye derivatives under solvent free conditions. Recyclability, high yield, short reaction time, relative non-toxicity and easy workup are the advantages of the presented catalyst.

A Novel Ratiometric Fluorescent Mercury Probe Based on Deprotonation-ICT Mechanism

Abstract: A new NBD-rhodamine dye (1) was developed as a colorimetric and ratiometric fluorescent chemosensor for Hg2+ with good selectivity in aqueous ethanol solutions under neutral to basic conditions. Sensor 1 showed absorption at 468 nm and a weak emission at 529 nm (ϕ F = 0.063) in ethanol/aqueous tris buffer (9:1, v/v) of pH 9.17 solution. Bathochromic shifts in both absorption (492 nm) and fluorescence spectra (569 nm, ϕ F = 0.129), respectively upon addition of 2 equiv. of Hg2+ were observed. The ring-opening reaction of the spirolactam form to the corresponding xanthene form was not found. The interaction of Hg2+ with chemosensor 1 resulted in the deprotonation of the secondary amine conjugated to the NBD component so that the electron-donating ability of the N atom was enhanced. Deprotonation-ICT mechanism of secondary amines was suggested for the ratiometric fluorescent chemosensing for Hg2+.

pH-responsive switchable aggregation phenomena of xanthene dyes adsorbed on tungsten(VI) oxide colloid surface

Abstract: The surface interactions between xanthene (XN) dyes, including rhodamine B, rhodamine 3B, rhodamine 19, rhodamine 6G, rhodamine 110, and rhodamine 123, and tungsten(VI) oxide (WO3) colloid particles were investigated. These XN dyes were strongly adsorbed as a monolayer onto the WO3 surface via the electrostatic interaction between their peripheral cationic amino substituents and negatively surface-charged WO3 colloid particles, and most of the ones adsorbed eventually formed stable π-stacked dimers. The geometry of dimers formed on the WO3 colloid surface is discussed on the basis of the molecular exciton theory framework. Cationic XN dyes formed the approximately ideal face-to-face H-dimers on the WO3 colloid surface, whereas zwitterionic ones had a higher tendency to form the oblique J-dimers. Additionally, we have experimentally demonstrated the possibility of pH-induced switching between H- and J-aggregation modes of the XN dye’s dimers formed on the WO3 colloid surface. The findings lead to a better ...

An efficient ratiometric fluorescent excimer probe for hypochlorite based on a cofacial xanthene-bridged bispyrene

Abstract: In this paper, by employing a rigid xanthene scaffold as a bridge, we for the first time report a cofacial bispyrene derivative DPH as an efficient ratiometric fluorescent excimer probe for hypochlorite (OCl−). The probe is comprised of a rigid xanthene scaffold and two parallel pyrenes, which are linked by an OCl−-sensitive dicarboxylic acid hydrazide group. The introduction of OCl−, however, will induce oxidation of the dicarboxylic acid hydrazide moiety into a diimide group, and the subsequent hydrolysis of the diimide, to give 1-pyrenecarboxylic acid which exhibits a monomer emission at about 380 nm, with its intensity increasing with the addition of increased concentration of OCl−. Meanwhile, the excimer emission intensity gradually decreases. Such a ratiometric fluorescent response of the probe affords a high sensitivity to OCl−, with a linear response concentration range of 1 to 300 μM, and a detection limit of 0.35 μM for OCl−. It also shows a high selectivity for OCl− with no interference observed from other common anions and small molecules. Moreover, it can also act as a colorimetric probe for OCl− due to the cyan-to-blue fluorescence color change. It has been preliminarily used for practical detection of OCl− in river water samples with satisfying results.

Synthesis, characterization and magnetic properties of novel heat resistant polyimide nanocomposites derived from 14H-dibenzo [a,j] xanthene

Abstract: New magnetic and heat resistant polyimide (PI) nanocomposites containing two different types of magnetic nanoparticles were successfully prepared by a solution intercalation technique. New PI derived from 14H-dibenzo [a,j] xanthene, which contain benzophenone, amide and ether moieties, was synthesized by thermal cyclization of an aromatic precursor polymer, obtained from the reaction of the new diamine N-(4-(4-(14H-dibenzo [a,j] xanthen-14-yl) phenoxy) phenyl)-3,5-diaminobenzamide and 3,3’,4,4’-benzophenone tetracarboxylic dianhydride (BTDA). The synthesized PI was characterized by Fourier-transform infrared (FTIR), nuclear magnetic resonance (1H NMR), UV-vis and photoluminescence (PL) spectroscopy. The structural and electronic properties of the xanthene-based polyimide unit were studied by ab intio DFT method using the B3LYP/6-31G (d) level of theory. The HOMO, LUMO and band gap (ΔE = ELUMO - EHOMO) energies of the polyimide unit were calculated. PI nanocomposites were prepared by coating magnetite (Fe3O4) nanoparticles sequentially with silica (SiO2) and 1-methyl-3-(triethoxysilylpropyl) imidazolium chloride; the Fe3O4 and surface-modified Fe3O4 (Fe3O4@SiO2-ImCl) nanoparticles were then dispersed in the poly (amic acid) solutions and thermally imidized to form PI/Fe3O4 and PI/Fe3O4@SiO2-ImCl nanocomposites. The morphology, crystalline phase, thermal stability and magnetization properties of the resultant materials were characterized by field emission scanning electron microscopy (FE-SEM) transmission electron microscope (TEM), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), vibrating sample magnetometer (VSM) and FTIR techniques. The results indicated that the as-prepared nanocomposites exhibited superparamagnetic properties and improvements in the thermal stability compared to neat polyimide. Furthermore, the Fe3O4@SiO2-ImCl nanoparticles has better dispersion in the polymer matrix, than the uncoated Fe3O4 nanoparticles, and thus the PI/Fe3O4@SiO2-ImCl nanocomposite prepared using the coated nanoparticles exhibits a better intercalated morphology and improved thermal properties than the PI/Fe3O4 nanocomposite.

Asymmetrical si rhodamine and rhodol synthesis

Abstract: [Problem] To provide: a compound resulting from substituting with a silicon atom the oxygen atom at position 10 of a xanthene ring site of a rhodamine of which amino groups at position 3 and position 6 have an asymmetrical structure; a method for producing the compound; and a fluorescent probe that uses the compound. [Solution] The compound represented by general formula (I) or a salt thereof.

Kinetic and mechanistic studies of carbon-to-metal hydrogen atom transfer involving Os-centered radicals: evidence for tunneling.

Abstract: We have investigated the kinetics of novel carbon-to-metal hydrogen atom transfer reactions, in which homolytic cleavage of a C–H bond is accomplished by a single metal-centered radical. Time-resolved IR spectroscopic measurements revealed efficient hydrogen atom transfer from xanthene, 9,10-dihydroanthracene, and 1,4-cyclohexadiene to Cp(CO)2Os• and (η5-iPr4C5H)(CO)2Os• radicals, formed by photoinduced homolysis of the corresponding osmium dimers. The rate constants for hydrogen abstraction from these hydrocarbons are in the range 1.5 × 105 M–1 s–1 to 1.7 × 107 M–1 s–1 at 25 °C. For the first time, kinetic isotope effects for carbon-to-metal hydrogen atom transfer were determined. Large primary deuterium kinetic isotope effects of 13.4 ± 1.0 and 16.8 ± 1.4 were observed for the hydrogen abstraction from xanthene to form Cp(CO)2OsH and (η5-iPr4C5H)(CO)2OsH, respectively, at 25 °C. Temperature-dependent measurements of the kinetic isotope effects over a 60 °C temperature range were carried out to obtain th...

Introduction of O-sulfonated poly(4-vinylpyrrolidonium) chloride as a polymeric and reusable catalyst for the synthesis of xanthene derivatives

Abstract: O-Sulfonated poly(4-vinylpyrrolidonium) chloride is prepared from the reaction of poly(4-vinylpyrrolidone) [PVP], as a cheap and commercially available reagent, and neat chlorosulfonic acid at room temperature. A variety of techniques including infrared spectra (IR), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD), pH analysis and Hammett acidity (Ho) were used to characterize this solid acid. This polymeric reagent showed excellent catalytic activity for the synthesis of xanthene derivatives including 1,8-dioxooctahydroxanthenes, 14-aryl-14H-dibenzo[a,j] xanthenes and 12-aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-ones under solvent free conditions. The products were formed in excellent yields over short reaction times and the catalyst can be reused several times without any appreciable loss in its activity.

Efficient one-pot synthesis of 14-aryl-14H-dibenzo[a,j]xanthene derivatives promoted by niobium pentachloride

Abstract: A simple and efficient procedure for the synthesis of 14-aryl-14H-dibenzo[a,j ]xanthene derivatives through one-pot condensation of 2-naphthol with aryl aldehydes in the presence of niobium pentachloride is described. The reactions were carried out using 25 mole % of NbCl5 ,a t ambient temperature, and in acceptable reaction times, affording excellent yields of the products. c 2014 Institute of Chemistry, Slovak Academy of Sciences

Chemistry and Photochemistry of 2,6-Bis(2-hydroxybenzilidene)cyclohexanone. An Example of a Compound Following the Anthocyanins Network of Chemical Reactions

Abstract: The kinetics and thermodynamics of the 2,6-bis(2-hydroxybenzilidene)cyclohexanone chemical reactions network was studied at different pH values using NMR, UV–vis, continuous irradiation, and flash photolysis. The chemical behavior of the system partially resembles anthocyanins and their analogue compounds. 2,6-Bis(2-hydroxybenzilidene)cyclohexanone exhibits a slow color change from yellow to red styrylflavylium under extreme acidic conditions. The rate constant for this process (5 × 10–5 s–1) is pH independent and controlled by the cis–trans isomerization barrier. However, the interesting feature is the appearance of the colorless compound, 7,8-dihydro-6H-chromeno[3,2-d]xanthene, isolated from solutions of acid to neutral range, characterized by 1H NMR and single crystal X-ray diffraction. Light absorption by 2,6-bis(2-hydroxybenzilidene)cyclohexanone solutions immediately after preparation exclusively results in cis-isomer as photoproduct, which via hemiketal formation yields (i) red styrylflavylium by d...

A New Access to 1,8-Dioxooctahydroxanthenes Using Yttrium(III) Nitrate Hexahydrate and Tin(II) Chloride Dihydrate as Effective and Reusable Catalysts

Abstract: An efficient and environmentally adapted synthesis of xanthene derivatives by condensation of a wide range of aryl aldehydes and cyclohexane-1,3-diones in the presence of catalytic amounts of yttrium(III) nitrate hexahydrate and tin(II) chloride dihydrate is demonstrated.