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Different Substituents (different + substituent)
Selected AbstractsThree-Component Synthesis of Highly Functionalized 5-AcetyloxazolesCHEMISTRY - A EUROPEAN JOURNAL, Issue 22 2009Tilman Lechel Abstract By a flexible three-component synthesis, alkoxy-substituted enamides are easily available from lithiated alkoxyallenes, nitriles and carboxylic acids (see scheme). The treatment of these versatile intermediates with trifluoroacetic acid provided 5-acetyloxazoles in moderate to good yields. Different substituents are possible at C-2 and C-5 and the 5-acetyl group is a suitable handle for further synthetic transformations. [source] Substituent Effects on Crosslike Packing of 2,,7,-Diaryl- spiro(cyclopropane-1,9,-fluorene) Derivatives: Synthesis and Crystallographic, Optical, and Thermal Properties,ADVANCED FUNCTIONAL MATERIALS, Issue 2 2007Z. Wang Abstract A series of 2,,7,-diarylspiro(cyclopropane-1,9,-fluorene) derivatives are efficiently synthesized and characterized to determine the reason for the "green-light" emission of these compounds. These compounds exhibit bright-violet to blue photoluminescence (PL) (,PLmax,=,353,419,nm) with excellent PL quantum efficiencies (,PL,=,83,100,%) in solution and show high thermal stabilities (Td,=,267,474,°C). The variation of the optical properties of these molecules in the solid state depends on the different stacking modes of these compounds containing different substituents, which are revealed by crystallographic analysis. CH,, hydrogen bonds instead of intermolecular ,,, interactions act as the driving force between adjacent fluorenes, even though a very small dialkyl group (cyclopropane) is introduced at the C-9 position of fluorene. The crosslike molecular stacking efficiently reduces the energy transfer between the herring-like aggregates and therefore results in the absence of a "green-light" emission tail. In order to determine the cause of the "green-light" emission tails, the fluorescence spectra of the films annealed in N2 or in air are recorded. Broad green-light emission tails were observed for the films annealed in air, which might be caused by fluorenone defects generated during processing or during the course of the photophysical analysis by reaction with residual oxygen. [source] Zinc-Catalyzed Domino Hydroamination,Alkyne AdditionADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Mustafa Biyikal Abstract The first zinc-catalyzed one-step synthesis of quaternary propargylamines with four different substituents is described. The domino hydroamination,alkyne addition reaction gives access to functionalized propargylamines under mild conditions. [source] One-Pot Synthesis of Quinoline Derivatives Directly from Terminal Alkynes via Sequential Ruthenium(II) and Acid CatalysisADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Min Zhang Abstract A convenient one-pot synthesis of 2,3-disubstituted, 2,3,6-trisubstituted, and 2,3,6,7-tetrasubstituted quinoline analogues from terminal alkynes via sequential ruthenium(II) and para -toluenesulfonic acid (p -TSA) co-catalyzed reactions is described. The catalytic process is shown to take place first via intermediate formation of an allyl ketone and then addition of an aniline derivative to the allyl ketone. The p -TSA is a catalyst for both allyl ketone and quinoline synthetic steps. The method allowed us to synthesize a wide range of quinoline derivatives and introduce different substituents by employing various simple starting materials. The reaction allows the synthesis of halogen-containing products. [source] Chiral Phosphoric Acid-Catalyzed Enantioselective Aza-Friedel,Crafts Reaction of IndolesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2007Masahiro Terada Abstract A highly enantioselective 1,2-aza-Friedel,Crafts reaction of N - tert -butyldimethylsilylindole with N - tert -butoxycarbonyl aromatic imines is demonstrated using a BINOL-derived monophosphoric acid catalyst. The present approach provides efficient access to 3-indolylmethaneamines with aryl substituents in excellent enantioselectivities (up to 98,% ee). An inversion in the sense of enantioselection was found between monophosphoric acid catalysts bearing different substituents introduced at the 3,3,-position of binaphthyl backbone. We also calculated the three-dimensional structure of the monophosphoric acid catalysts to speculate on the inversion of the stereochemical outcome. [source] 1,3-Dipolar cycloaddition reaction of 4,5-dihydro-1H -imidazole 3-oxides with alkynesJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 2 2006Sergey A. Popov 4,5-Dihydro-1H -imidazole 3-oxides bearing different substituents at positions 1 and 2 of the heterocycle were shown to react with a wide range of acceptor-substituted alkynes forming corrsponding cycloadducts - derivatives of 1,2,3,7a-tetrahydroimidazo[1,2- b]isoxazole. High regioselectivity of this process stipulated by conjugation of the nitrogen atom with the nitrone group was revealed. [source] Recent cancer drug development with xanthone structuresJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 6 2009Younghwa Na Abstract Objectives Xanthones are simple three-membered ring compounds that are mainly found as secondary metabolites in higher plants and microorganisms. Xanthones have very diverse biological profiles, including antihypertensive, antioxidative, antithrombotic and anticancer activity, depending on their diverse structures, which are modified by substituents on the ring system. Although several reviews have already been published on xanthone compounds, few of them have focused on the anticancer activity of xanthone derivatives. In this review we briefly summarize natural and synthetic xanthone compounds which have potential as anticancer drugs. Key findings The interesting structural scaffold and pharmacological importance of xanthone derivatives have led many scientists to isolate or synthesize these compounds as novel drug candidates. In the past, extensive research has been conducted to obtain xanthone derivatives from natural resources as well as through synthetic chemistry. Xanthones interact with various pharmacological targets based on the different substituents on the core ring. The anticancer activities of xanthones are also dramatically altered by the ring substituents and their positions. Summary The biological activities of synthetic xanthone derivatives depend on the various substituents and their position. Study of the biological mechanism of action of xanthone analogues, however, has not been conducted extensively compared to the diversity of xanthone compounds. Elucidation of the exact biological target of xanthone compounds will provide better opportunities for these compounds to be developed as potent anticancer drugs. At the same time, modification of natural xanthone derivatives aimed at specific targets is capable of expanding the biological spectrum of xanthone compounds. [source] Comparative study of electronic structure and optical properties of a series of Pt(II) complexes containing different electron-donating and -withdrawing groups: a DFT studyJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 3 2010Xiao-Na Li Abstract We report a quantum-chemistry study of electronic structures and spectral properties of a series of Pt(II) complexes containing different substituents (CH3 (1), OCH3 (2), NO2 (3), CF3 (4), and COOH (5)). 1 and 2 have been previously synthesized in experiment, while 3,5 are artificial complexes that we suggest can be used to investigate the electron-withdrawing effect on charge injection, transport, absorption, and phosphorescence properties. The results reveal that the stronger electron-donating and -withdrawing groups show stronger absorption intensity, while the phosphorescence efficiency is generally higher for complexes containing electron-donating substituents. 1 and 2 are easier for hole injection, while 3,5 are easier for electron injection. The enhanced electron injection abilities of 3,5 will confine more excitons in the light-emitting layer (EML) and may not result in lower electroluminescence (EL) efficiency than 1 and 2. These results suggest that the three artificial complexes may be new emitters in organic light-emitting diodes (OLEDs). Copyright © 2009 John Wiley & Sons, Ltd. [source] Analysis of interaction modes in calix[4]arene,levofloxacin complexes by quantum methodsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 3 2006Alexandrine Lambert Abstract Host,guest interactions between chiral calix[4]arenes and the antibiotic levofloxacin are analyzed on the basis of quantum mechanical calculations at the density functional (for model systems) and semi-empirical levels. The calix[4]arene macrocycle carries two (+)-isomenthyl groups attached to opposing phenyl groups at the lower rim and different substituents (R,=,H, CH3, tBu, CH2CHCH2, COCH3 and NO2) are considered at the upper rim. Nitro derivatives are expected to form ionized complexes whereas the other derivatives should form neutral complexes with a very low stability. Copyright © 2006 John Wiley & Sons, Ltd. [source] Phenol radical cations and phenoxyl radicals in electron transfer from the natural phenols sesamol, curcumin and trolox to the parent radical cations of 1-chlorobutaneJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 8 2004R. Joshi Abstract The free electron transfer from sesamol, curcumin and trolox to solvent (1-chlorobutane) radical cations was studied. The solutes (ArOH) react with BuCl,+ at diffusion-controlled rates (,1010,dm3,mol,1,s,1) resulting, simultaneously, in phenol-type radical cations (ArOH,+) and phenoxyl radicals (ArO,) with an ArOH,+/ArO, ratio ,>,1;1. It was found that the kinetics are markedly affected by the different substituents on the aromatic ring of ArOH,+. The various ArOH,+ react with triethylamine with rate constants of ,109,dm3,mol,1,s,1, whereas ethanol and dioxane are ineffective as cation scavengers. The effect of substituents on the electron transfer and the ArOH,+/ArO, ratio is discussed on the basis of experimental data and quantum chemical calculations. Copyright © 2004 John Wiley & Sons, Ltd. [source] Substituent effects on benzyne electronic structuresJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 9 2001William T. G. Johnson Abstract The effect of inductive strength and ,-conjugating tendency on the structure and energetics of singly substituted benzynes is studied for different substituents. For amino and cyano substituents, all possible isomers are examined. For silyl and ammonio substituents, meta isomers are examined. Copyright © 2001 John Wiley & Sons, Ltd. [source] Alkyl side chain driven tunable red,yellow,green emission: Investigation on the new ,-conjugated polymers comprising of 2,7-carbazole unit and 2,1,3-benzo-thiadiazole units with different side chainsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2008Junping Du Abstract Four new soluble polymers containing a 2,7-carbazole unit and a 2,1,3-benzothiadiazole unit in the main chain were synthesized by Suzuki polycondensation. Variation of the substituent groups (R) at 5-position of 2,1,3-benzothiadiazole unit resulted in different color emission of the copolymers. Thus, when R was CH3 (or H), the polymer showed yellow,green (or red) emission; whereas the polymers showed the emission from green to yellow,green, when R was CH2(CH2)5CH3 or CH2OCH(CH3)2. To investigate the nature of the color change, a Gaussian 03 program was used for estimation of the dihedral angles between a 5-R-2,1,3-benzothiadiazole unit and a 2,7-carbazole unit. The results showed that the different substituents at 5-position of 2,1,3-benzothiadiazole brought about different the dihedral angles, which gave the different conjugation levels to the polymers. Hence, the tunablity of emission color may be attributed to the different conjugation levels between 2,7-carbazole units and 5-R-2,1,3-benzothiadiazole units induced by simply changing substituent groups at 5-position of benzothiadiazole unit. Electrochemically, the copolymers exhibited a higher oxidation potential as well as the reversible reduction behavior bearing from 2,1,3-benzothiadiazole unit. To investigate the electroluminescent properties of the polymers, the nonoptimized devices were fabricated and the results showed that the electroluminescent emission wavelength was basically similar to that of the photoluminescent. All polymers showed good thermal stability with 5 wt % loss temperature of more than 296 °C. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1376,1387, 2008 [source] Synthesis and properties of novel conjugated poly(silylacetylene silazane)sJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2004Ji Dong Hu Abstract A series of novel conjugated polymers, poly(silylacetylene silazane)s having different substituents, were prepared by ammonolysis of the corresponding ,,,-dichlorosilyleneacetylene oligomers. The structures and properties of the poly(silylacetylene silazane)s were characterized by Fourier transform infrared, 1H, 13C, 29Si NMR, and elemental analyses, gel permeation chromatography, thermogravimetric analysis, differential scanning calorimetry, and spectrofluorophotometry. The resulting polymers had good thermal properties and were moderately fluorescent. Their thermal stability was improved, and obvious red shift was observed when a phenyl substituent was attached on a silicon atom of polymers in the emission spectra. These polymers have the potential to be used as light-emitting materials with good thermal stability. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2897,2903, 2004 [source] Phenothiazine photosensitizers for onium salt photoinitiated cationic polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2001Zaza Gomurashvili Abstract Phenothiazine compounds bearing a wide range of different substituents are excellent photosensitizers for onium salt cationic photoinitiators. These photosensitizers are generally operative in the mid- and long-range regions of the UV spectrum and are especially useful for enhancing the rate of photoinitiated cationic polymerization carried out utilizing both filtered and broadband UV emission sources. In this article, the syntheses of several different substituted phenothiazines are described and the ability of these compounds to photosensitize the photolysis of different onium salt photoinitiators is evaluated. Attempts were made to correlate the structure and spectral characteristics of the phenothiazines with their efficiency of photosensitization in the cationic photopolymerizations of several typical epoxide and vinyl ether monomers. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1187,1197, 2001 [source] Fragmentation pathways of acylated flavonoid diglucuronides from leaves of Medicago truncatulaPHYTOCHEMICAL ANALYSIS, Issue 3 2010ukasz Marczak Abstract Introduction , Flavonoids are important plant compounds occurring in tissues mostly in the form of glycoconjugates. Most frequently the sugar moiety is comprised of mono- or oligosaccharides consisting of common sugars like glucose, rhamnose or galactose. In some plant species the glycosidic moiety contains glucuronic acid and may be acylated by phenylpropenoic acids. Methodology , Flavonoid glyconjugates were extracted from leaves of Medicago truncatula ecotype R108 and submitted to analysis using high-performance liquid chromatography combined with high-resolution tandem (quadrupole-time of flight, QToF) mass spectrometry. Results , The studied leaf extracts contained 26 different flavonoid glycosides among which 22 compounds were flavone (apigenin, luteolin, chrysoeriol and tricin) glucuronides and 13 were acylated with aromatic acids (p -coumaric, ferulic or sinapic). The fragmentation pathways observed in positive and negative ion mass spectra differed substantially between each other and from these of flavonoid glycosides which did not contain acidic sugars. The application of high-resolution MS techniques allowed unequivocal differentiation between ions with the same nominal m/z values containing different substituents (e.g. ferulic acid or glucuronic acid). Eleven of the identified flavonoids have not been reported previously in this species. Perspectives , The presented unique fragmentation pathways of flavonoid glucuronates enable detection of these compounds in tissue extracts from different plant species. Copyright © 2009 John Wiley & Sons, Ltd. [source] Study of fragmentation pathways of lithiated ,,, -unsaturated thioesters by electrospray ionization mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 4 2010Cheng Guo The fragmentation pathways of lithiated ,,, -unsaturated thioesters with different substituents were investigated by electrospray ionization tandem mass spectrometry (ESI-MS/MS) in positive ion mode. In mass spectrometry of the ,,, -unsaturated thioesters, Ar-CHCH-CO-S-Ph, loss of PhSLi and elimination of a thiophenol were the two major fragmentation reactions of the lithiated molecules. The elemental compositions of all the ions were confirmed by high-resolution Fourier transform ion cyclotron resonance tandem mass spectrometry (FTICR-MS/MS). The thioesters studied here were para -monosubstituted on the phenyl ring of cinnamoyl and the electron-withdrawing groups favored loss of a thiophenol, whereas the electron-releasing groups strongly favored the competing reaction leading to the loss of PhSLi to form a cinnamoyl cation, Ar-CHCHCO+. The intensity ratios of the two competitive product ions were well correlated with the , substituent constants. The mechanisms of these two competing routes were further investigated by density functional theory (DFT) calculations. Copyright © 2010 John Wiley & Sons, Ltd. [source] A comparison of the electron ionization and electrospray behaviour of some N,N,-disubstituted hexahydropyrimidinesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 5 2006Liliana R. Orelli The behaviour of some N,N,-disubstituted hexahydropyrimidines, a class of naturally occurring compounds of biological and biomedical interest, has been studied in both electron ionization (EI) and electrospray ionization (ESI) modes coupled with collisional experiments (ESI-MSn). In both techniques, the [M,H]+ ions are highly abundant, even if their formation is generated by two different mechanisms, i.e. H. loss from the M+. species in the case of EI and hydride (H,) abstraction from the molecules in the case of ESI. Furthermore, due to the low, step-by-step internal energy deposition typical of collisional experiments performed in an ion trap mass spectrometer, different fragment ions were observed in EI and ESI-MSn collisions. In both cases, the ions can be related to the original structure and allow us to identify the positions in which the different substituents are present. Copyright © 2006 John Wiley & Sons, Ltd. [source] Evidence for an aryl migration during the electron impact induced fragmentation of substituted aryloxymethylquinoxalinesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 3 2002I. Starke The electron impact (EI) mass spectra of 34 differently substituted 2-phenoxymethyl-, 2-naphthyloxymethyl-, 2-pyridinyloxymethyl- and 2-chinolinyloxymethylquinoxalines were recorded. The fragmentation patterns were examined by metastable ion analysis and exact mass measurements, employing finally also selective deuterium labelling. The inclusion of the substituted aryl ring moiety appears to be important for the fragmentation of the aryloxymethylquinoxalines. A molecular ion rearrangement is proposed for the observed loss of OH· and CHO· radicals. The influence of the different substituents on the aryl ring moiety on the rearrangement in the gas phase and on the resulting fragmentation was investigated. Copyright © 2001 John Wiley & Sons, Ltd. [source] Systematic Regulation of the Enzymatic Activity of Phenylacetaldoxime Dehydratase by Exogenous LigandsCHEMBIOCHEM, Issue 12 2006Katsuaki Kobayashi Dr. Abstract Phenylacetaldoxime dehydratase from Bacillus sp. OxB-1 (OxdB) contains a heme that acts as the active site for the dehydration reaction of aldoxime. Ferrous heme is the active form, in which the heme is five coordinate with His282 as a proximal ligand. In this work, we evaluated the functional role of the proximal ligand for the catalytic properties of the enzyme by "the cavity mutant technique". The H282G mutant of OxdB lost enzymatic activity, although the heme, which was five coordinate with a water molecule (or OH,) as an axial ligand, existed in the protein matrix. The enzymatic activity was rescued by imidazole or pyridine derivatives that acted as the exogenous proximal ligand. By changing the electron-donation ability of the exogenous ligand with different substituents, the enzymatic activity could be regulated systematically. The stronger the electron-donation ability of the exogenous ligand, the higher was the restored enzymatic activity. Interestingly, H282G OxdB with 2-methyl imidazole showed a higher activity than the wild-type enzyme. Kinetic analyses revealed that the proximal His regulated not only the affinity of substrate binding to the heme but also the elimination of the OH group from the substrate. [source] Effect of Core Twisting on Self-Assembly and Optical Properties of Perylene Bisimide Dyes in Solution and Columnar Liquid Crystalline PhasesCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2007Zhijian Chen Abstract A series of highly soluble and fluorescent core-twisted perylene bisimide dyes (PBIs) 3,a,f with different substituents at the bay area (1,6,7,12 positions of the perylene core) were synthesized and fully characterized by 1H,NMR, UV/Vis spectroscopy, MS spectrometry, and elemental analysis. The ,,, aggregation properties of these new functional dyes were investigated in detail both in solution and in condensed phase by UV/Vis and fluorescence spectroscopy, vapor pressure osmometry (VPO), differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction. Concentration-dependent UV/Vis measurements and VPO analysis revealed that these core-twisted ,-conjugated systems show distinct self-dimerization equilibria in apolar solvent methylcyclohexane (MCH) with dimerization constants between 1.3×104 and 30,M,1. The photoluminescence spectra of the dimers of PBIs 3,a,f exhibit bathochromic shifts of quite different magnitude which could be attributed to different longitudinal or rotational offsets between the dyes as well as differences in the respective ,,, stacking distance. In condensed state, quite a few of these PBIs form luminescent rectangular or hexagonal columnar liquid crystalline phases with low isotropization temperatures. The effects of the distortion of the , systems on their ,,, stacking and the optical properties of the resultant stacks in solution and in LC phases have been explored in detail. In one case (3,a) a particularly interesting phase change from crystalline into liquid crystalline could be observed upon annealing that was accompanied by a transformation from non-fluorescent H -type into strongly fluorescent J -type packing of the dyes. [source] Ruthenium-Catalyzed Asymmetric Epoxidation of Olefins Using H2O2, Part II: Catalytic Activities and MechanismCHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2006Man Kin Tse Dr. Abstract Asymmetric epoxidation of olefins with 30,% H2O2 in the presence of [Ru(pybox)(pydic)] 1 and [Ru(pyboxazine)(pydic)] 2 has been studied in detail (pybox=pyridine-2,6-bisoxazoline, pyboxazine=pyridine-2,6-bisoxazine, pydic=2,6-pyridinedicarboxylate). 35 Ruthenium complexes with sterically and electronically different substituents have been tested in environmentally benign epoxidation reactions. Mono-, 1,1-di-, cis - and trans -1,2-di-, tri-, and tetra-substituted aromatic olefins with versatile functional groups can be epoxidized with this type of catalyst in good to excellent yields (up to 100,%) with moderate to good enantioselectivies (up to 84,% ee). Additive and solvent effects as well as the relative rate of reaction with different catalysts have been established. It is shown that the presence of weak organic acids or an electron-withdrawing group on the catalyst increases the reactivity. New insights on the reaction intermediates and reaction pathway of the ruthenium-catalyzed epoxidation are proposed on the basis of density functional theory calculation and experiments. [source] On the Tacticity of Polynorbornenes with 5,6- endo Pendant Groups That Contain Substituted Aryl ChromophoresCHEMISTRY - AN ASIAN JOURNAL, Issue 6 2007Wei-Yu Lin Abstract Two dimers and a series of polymers with 5,6- endo pendant aryl groups that contain different substituents at the para positions were synthesized. The conformation and stereochemistry of the dimers and polymers were determined by nonlinear optical analysis (EFISH) as well as UV/Vis and 13C,NMR spectroscopy. The chemical shifts of C7 for the polymers appeared as two peaks in the 13C,NMR spectra when the substituents are electron-withdrawing groups. The percentage decrease in the relative extinction coefficient of the polymers, ,d, was linearly related to the Hammett constant ,. Polynorbornenes with electron-withdrawing substituents may adopt isotactic stereochemistry with all pendant groups aligned in one direction. The nature of the interactions between neighboring chromophores may be one of the most important factors in directing the stereoregularity and conformation of these polymers. The corresponding polymers derived from the exo isomers appeared to be less stereoregular. [source] | ||||||||||||||||||||||