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Successful Synthesis (successful + synthesis)
Selected AbstractsA tethered ascorbate-norepinephrine compound, 4-UT, displays long-acting adrenergic activity on rabbit aortic smooth muscleDRUG DEVELOPMENT RESEARCH, Issue 5 2008Robert Root-Bernstein Abstract We previously demonstrated that adrenergic and histaminergic receptors have an ascorbic acid (vitamin C) binding site on the first extracellular loop, immediately adjacent to the aminergic binding site. Binding of ascorbate to this site strongly potentiates any sub-maximal dose of an adrenergic or histaminergic compound, significantly increasing its duration of activity. We report here the successful synthesis of a tethered compound that mimics the combined effects of a mixture of ascorbate with norepinephrine. The tethered compound uses a four-unit polyethylene linker to tether ascorbate to norepinephrine. The tethered compound is about tenfold less effective than norepinephrine in stimulating rabbit aortic smooth muscle, but has a very significantly enhanced duration of activity compared with norepinephrine alone and comparable to a mixture of norepinephrine and ascorbate. Additional ascorbate does not enhance the tethered compound's effects and we demonstrate that the compound binds to a synthetic peptide spanning the ascorbate binding site of the receptor. These experiments strongly suggest that the compound binds to both the adrenergic binding site and the ascorbate binding site simultaneously. Tethered compounds with linkers of other lengths did not have these properties. We believe that the synthesis of enhanced adrenergic and histaminergic drugs by tethering them to potentiators such as ascorbate will permit a new class of potential drugs to be created with high specificity and long duration of activity. Drug Dev Res 69:242,250, 2008. © 2008 Wiley-Liss, Inc. [source] Promising Functional Materials Based on Ladder Polysiloxanes,ADVANCED MATERIALS, Issue 15 2008Qilong Zhou Abstract Preparation of real ladder polysiloxanes (LPSs), including both oxygen-bridged ladder polysilsesquioxanes (LPSQs) and organo-bridged ladder polysiloxanes (OLPSs), had been a great challenge to polymer chemists from 1960 until the successful synthesis of LPSs via the supramolecular architecture-directed stepwise coupling polymerization (SCP) in the early 1980s. This opened up a new field of LPS-based advanced materials. As key building blocks, LPSs are used to construct a variety of polysiloxanes with special steric configurations and functions, such as mesomorphic LPSs, tubular polysiloxanes (TPs), and pseudo-sieve-plate polysiloxanes (pseudo-SPSs). With excellent temperature and radiation resistance, good solubility, and fine optical and mechanical properties, all these polysiloxanes demonstrate very promising prospects in the advanced materials realm. Here, the synthesis of well-ordered LPSs is presented and features of fishbone-like and rowboat-like liquid crystalline polysiloxanes are discussed. Special emphasis is given to typical applications of LPSs, TPSs, and pseudo-SPSs in the areas of liquid crystal displays, microelectronics packaging, and nonlinear optical materials. [source] Carbon-Carbon Double Bond versus Carbonyl Group Hydrogenation: Controlling the Intramolecular Selectivity with Polyaniline-Supported Platinum CatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2008Martin Steffan Abstract The use of polyaniline (PANI) as catalyst support for heterogeneous catalysts and their application in chemical catalysis is hitherto rather poorly known. We report the successful synthesis of highly dispersed PANI-supported platinum catalysts (particle sizes between 1.7 and 3.7,nm as revealed by transmission electron microscopy, TEM) choosing two different approaches, namely (i) deposition-precipitation of H2PtCl6 onto polyaniline, suspended in basic medium (DP method) and, (ii) immobilization of a preformed nanoscale platinum colloid on polyaniline (sol-method). The PANI-supported platinum catalysts were applied in the selective hydrogenation of the ,,,-unsaturated aldehyde citral. In order to benchmark their catalytic performance, citral hydrogenation was also carried out by using platinum supported on the classical support materials silica (SiO2), alumina (Al2O3), active carbon and graphite. The relations of the structural characteristics and surface state of the catalysts with respect to their hydrogenation properties have been probed by EXAFS and XPS. It is found that the DP method yields chemically prepared PtO2 on polyaniline and, thus, produces a highly dispersed and immobilized Adams catalyst (in the ,-PtO2 form) which is able to efficiently hydrogenate the conjugated CC bond of citral (selectivity to citronellal=87%), whereas reduction of the CO group occurs with polyaniline-supported platinum (selectivity to geraniol/nerol=78%) prepared via the sol-method. The complete reversal of the selectivity between the preferred hydrogenation of the conjugated CC or CO group is not only particularly useful for the selective hydrogenation of ,,,-unsaturated aldehydes but also unveils the great potential of conducting polymer-supported precious metals in the field of hitherto barely investigated chemical catalysis. [source] Reduction-Sensitive Self-Aggregates as a Novel Delivery SystemMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 8 2010Ju Eun Kim Abstract Methoxy PEG amine with molecular weight of 5k and , -caprolactone with molecular weight of 1,960 were conjugated to a peptide comprising three cysteine residues. The shift of peak molecular weight and narrow molecular weight distribution in GPC trace without any noticeable shoulder as well as 1H NMR analysis confirmed the successful synthesis of the copolymer. A modified O/W dialysis system was employed to prepare self-aggregates having the size around 210,nm. During the dialysis, stabilized aggregates were obtained by intermolecular disulfide bonds via oxidation. Critical aggregate concentration (CAC) of the copolymer was determined as 0.07,mg,·,mL,1 and disulfide-stabilized self-aggregates remained stable regardless of the concentration without displaying CAC. Doxorubicin-loading amount and efficiency was 8.7 and 26.0%, respectively. Release profile of doxorubicin below CAC at 37,°C showed a sustained release and the addition of D,L -dithiothreitol (DTT) after 24,h triggered a burst release of doxorubicin. Intermolecular disulfide bonds via oxidation stabilized the polymeric aggregates even in the diluted condition similar to that in the bloodstream and addition of DTT destabilized the aggregates to burst encapsulated doxorubicin in the reductive condition. [source] High-Speed Living Polymerization of Polar Vinyl Monomers by Self-Healing Silylium CatalystsCHEMISTRY - A EUROPEAN JOURNAL, Issue 34 2010Dr. Yuetao Zhang Abstract This contribution describes the development and demonstration of the ambient-temperature, high-speed living polymerization of polar vinyl monomers (M) with a low silylium catalyst loading (, 0.05,mol,% relative to M). The catalyst is generated in situ by protonation of a trialkylsilyl ketene acetal (RSKA) initiator (I) with a strong Brønsted acid. The living character of the polymerization system has been demonstrated by several key lines of evidence, including the observed linear growth of the chain length as a function of monomer conversion at a given [M]/[I] ratio, near-precise polymer number-average molecular weight (Mn, controlled by the [M]/[I] ratio) with narrow molecular weight distributions (MWD), absence of an induction period and chain-termination reactions (as revealed by kinetics), readily achievable chain extension, and the successful synthesis of well-defined block copolymers. Fundamental steps of activation, initiation, propagation, and catalyst "self-repair" involved in this living polymerization system have been elucidated, chiefly featuring a propagation "catalysis" cycle consisting of a rate-limiting CC bond formation step and fast release of the silylium catalyst to the incoming monomer. Effects of acid activator, catalyst and monomer structure, and reaction temperature on polymerization characteristics have also been examined. Among the three strong acids incorporating a weakly coordinating borate or a chiral disulfonimide anion, the oxonium acid [H(Et2O)2]+[B(C6F5)4], is the most effective activator, which spontaneously delivers the most active R3Si+, reaching a high catalyst turn-over frequency (TOF) of 6.0×103,h,1 for methyl methacrylate polymerization by Me3Si+ or an exceptionally high TOF of 2.4×105,h,1 for n -butyl acrylate polymerization by iBu3Si+, in addition to its high (>90,%) to quantitative efficiencies and a high degree of control over Mn and MWD (1.07,1.12). An intriguing catalyst "self-repair" feature has also been demonstrated for the current living polymerization system. [source] Mixed-Transition-Metal Acetylides: Synthesis and Characterization of Complexes with up to Six Different Transition Metals Connected by Carbon-Rich Bridging UnitsCHEMISTRY - A EUROPEAN JOURNAL, Issue 16 2008Rico Packheiser Dipl.-Chem. Abstract The synthesis and reaction chemistry of heteromultimetallic transition-metal complexes by linking diverse metal-complex building blocks with multifunctional carbon-rich alkynyl-, benzene-, and bipyridyl-based bridging units is discussed. In context with this background, the preparation of [1-{(,2 -dppf)(,5 -C5H5)RuCC}-3-{(tBu2bpy)(CO)3ReCC}-5-(PPh2)C6H3] (10) (dppf=1,1,-bis(diphenylphosphino)ferrocene; tBu2bpy=4,4,-di- tert -butyl-2,2,-bipyridyl; Ph=phenyl) is described; this complex can react further, leading to the successful synthesis of heterometallic complexes of higher nuclearity. Heterotetrametallic transition-metal compounds were formed when 10 was reacted with [{(,5 -C5Me5)RhCl2}2] (18), [(Et2S)2PtCl2] (20) or [(tht)AuCC-bpy] (24) (Me=methyl; Et=ethyl; tht=tetrahydrothiophene; bpy=2,2,-bipyridyl-5-yl). Complexes [1-{(,2 -dppf)(,5 -C5H5)RuCC}-3-{(tBu2bpy)(CO)3ReCC}-5-{PPh2RhCl2(,5 -C5Me5)}C6H3] (19), [{1-[(,2 -dppf)(,5 -C5H5)RuCC]-3-[(tBu2bpy)(CO)3ReCC]-5-(PPh2)C6H3}2PtCl2] (21), and [1-{(,2 -dppf)(,5 -C5H5)RuCC}-3-{(tBu2bpy)(CO)3ReCC}-5-{PPh2AuCC-bpy}C6H3] (25) were thereby obtained in good yield. After a prolonged time in solution, complex 25 undergoes a transmetallation reaction to produce [(tBu2bpy)(CO)3ReCC-bpy] (26). Moreover, the bipyridyl building block in 25 allowed the synthesis of Fe-Ru-Re-Au-Mo- (28) and Fe-Ru-Re-Au-Cu-Ti-based (30) assemblies on addition of [(nbd)Mo(CO)4] (27), (nbd=1,5-norbornadiene), or [{[Ti](,-,,,-CCSiMe3)2}Cu(NCMe)][PF6] (29) ([Ti]=(,5 -C5H4SiMe3)2Ti) to 25. The identities of 5, 6, 8, 10,12, 14,16, 19, 21, 25, 26, 28, and 30 have been confirmed by elemental analysis and IR, 1H, 13C{1H}, and 31P{1H} NMR spectroscopy. From selected samples ESI-TOF mass spectra were measured. The solid-state structures of 8, 12, 19 and 26 were additionally solved by single-crystal X-ray structure analysis, confirming the structural assignment made from spectroscopy. [source] The Mechanism of Formation of Amide-Based Interlocked Compounds: Prediction of a New Rotaxane-Forming MotifCHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2004David A. Leigh Prof. Abstract Molecular modeling of four different reagent systems shows that the (free) energies of supramolecular interactions in the gas phase and in solution can explain the different reaction products (i.e., various sized macrocycles, catenanes, and linear oligomers) that are formed in classic amide-catenane-forming reactions. Self-assembly of the catenanes requires the formation of ordered intertwined chains and is driven by bifurcated hydrogen bonds, with , stacking only playing a lesser role. The understanding gained from the computational study was used to predict the possibility of a new rotaxane-forming system that does not permit catenane formation. The predictions were confirmed by the successful synthesis and characterization (including X-ray crystallography) of two novel rotaxanes. [source] Enantioselective Synthesis of Non-Natural Aromatic ,-Amino AcidsCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2004Andreas Krebs Abstract We present two complementary methods for the stereoselective synthesis of non-natural ,-amino acids with aromatic or heteroaromatic side chains. One approach is based on the chemical transformation of methionine, whereas the other applies the stereoselective Myers alkylation of glycine. The resulting product types differ in the linker length between glycine and the aromatic substituent. Since methionine and pseudoephedrine are available in both absolute configurations, R - or S -configured enantiopure amino acids with either C2 or C3 linkers can be obtained on gram scales. In each case the key step of the synthesis is hydroboration of the unsaturated building blocks 9 and 17, followed by palladium-catalyzed Suzuki cross-coupling with aryl halides. Attention must in certain cases be paid to the stereochemical integrity when basic Suzuki conditions are applied. Our initial difficulties are reported as well as the final "racemization-proof" procedures. The protecting groups chosen for the ,-amino acids should be compatible with solid-phase peptide synthesis. This was confirmed by the successful synthesis of a series of tripeptides. [source] Synthesis of Large-Pore Urea-Bridged Periodic Mesoporous OrganosilicasCHEMISTRY - AN ASIAN JOURNAL, Issue 4 2009Ling Gao Abstract Bringing order: A new class of periodic mesoporous organosilicas (PMOs) with a urea-bridged organosilica precursor under acid-catalyzed and inorganic-salt-assisted conditions was obtained. The large-pore hybrid materials have ordered mesostructure with uniform pore size distributions, which can be seen from the TEM images. In this article we report the successful synthesis of a new class of periodic mesoporous organosilicas (PMOs) with a urea-bridged organosilica precursor under acid-catalyzed and inorganic-salt-assisted conditions. The large-pore hybrid materials have an ordered mesostructure with uniform pore size distributions, excellent thick framework walls, thermal stability, and specific functional groups. The composition of the mesoporous organosilicas was characterized by FTIR spectroscopy, 13C cross-polarization magic-angle spinning (CP,MAS) NMR spectroscopy, and 29Si MAS NMR spectroscopy. [source] | |||||||||||||