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Gem
Selected AbstractsSynthesis and in vitro cytotoxic activity on human anaplastic thyroid cancer cells of lipoamino acid conjugates of gemcitabineDRUG DEVELOPMENT RESEARCH, Issue 5 2010Rosario Pignatello Abstract Lipophilic derivatives of the antitumor drug gemcitabine (GEM) with the potential for improving drug loading in lipid-based colloidal carriers, like liposomes or lipid nanoparticles, are described. GEM free base was conjugated to lipoamino acids bearing an alkyl side chain of different length, by either a carbodiimide-assisted or an ethylchloroformiate-assisted coupling reaction, to obtain N4 -acyl GEM derivatives. These compounds retained the same in vitro cell growth inhibitory activity of the parent drug against two lines of human anaplastic thyroid cancer cells. Stability studies suggested that the observed activity was due mainly to intact derivatives and not to released GEM. Accordingly, these amphiphilic derivatives can be proposed in a further step for the encapsulation in liposomes or lipid nanocarriers, to achieve as a final goal an improvement of the pharmacokinetics and therapeutic activity of GEM. Drug Dev Res 2010. © 2010 Wiley-Liss, Inc. [source] Adhesion and Percolation Parameters in Two Dimensional Pd,LSCM Composites for SOFC Anode Current CollectionADVANCED FUNCTIONAL MATERIALS, Issue 5 2010Samir Boulfrad Abstract This paper is concerned with palladium,(La0.75Sr0.25)0.97Cr0.5Mn0.5O3 (LSCM) composite current collectors for solid oxide fuel cells (SOFCs); the composites, which are in a 2D configuration (thickness of about 8,10,µm), are deposited upon an LSCM electrode layer on top of an yttria zirconia electrolyte substrate. The influence of the LSCM particle size on the adhesion between palladium and LSCM are reported and discussed. Compositions using four different LSCM particle sizes (0.21, 0.49, 0.64, and 0.81,µm) with sintered Pd particle sizes approaching 10,µm are investigated. The best bonding is obtained when smaller particles are used. The electrical dc conductivity of the composite is reported as a function of the palladium volume fraction for all used LSCM particle sizes. The measured experimental values present typical insulating,conductive percolation. However, the transition occurs at ,33% of the conductive phase, that is, a lower percentage than for 2D ideal systems and a higher percentage than for 3D ideal systems. This is consistent with lower-dimension percolation for a system of large-grained conductors and small-grained insulators. The general effective media (GEM) equation is used to fit the experimental data, and the two main parameters (the threshold point ,c and the exponent t) are defined. [source] Conformational search of peptides and proteins: Monte Carlo minimization with an adaptive bias method applied to the heptapeptide deltorphinJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 4 2004S. Banu Ozkan Abstract The energy function of a protein consists of a tremendous number of minima. Locating the global energy minimum (GEM) structure, which corresponds approximately to the native structure, is a severe problem in global optimization. Recently we have proposed a conformational search technique based on the Monte Carlo minimization (MCM) method of Li and Scheraga, where trial dihedral angles are not selected at random within the range [,180°,180°] (as with MCM) but with biased probabilities depending on the increased structure-energy correlations as the GEM is approached during the search. This method, called the Monte Carlo minimization with an adaptive bias (MCMAB), was applied initially to the pentapeptide Leu-enkephalin. Here we study its properties further by applying it to the larger peptide with bulky side chains, deltorphin (H-Tyr-D-Met-Phe-His-Leu-Met-Asp-NH2). We find that on average the number of energy minimizations required by MCMAB to locate the GEM for the first time is smaller by a factor of approximately three than the number required by MCM,in accord with results obtained for Leu-enkephalin. © 2004 Wiley Periodicals, Inc. J Comput Chem 25: 565,572, 2004 [source] International inequality in well-beingJOURNAL OF INTERNATIONAL DEVELOPMENT, Issue 4 2004Mark McGillivray This paper examines inter-country inequality in indicators of human well-being. It is primarily concerned with inequality in two gender-related, composite indicators of development levels proposed: the Gender-related Development Index (GDI) and the Gender Empowerment Measure (GEM). A number of inequality indices are calculated using data for the period 1992 to 1998. A special interest of the paper is whether the GDI and GEM tell different stories with respect to inequality than the Human Development Index (HDI) and PPP GDP per capita. Results indicate that the answer to this question with respect to PPP GDP per capita is a qualified yes, being dependent on how this variable is measured. Other results indicate that the GEM and GDI exhibit slightly higher inequality than the HDI. Copyright © 2004 John Wiley & Sons, Ltd. [source] Down-regulation of members of glycolipid-enriched membrane raft gene family, MAL and BENE, in cervical squamous cell cancersJOURNAL OF OBSTETRICS AND GYNAECOLOGY RESEARCH (ELECTRONIC), Issue 1 2004Mitsuko Hatta Abstract Persistent human papillomavirus infections cause infected epithelial cells to lose cellular polarity leading to cell transformation. Glycolipid-enriched membrane (GEM) rafts are implicated in polarized sorting of apical membrane proteins in epithelial cells and even in signal transduction. The MAL and BENE are essential component of the GEM raft's machinery for apical sorting of membrane proteins. In this study we demonstrated down-regulation of MAL and BENE mRNA in over two-thirds of primary cervical squamous cell cancers (14 and 15 of 20 cases, for MAL and BENE, respectively) when compared to corresponding non-cancerous uterine squamous cells. Allelic loss or hyper-methylation was not accompanied by MAL or BENE mRNA down-expression in human primary cervical cancers in microsatellite allelic analysis and HpaII-PCR-based methylation analysis of the MAL and BENE genomic region. In addition, we note down-regulation of these genes in established cervical cancer cell lines. These results suggest that down-regulation of MAL and BENE genes, which are essential components of the cellular polarized sorting system, play an important role in human cervical squamous cell cancer development. [source] Green element method for 2D Helmholtz and convection diffusion problems with variable velocity coefficientsNUMERICAL METHODS FOR PARTIAL DIFFERENTIAL EQUATIONS, Issue 2 2005Okey Oseloka Onyejekwe Abstract Computation of 2D Helmholtz and transient convection diffusion problems with linear reaction and variable velocity components are implemented with the Green element method (GEM). GEM's fundamental solution which is derived from the diffusion differential operator simplifies the numerical procedure considerably, and together with the Green's second identity, an element to element treatment of the inhomogeneous terms is guaranteed. The reported numerical experiments reveal that the method can be relied on to yield faithful results. © 2004 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2005 [source] NSOM- and AFM-based nanotechnology elucidates nano-structural and atomic-force features of a Y. pestis V immunogen-containing particle vaccine capable of eliciting robust responsePROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 6 2009Gucheng Zeng Abstract It is postulated that unique nanoscale proteomic features of immunogen on vaccine particles may determine immunogen-packing density, stability, specificity, and pH-sensitivity on the vaccine particle surface and thus impact the vaccine-elicited immune responses. To test this presumption, we employed near-filed scanning optical microscopy (NSOM)- and atomic force microscopy (AFM)-based nanotechnology to study nano-structural and single-molecule force bases of Yersinia pestis (Y. pestis) V immunogen fused with protein anchor (V-PA) loaded on gram positive enhancer matrix (GEM) vaccine particles. Surprisingly, the single-molecule sensitive NSOM revealed that ,90% of V-PA immunogen molecules were packed as high-density nanoclusters on GEM particle. AFM-based single-molecule force analyses indicated a highly stable and specific binding between V-PA and GEM at the physiological pH. In contrast, this specific binding was mostly abrogated at the acidic pH equivalent to the biochemical pH in phagolysosomes of antigen-presenting-cells in which immunogen protein is processed for antigen presentation. Intranasal mucosal vaccination of mice with such immunogen loaded on vaccine particles elicited robust antigen-specific immune response. This study indicated that high-density, high-stability, specific, and immunological pH-responsive loading of immunogen nanoclusters on vaccine particles could readily be presented to the immune system for induction of strong antigen-specific immune responses. [source] GM1,/,GD1b,/,GA1 synthase expression results in the reduced cancer phenotypes with modulation of composition and raft-localization of gangliosides in a melanoma cell lineCANCER SCIENCE, Issue 9 2010Yu Dong Gangliosides are expressed in neuroectoderm-derived tumors, and seemed to play roles in the regulation of cancer properties. To examine the behavior and roles of individual gangliosides, GM1/GD1b/GA1 synthase cDNA was introduced into the melanoma cell line SK-MEL-37, and changes in tumor phenotypes were analyzed. The transfectant cells showed neo-expression of GD1b, GT1b, and GM1, and reduced expression of GM3, GM2, GD2, and GD3. Function analyses revealed that the transfectant cells had definite reduction in cell growth and invasion. Tyrosine-phosphorylation levels of proteins such as p130Cas and paxillin were also reduced in the transfectants. These results suggested that the expression of GM1/GD1b/GA1 synthase resulted in the suppression of tumor properties. In the analyses of the floating patterns of gangliosides using fractions from sucrose density gradient ultracentrifugation of TritonX-100 extracts, the majority of gangliosides were found in glycolipid-enriched microdomain (GEM)/raft fractions, while GD3, GD1b, and GT1b in the transfectant cells tended to disperse to non-GEM/raft fractions. Furthermore, GD3, GD1b, and GT1b in non-GEM/raft dominantly had unsaturated fatty acids, while those in GEM/rafts contained more saturated forms than in non-GEM/rafts. This might be a mechanism for the decreased tumor properties in the transfectants of GM1/GD1b/GA1 synthase cDNA. (Cancer Sci 2010) [source] Analytical SuperSTEM for extraterrestrial materials researchMETEORITICS & PLANETARY SCIENCE, Issue 10 2009John P. Bradley The improved technical capabilities enable analyses previously not possible. Mineral structures can be directly imaged and analyzed with single-atomic-column resolution, liquids, and implanted gases can be detected, and UV-VIS optical properties can be measured. Detection limits for minor/trace elements in thin (<100 nm thick) specimens are improved such that quantitative measurements of some extend to the sub-500 ppm level. Electron energy-loss spectroscopy (EELS) can be carried out with 0.10,0.20 eV energy resolution and atomic-scale spatial resolution such that variations in oxidation state from one atomic column to another can be detected. Petrographic mapping is extended down to the atomic scale using energy-dispersive X-ray spectroscopy (EDS) and energy-filtered transmission electron microscopy (EFTEM) imaging. Technical capabilities and examples of the applications of SuperSTEM to extraterrestrial materials are presented, including the UV spectral properties and organic carbon K-edge fine structure of carbonaceous matter in interplanetary dust particles (IDPs), X-ray elemental maps showing the nanometer-scale distribution of carbon within GEMS (glass with embedded metal and sulfides), the first detection and quantification of trace Ti in GEMS using EDS, and detection of molecular H2O in vesicles and implanted H2 and He in irradiated mineral and glass grains. [source] A weak lensing estimate from GEMS of the virial to stellar mass ratio in massive galaxies to z, 0.8MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2006Catherine Heymans ABSTRACT We present constraints on the evolution of the virial to stellar mass ratio of galaxies with high stellar masses in the redshift range 0.2 < z < 0.8, by comparing weak lensing measurements of virial mass Mvir with estimates of stellar mass Mstar. For a complete sample of galaxies with log (Mstar/M,) > 10.5, where the majority show an early-type morphology, we find that the virial mass to stellar mass ratio is given by Mvir/Mstar= 53+13,16. Assuming a baryon fraction from the concordance cosmology, this corresponds to a stellar fraction of baryons in massive galaxies of ,*b/,b= 0.10 ± 0.03. Analysing the galaxy sample in different redshift slices, we find little or no evolution in the virial to stellar mass ratio, and place an upper limit of ,2.5 on the growth of massive galaxies through the conversion of gas into stars from z= 0.8 to the present day. [source] Defining Accountability Up: the Global Economic MultilateralsGOVERNMENT AND OPPOSITION, Issue 2 2004Miles Kahler Critics of the global economic multilaterals (GEMs) , the International Monetary Fund, the World Bank, and the World Trade Organization , allege that these organizations fail the test of democratic accountability. Two distinct measures of democratic accountability have been applied to the GEMs. To the degree that these organizations display ,accountability deficits', those deficiencies are the result of choices by the most influential national governments. Three techniques have been deployed to enhance the accountability of the GEMs: transparency (more information for those outside the institution), competition (imitation of democratic accountability) and changes in rules of representation (accountability to stakeholders rather than shareholders). Each of these may impose costs, however, and may conflict with other valued aims of the organizations. [source] Suicidal genetically engineered microorganisms for bioremediation: Need and perspectivesBIOESSAYS, Issue 5 2005Debarati Paul In the past few decades, increased awareness of environmental pollution has led to the exploitation of microbial metabolic potential in the construction of several genetically engineered microorganisms (GEMs) for bioremediation purposes. At the same time, environmental concerns and regulatory constraints have limited the in situ application of GEMs, the ultimate objective behind their development. In order to address the anticipated risks due to the uncontrolled survival/dispersal of GEMs or recombinant plasmids into the environment, some attempts have been made to construct systems that would contain the released organisms. This article discusses the designing of safer genetically engineered organisms for environmental release with specific emphasis on the use of bacterial plasmid addiction systems to limit their survival thus minimizing the anticipated risk. We also conceptualize a novel strategy to construct "Suicidal Genetically Engineered Microorganisms (SGEMs)" by exploring/combining the knowledge of different plasmid addiction systems (such as antisense RNA-regulated plasmid addiction, proteic plasmid addiction etc.) and inducible degradative operons of bacteria. BioEssays 27:563,573, 2005. © 2005 Wiley Periodicals, Inc. [source] X-ray spectroscopy of the intermediate polar PQ GemMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2002Cynthia H. James Abstract Using RXTE and ASCA data, we investigate the roles played by occultation and absorption in the X-ray spin pulse profile of the intermediate polar PQ Gem. From the X-ray light curves and phase-resolved spectroscopy, we find that the intensity variations are the result of a combination of varying degrees of absorption and the accretion regions rotating behind the visible face of the white dwarf. These occultation and absorption effects are consistent with those expected from the accretion structures calculated from optical polarization data. We can reproduce the changes in absorber covering fraction either from geometrical effects, or by considering that the material in the leading edge of the accretion curtain is more finely fragmented than in other parts of the curtain. We determine a white dwarf mass of , 1.2 using the RXTE data. [source] Isolation of two microsatellite markers from BAC clones of the Vf scab resistance region and molecular characterization of scab-resistant accessions in Malus germplasm,PLANT BREEDING, Issue 4 2004B. A. Vinatzer Abstract A polymerase chain reaction (PCR)-based method was developed to isolate microsatellite markers from large-insert genomic DNA clones of bacterial artificial chromosome (BAC) libraries. The method is fast and economic since it does not require subcloning. It was applied to isolate a microsatellite marker from a BAC clone of the chromosomal region containing the apple scab resistance gene Vf. The Vf gene of Malus floribunda 821 is the most widely used source of scab resistance in apple breeding. A second microsatellite was found on the extremity of a BAC clone flanking the Vf locus. The two microsatellites allowed the identification of the presence of the Vf gene in the scab-resistant accessions M. micromalus SA573-3, ,Golden Gem', M. prunifolia 19651 and MA 16 not previously known to carry this gene. They were also used to verify the correctness of the published genealogical tree of the Vf cultivar ,Florina', in which a probable mistake was identified. This analysis shows the importance of genotyping the Vf locus when choosing scab-resistant germplasm as parents in breeding programmes. [source] The Athletic Crusade: Sport and American Cultural Imperialism By Gerald R. GemsHISTORY, Issue 312 2008FRANK COGLIANO No abstract is available for this article. [source] The Athletic Crusade by Gerald R. GemsTHE JOURNAL OF AMERICAN CULTURE, Issue 2 2007Eldon E. Snyder No abstract is available for this article. [source] Anaerobic transformation of compounds of technical toxaphene.ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 11 2003Abstract Technical toxaphene (Melipax) and the single compounds of technical toxaphene (CTTs) 2,2,5- endo, 6- exo, 8,8,9,10- octachlorobornane (B8-806), 2,2,5- endo, 6- exo, 8,9,9,10-octachlorobornane (B8-809), 2,2,5,5,8,9,9,10,10-nonachlorobornane (B9- 1025), 2- endo, 3- exo, 5- endo, 6- exo, 8,8,9,10,10-nonochlorobornane (B9-1679), 2- endo, 3- exo, 5- endo, 6- exo, 8,9,10,10-octachlorobornane (B8-1414), 2- endo, 3- exo, 5- endo, 6- exo, 8,8,9,10-octachlorobornane (B8-1412), and 2- exo, 3- endo, 5- exo, 9,9,10,10-heptachlorobornane (B7-1453) were treated with suspensions of the anaerobic bacterium Dehalospirillum multivorans. After 7 d, more than 50% of technical toxaphene was transformed, and the relative amount of early eluting CTTs increased. After 16 d, only 2- exo, 3- endo, 6- exo, 8,9,10-hexachlorobornane (B6-923), 2- endo, 3- exo, 5- endo, 6- exo, 8,9,10-heptachlorobornane (B7-1001), and a few minor penta- and hexachloro-CTTs were detected in the samples. The result of the transformation was comparable with observations in naturally contaminated sediments and soil. However, the performance with D. multivorans was more simple and reproducible, as well as faster, than use of soil, sediment, or anaerobic sewage sludge. In agreement with reports in the literature, reductive dechlorination at geminal chlorine atoms (gem -Cls) was found to be the major CTT transformation pathway. Experiments conducted with CTTs and gem -Cls at both primary and secondary carbons clarified that the initial Cl -> H substitution takes place at the secondary carbon C2. Furthermore, the 2- endo -Cl position was preferably substituted with hydrogen. In the case of B8-806, the dechlorination at the secondary carbon C2 was approximately 20-fold faster than the subsequent, slow reduction at the primary carbon C8. The three different formerly unknown heptachloro-CTTs, 2- exo, 3- endo, 6- exo, 8,9,9,10-heptachlorobornane (B7-1473), 2- exo, 3- endo, 6- endo, 8,9,9,10-hepatchlorobornane (B7-1461), and 2- exo, 3- endo, 6- exo, 8,8,9,10-heptachlorobornane (B7-1470) were found as intermediates of the B8-806/809 transformation. Treatment of B9-1679 with D. multivorans indicated that gem -Cls on the bridge (C8 and C9) are dechlorinated faster than gem -Cls on the bridgehead (C10). [source] Stereoselective Disposition of the Geminal Dimethyl Group in the Cyclization of Geranyl Acetate under Zeolite Confinement ConditionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 19 2006Constantinos Tsangarakis Abstract The stereochemistry in the acid-catalysed biomimetic cyclization of [8,8,8-D3]geranyl acetate was examined in solution and under conditions of zeolite Y confinement. In the intrazeolite reaction the gem -allylic methyl group adopts a diastereoselective disposition in the cyclization product (64,% dr). In contrast, the gem -dimethyl disposition in a homogeneous medium (ClSO3H/2-nitropropane) proceeds with negligible diastereoselectivity (dr < 5,%). The enhanced diastereoselection within the zeolite is attributed to the proximity of the nucleophilic double bond to the intermediate carbocation, as a result of confinement (entropy effect). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] One-Pot Preparation of [n]Ladderanes by [2, + 2,] PhotocycloadditionEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 3 2005Henning Hopf Abstract A new method for the preparation of [n]ladderanes is presented, based on a one-pot [2,+2,] photocycloaddition of [2.2]paracyclophane pseudo- gem bis(polyene) precursors. [3]- and [5]ladderanes could be isolated and were fully characterized, including their X-ray structure analysis. The overall chemical yields from [2.2]paracyclophane as starting material were found to be 53 % ([3]ladderane) and 38 % ([5]ladderane). Preliminary investigations of their photochromic properties (reversible change from yellow or red to colourless forms) are described. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Reinvestigation of the Mechanism of gem -Diacylation: Chemoselective Conversion of Aldehydes to Various gem -Diacylates and Their Cleavage under Acidic and Basic ConditionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 2 2005Veerababurao Kavala Abstract The mechanism of gem -diacylate formation has been studied extensively using tetrabutylammonium tribromide (TBATB) as the catalyst. The reaction proceeds by a nucleophilic attack of an anhydride on an aldehydic carbonyl group, nucleophilic attack of the hemiacylate intermediate on a second molecule of the anhydride, followed by an intermolecular attack of a second acetate group to regenerate the anhydride. gem -Diacylates of various aliphatic and aromatic aldehydes were obtained directly from the reaction of a variety of aliphatic and aromatic acid anhydrides in the presence of a catalytic quantity of tetrabutylammonium tribromide (TBATB) under solvent-free conditions. A significant electronic effect was observed during its formation as well as deprotection to the corresponding aldehyde. Chemoselective gem -diacylation of the aromatic aldehyde containing an electron-donating group has been achieved in the presence of an aldehyde containing an electron-withdrawing group. Deprotection of the gem -diacylate to the parent carbonyl compound can be accomplished in methanol in presence of the same catalyst. Here again, chemoselective deprotection of the gem -diacylate of a substrate containing an electrondonating group has been achieved in the presence of a substrate containing an electron-withdrawing group. Both the acid and base stability order of the various gem -diacylates examined follow a similar order. The stability order determined from the present study is: gem -dibenzoate > gemdipivalate > gem -diisobutyrate > gem -diacetate > gem -dipropionate. All the gem -diacylals are more stable under basic conditions than acidic condition. No correlation was found between the stability order and the pKa's of the corresponding acids; rather, the stability order is directly related to the steric crowding around the carbonyl carbon. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Chemoenzymatic Synthesis of (2S)- and (2R)-2-(1,3-Dithian-2-ylmethyl)oxiraneEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2004Eirik Sundby Abstract Lipase-catalyzed transesterifications and biological reductions were used to obtain the (S)-enantiomers of 3-chloro-1-(1,3-dithian-2-yl)-2-propanol and 1-(1,3-dithian-2-yl)-3-fluoro-2-propanol and their (R)-acetates. (S)-3-Chloro-1-(1,3-dithian-2-yl)-2-propanol and (R)-3-chloro-1-(1,3-dithian-2-yl)-2-propyl acetate were converted into the respective enantiomers of 2-(1,3-dithian-2-ylmethyl)oxirane. During this work we also isolated a new gem -disubstituted epoxide, 2-(chloromethyl)-2-(1,3-dithian-2-yl)oxirane. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] A Straightforward Synthesis of N -Functionalized ,-DiiminesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 2 2003Alexandrine Maraval Abstract Reaction of Schwartz's reagent [Cp2ZrHCl]n (1) (one or two equivalents) with gem -dinitrile compounds of the type X(CN)2 [X = CMe2, CBenz2, P(NiPr2)2] gives the corresponding mono- and di- N -zirconated imino complexes selectively. Substitution reactions of the zirconocene metal fragment with electrophiles such as, for example, chlorophosphanes of the type R2PCl, acid chlorides RC(O)Cl or the iminium salt [CH2NMe2]Cl allowed the preparation of a large variety of stable N -functionalized mono- and ,-diimine derivatives. The nature of the X group is of particular importance for the success of the substitution reaction step. The X-ray crystal structures obtained for the N -functionalized gem -aldimino-nitrile compounds 9, 10b, the N -phosphorylated ,-diimine 32, and the gem -formyl nitrile derivative 12b are presented. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Synthesis of Trisubstituted Pyrroles from Rhodium-Catalyzed Alkyne Head-to-Tail Dimerization and Subsequent Gold- Catalyzed CyclizationADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2009Hong Mei Peng Abstract Dimerization of N -protected propargylic amines in a rather rare head-to-tail mode has been achieved under mild conditions with high selectivity using rhodium catalysts. The N -protecting group could be a sulfonyl, carbamate, or carbonyl functionality and (cyclooctadiene)rhodium chloride dimer/1,1,-bis(diphenylphosphino)ferrocene {[Rh(COD)Cl]2/dppf} as well as tris(triphenylphosphine)rhodium chloride [Rh(PPh3)3Cl] proved to be active catalysts. In addition, these functionalized gem -enynes subsequently undergo selective gold(III)-catalyzed intramolecular hydroamination to give trisubstituted pyrroles under mild conditions. [source] Biocatalytic Asymmetric Dihydroxylation of Conjugated Mono- and Poly-alkenes to Yield Enantiopure Cyclic cis -DiolsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7-8 2005Derek Abstract Dioxygenase-catalysed asymmetric dihydroxylation, of a series of conjugated monoalkenes and polyenes, was found to yield the corresponding monols and 1,2-dihydrodiols. The diol metabolites were obtained from monosubstituted, gem -disubstituted, cis -disubstituted, and trisubstituted alkene substrates, using whole cells of Pseudomonas putida strains containing toluene and naphthalene dioxygenases. Dioxygenase selection and alkene type were established as important factors, in the preference for dioxygenase-catalysed 1,2-dihydroxylation of conjugated alkene or arene groups, and monohydroxylation at benzylic or allylic centres. Competition from allylic hydroxylation of methyl groups was observed only when naphthalene dioxygenase was used as biocatalyst. The structures, enantiomeric excess values and absolute configurations of the bioproducts, were determined by a combination of stereochemical correlation, spectroscopy (NMR and CD) and X-ray diffraction methods. cis -1,2-Diol metabolites from arenes, cyclic alkenes and dienes were generally observed to be enantiopure (>98% ee), while 1,2-diols from acyclic alkenes had lower enantiomeric excess values (<88% ee). The enantiopure cis -diol metabolite of a gem -disubstituted fulvene was used as precursor in a new chemoenzymatic route to a novel C2 -symmetrical ketone. [source] Organic cyclic difluoramino-nitramines: infrared and Raman spectroscopy of 3,3,7,7-tetrakis(difluoramino)octahydro 1,5-dinitro-1,5-diazocine (HNFX)JOURNAL OF RAMAN SPECTROSCOPY, Issue 8 2009Philippe F. Weck Abstract We present the first vibrational structure investigation of 3,3,7,7-tetrakis(difluoramino)octahydro-1,5-dinitro- 1,5-diazocine (HNFX),and, more generally, of a member of the new class of gem -bis(difluoramino)-substituted heterocyclic nitramine energetic materials,using combined theoretical and experimental approaches. Optimized molecular structure and vibrational spectra of the Ci, symmetry conformer constituting the HNFX crystal were computed using density functional theory methods. Fourier transform infrared and Raman spectra of HNFX crystalline samples were also collected at ambient temperature and pressure. The average deviation of calculated structural parameters from X-ray diffraction data is ,1% at the B3LYP/6-311 + + G(d,p) level of theory, suggesting the absence of significant molecular distortion induced by the crystal field. Very good agreement was found between simulated and measured spectra, allowing reliable assignment of the fundamental normal modes of vibration of the HNFX crystal. Detailed analysis of the normal modes of the C,(NF2)2 and N,NO2 moieties was performed due to their critical importance in the initial steps of the molecular homolytic fragmentation process. Copyright © 2009 John Wiley & Sons, Ltd. [source] 1H and 13C NMR assignments for new heterocyclic TAM leuco dyes, (2Z,2,E)-2,2,-(2-phenyl propane-1,3-diylidene) bis(1,3,3-trimethylindoline) derivatives.MAGNETIC RESONANCE IN CHEMISTRY, Issue 9 2008Part II Abstract The 1H and 13C NMR spectra of the novel heterocyclic Leuco-TAM dyes, (2Z, 2,E)-2,2,-(2-phenyl propane-1,3-diylidene) bis(1,3,3-trimethylindoline) derivatives 1,4 as precursors of triarylmethane (TAM)+ (Malachite Green FB-analog) dyes were completely assigned by 1D and 2D NMR experiments, including DEPT, COSY, HSQC, HMBC, and NOESY. Especially, the diastereotopic gem -dimethyl protons at the C3 and C3, positions of the FB rings were definitively assigned. The (Z,E) isomers adopt the energetically favored three-bladed propeller conformation in solution. Copyright © 2008 John Wiley & Sons, Ltd. [source] Spin,spin coupling and substituent and halogen isotope shift effects in the fluorine NMR spectra of fluorinated cyclopropanes and cyclopropyl ethersMAGNETIC RESONANCE IN CHEMISTRY, Issue 3 2007Wallace S. Brey Abstract The 19F NMR spectra of a series of fluorinated cyclopropanes, most of which contain chlorine or bromine on the ring, have been observed and analyzed. A scheme has been developed to assign the resonances and the molecular stereochemistry, based on substituent effects, comparison of related molecules, and isotope shifts induced by the halogens. Replacement of fluorine by chlorine shifts cis fluorine resonances to lower field, and bromine has an even greater downfield influence. However, the shift effect of bromine compared to chlorine on gem or trans fluorines is variable. The magnitude of the isotope shifts is found to be regularly related to the geometrical relationship of the halogen to the observed fluorine and thus makes a significant contribution to the fluorine assignments. The three-bond spin,spin coupling constants between fluorine atoms in cyclopropanes display unusual behavior and are not helpful for assignment of the fluorine resonances. The signs of the coupling constants have been investigated by spin-tickling experiments, and the previously developed relation of the coupling constant sign to its temperature dependence has been found to be violated for some molecules. Copyright © 2007 John Wiley & Sons, Ltd. [source] Electron ionisation mass spectral studies of bridgehead-fused ,2 -norbornanethiazolinesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 6 2009Antonio García Martínez The electron ionisation (EI) mass spectra of a series of bridgehead-fused ,2 -norbornanethiazolines, a new class of bridgehead-norbornane derivatives, have been studied and their cleavage mechanisms rationalised on the basis of the substituent shifts as well as on the identification of relevant peaks through accurate mass measurements and collision-induced dissociation tandem mass spectrometric experiments. The fragmentation patterns of isomeric pairs of 6,6- and 10,10-dimethylnorbornanethiazolines are almost identical, probably due to an initial isomerisation of molecular ion previous to the fragmentation. In general, the dominant peaks in the spectra of all the studied compounds originate from initial , -cleavages of C(5),C(6) or C(1),C(10) bonds, followed by concomitant homolytic cleavage of C(1),C(9) and C(7),C(10) bonds. The driving force for this fragmentation pathway, directed by the gem -dimethyl group, is the formation of a highly stabilised thiazolilmethyl cation which constitutes the base peak in all the spectra and allows the identification of these interesting ligands. Copyright © 2009 John Wiley & Sons, Ltd. [source] Stereoselective Synthesis of 2,6- cis -Tetrahydropyrans through a Tandem Allylic Oxidation/Oxa-Michael Reaction Promoted by the gem -Disubstituent Effect: Synthesis of (+)-Neopeltolide Macrolactone,ANGEWANDTE CHEMIE, Issue 41 2009Hyoungsu Kim Dr. Möglichst wenige Schutzgruppen werden in einer kurzen Synthese von (+)-Neopeltolid-Makrolacton verwendet, die auf der Titelreaktion sowie auf Dithiankupplungen beruht (siehe Schema). Die gem -Disubstitution durch die Dithianeinheit erleichtert die Oxa-Michael-Reaktion im Anschluss an die allylische Oxidation; somit wird effizient und hoch diastereoselektiv der 2,6- cis -Tetrahydropyranring erhalten. [source] gem -Dimethylcyclopropanation of dibenzylideneacetone using triisopropyl sulfoxonium tetrafluoroborateACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2009Michael G. Edwards The reaction between dibenzylideneacetone (dba) and triisopropyl sulfoxonium tetrafluoroborate has been reinvestigated. The stereochemistry of the major diasteromeric bis(gem -dimethylcyclopropane) adduct has now been assigned as [(1RS,3RS)-2,2-dimethyl-3-phenylcyclopropyl][(1SR,3SR)-2,2-dimethyl-3-phenylcyclopropyl]methanone, C23H26O, by X-ray crystallographic studies on a twinned crystal. The asymmetric unit contains two molecules of the adduct, the conformations of which differ in the orientation of the phenyl ring relative to the adjacent cyclopropanated double bond. The carbonyl groups of each adduct are aligned approximately along the a axis and in opposite directions to each other. The molecules pack to give a sinusoidal pattern along the b axis. This is the first acyclic bis(dimethylcyclopropyl) ketone for which an X-ray crystal structure determination has been reported, and is also the first bis-cyclopropanated dba analogue. The knowledge that the major diastereomer has the meso structure (and therefore the confirmation that the minor isomer is the racemate) will prove invaluable in future studies to utilize bis(dimethylcyclopropyl) ketones as reagents, in rearrangement processes, and as potential ligands and ligand precursors in organometallic chemistry. [source] | |||||||||||||||||||||||||||||||||||||||||||