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Barbara Ramsay Shaw - One of the best experts on this subject based on the ideXlab platform.
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Synthesis, Hydrolysis, and Protonation-Promoted Intramolecular Reductive Breakdown of Potential NRTIs: Stavudine α-P-Borano-γ-P-N-l-tryptophanyltriphosphates
MDPI AG, 2015Co-Authors: Barbara Ramsay ShawAbstract:Phosphorus-modified prodrugs of dideoxynucleoside triphosphates (ddNTPs) have shown promise as pronucleotide strategies for improving antiviral activity compared to their parent dideoxynucleosides. Borane modified NTPs offer a promising choice as nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs). However, the availability of α-P-Borano-γ-P-substituted NTP analogs remains limited due to challenges with synthesis and purification. Here, we report the chemical synthesis and stability of a new potential class of NRTI prodrugs: stavudine (d4T) 5′-α-P-Borano-γ-P-N-L-tryptophanyltriphosphates. One-pot synthesis of these compounds was achieved via a modified cyclic trimetaphosphate approach. Pure Rp and Sp diastereomers were obtained after HPLC separation. Based on LC-MS analysis, we report degradation pathways, half-lives (5–36 days) and mechanisms arising from structural differences to generate the corresponding Borano tri- and di-phosphates, and H-phosphonate, via several parallel routes in buffer at physiologically relevant pH and temperature. Here, the major hydrolysis products, d4T α-P-Boranotriphosphate Rp and Sp isomers, were isolated by HPLC and identified with spectral data. We first propose that one of the major degradation products, d4T H-phosphonate, was generated from the d4T pronucleotides via a protonation-promoted intramolecular reduction followed by a second step nucleophilic attack. This report could provide valuable information for pronucleotide-based drug design in terms of selective release of target nucleotides
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synthesis and properties of novel triphosphate analogues ribonucleoside and deoxyribonucleoside α p Borano α p thio triphosphates
Nucleosides Nucleotides & Nucleic Acids, 2001Co-Authors: Kenneth W Porter, Barbara Ramsay ShawAbstract:The first ribo- and deoxyribo-nucleoside (α-P-Borano, α-P-thio)triphosphates have been synthesized. The chemical and biochemical properties of adenosine (α-P-Borano, α-P-thio)triphosphate and thymidine (α-P-Borano, α-P-thio) triphosphate have been investigated.
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synthesis and properties of novel triphosphate analogues ribonucleoside and deoxyribonucleoside alpha p Borano alpha p thio triphosphates
Nucleosides Nucleotides & Nucleic Acids, 2001Co-Authors: Jinlai Lin, Kenneth W Porter, Barbara Ramsay ShawAbstract:The first ribo- and deoxyribo-nucleoside (alpha-P-Borano, alpha-P-thio)triphosphates have been synthesized. The chemical and biochemical properties of adenosine (alpha-P-Borano, alpha-P-thio)triphosphate and thymidine (alpha-P-Borano, alpha-P-thio) triphosphate have been investigated.
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synthesis of a novel triphosphate analogue nucleoside α p Borano α p thiotriphosphate
ChemInform, 2001Co-Authors: Jinlai Lin, Barbara Ramsay ShawAbstract:The first Boranothiotriphosphate compound, thymidine 5′-[α-P-Borano, α-P-thio]triphosphate, in which Borane and sulfur replace the two non-bridging oxygens of the α-phosphate in natural nucleoside triphosphates (NTPs), has been synthesized; some chemical properties of this Borane–sulfur disubstituted nucleoside triphosphate analogue have been investigated. The synthetic approach reported here should be applicable for preparation of any α-Borano, α-thio modified NTP or deoxy NTP; potential applications are discussed.
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synthesis and separation of diastereomers of ribonucleoside 5 alpha p Borano triphosphates
Journal of Organic Chemistry, 1998Co-Authors: Kaizhang He, Ahmad Hasan, Bozenna Krzyzanowska, Barbara Ramsay ShawAbstract:Nucleoside Boranophosphates, in which one of the phosphate oxygens is replaced by a Borane group, are isoionic and isoelectronic analogues of naturally occurring nucleotides. Boranophosphates also are biochemically important congeners of phosphorothioates and methylphosphonates. The authors have developed a convenient one-pot method to synthesize the set of ribonucleoside (A, U, G, and C) 5{prime}-({alpha}-P-Borano)triphosphates. Phosphitylation of the 2{prime},3{prime}-protected ribonucleoside with 2-chloro-4H-1,3,2-benzodioxaphosphorin-4-one gives the 5{prime}-phosphite intermediate 2 which undergoes in situ substitution in the presence of pyrophosphate to give the cyclic intermediate, P{sup 2},P{sup 3}-dioxo-P{sup 1}-ribonucleosidylcyclotriphosphate 3. Immediate oxidation of compound 3 with amine{center_dot}Borane complex results in ribonucleoside 5{prime}-({alpha}-P-Borano)cyclotriphosphate 4. Subsequent reaction of compound 4 with water followed by ammonium hydroxide yields the crude product as a diastereomeric mixture of ribonucleoside 5{prime}-({alpha}-P-Borano)triphosphate 6. Pure compound 6 is isolated in 30--45% overall yield using ion-exchange chromatography. The separation of two diastereomers of ribonucleoside 5{prime}-({alpha}-P-Borano)triphosphate 6 is achieved by reverse phase HPLC.
Saim Ozkar - One of the best experts on this subject based on the ideXlab platform.
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pvp stabilized nickel 0 nanoparticles as catalyst in hydrogen generation from the methanolysis of hydrazine Borane or ammonia Borane
Applied Catalysis B-environmental, 2015Co-Authors: Derya Ozhava, Nihan Zulay Kilicaslan, Saim OzkarAbstract:Abstract Herein we report the results of a detailed study on the in-situ generation of poly(N-vinyl-2-pyrrolidone) (PVP) stabilized nickel(0) nanoparticles and their catalytic activity in methanolysis of hydrazine Borane and ammonia Borane. PVP-stabilized nickel(0) nanoparticles with an average particle size of 3.0 ± 0.7 nm were in-situ generated from the reduction of nickel(II) 2-ethylhexanoate during the methanolysis of hydrazine Borane in the presence of PVP at room temperature. Polymer stabilized nickel(0) nanoparticles could be isolated from the solution by centrifugation and characterized by UV–vis spectroscopy, XPS, TEM, and SAED. PVP-stabilized nickel(0) nanoparticles are highly active and long lived catalyst in hydrogen generation from the methanolysis of hydrazine Borane and ammonia Borane at ambient temperature. The results of kinetic study reveal that the methanolysis is first order with respect to catalyst concentration and zero order regarding to substrate concentration in both cases. PVP-stabilized nickel(0) nanoparticles provide 14,500 turnovers in hydrogen generation from the methanolysis of hydrazine Borane and 5300 turnovers from the methanolysis of ammonia Borane. They also provide an initial turnover frequency of 35.6 and 12.1 min−1 for the catalytic methanolysis of hydrazine Borane and ammonia Borane, respectively.
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hydroxyapatite supported ruthenium 0 nanoparticles catalyst in hydrolytic dehydrogenation of ammonia Borane insight to the nanoparticles formation and hydrogen evolution kinetics
Applied Catalysis B-environmental, 2013Co-Authors: Serdar Akbayrak, Pelin Erdek, Saim OzkarAbstract:Abstract When a solution of ammonia Borane is added to the suspension of ruthenium(III) ions supported on hydroxyapatite, both reduction of ruthenium(III) to ruthenium(0) nanoparticles and hydrogen release from the hydrolysis of ammonia Borane occur concomitantly at room temperature. Using the hydrogen evolution from the hydrolysis of ammonia Borane as reporter reaction provides valuable insights to the formation kinetics of ruthenium(0) nanoparticles. Thus, the rate constants for the slow nucleation and autocatalytic surface growth of ruthenium(0) nanoparticles could be obtained. Furthermore, the evaluation of rate constants at various temperatures provides the estimation of activation energies for both reactions; Ea = 166 ± 7 kJ/mol for the nucleation and Ea = 59 ± 2 kJ/mol for the autocatalytic surface growth of ruthenium(0) nanoparticles. The ruthenium(0) nanoparticles, in situ formed during the hydrolysis of ammonia Borane and supported on hydroxyapatite, could be isolated from the reaction solution and characterized by a combination of advanced analytical techniques. The results show that (i) highly dispersed ruthenium(0) nanoparticles of 4.7 ± 0.7 nm size were formed on the surface of hydroxyapatite, (ii) they are highly active catalyst in the hydrolytic dehydrogenation of ammonia Borane with a turnover frequency value of 137 min−1 at 25.0 ± 0.1 °C, and (iii) they are long lived and reusable catalyst providing 87,000 turnovers for hydrogen generation from the hydrolysis of ammonia Borane and preserving 92% of their initial catalytic activity even after the fifth run of hydrolysis of ammonia Borane at 25.0 ± 0.1 °C. The results of kinetic study on the hydrogen generation from the hydrolysis of ammonia Borane were also reported including the activation energy of 58 ± 2 kJ/mol for the hydrolytic dehydrogenation of ammonia Borane.
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catalytic hydrolysis of hydrazine Borane for chemical hydrogen storage highly efficient and fast hydrogen generation system at room temperature
International Journal of Hydrogen Energy, 2011Co-Authors: Senem Karahan, Mehmet Zahmakiran, Saim OzkarAbstract:Abstract There has been rapidly growing interest for materials suitable to store hydrogen in solid state for transportation of hydrogen that requires materials with high volumetric and gravimetric storage capacity. B-N compounds such as ammonia-triBorane, ammonia-Borane and amine-Borane adducts are well suited for this purpose due to their light weight, high gravimetric hydrogen storage capacity and inclination for bearing protic (N-H) and hydridic (B-H) hydrogens. In addition to them, more recent study [26] has showed that hydrazine Borane with a gravimetric hydrogen storage capacity of 15.4% wt needs to be considered as another B-N compound that can be used for the storage of hydrogen. Herein we report for the first time, metal catalyzed hydrolysis of hydrazine Borane (N 2 H 4 BH 3 , HB) under air at room temperature. Among the catalyst systems tested, rhodium(III) chloride was found to provide the highest catalytic activity in this reaction. In the presence of rhodium(III) chloride, the aqueous solution of hydrazine Borane undergoes fast hydrolysis to release nearly 3.0 equivalent of H 2 at room temperature with previously unprecedented H 2 generation rate TOF = 12000 h −1 . More importantly, it was found that in the catalytic hydrolysis of hydrazine Borane the reaction between hydrazine Borane and water proceeds almost in stoichiometric proportion indicating that the efficient hydrogen generation can be achieved even from the highly concentrated solution of hydrazine Borane or in the solid state when water added to the solid hydrazine Borane. This finding is crucial especially for on-board application of the existing system. The work reported here also includes ( i ) finding the solubility of hydrazine Borane plus its stability against self-hydrolysis in water, ( ii ) the definition of reaction stoichiometry and the identification of reaction products for the catalytic hydrolysis of hydrazine Borane, ( iii ) the collection of wealthy kinetic data to demonstrate the effect of substrate and catalyst concentrations on the hydrogen generation rate and to determine the rate law for the catalytic hydrolysis of hydrazine Borane, ( iv ) the investigation of the effect of temperature on the rate of hydrogen generation and determination of activation parameters ( E a , ΔH # , and ΔS # ) for the catalytic hydrolysis of hydrazine Borane.
Max F. Rothschild - One of the best experts on this subject based on the ideXlab platform.
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determination of genetic structure and signatures of selection in three strains of tanzania shorthorn zebu Boran and friesian cattle by genome wide snp analyses
PLOS ONE, 2017Co-Authors: George Msalya, Eui-soo Kim, Emmanuel L. K. Laisser, Maulilio J. Kipanyula, Esron D. Karimuribo, Lughano J. M. Kusiluka, Sebastian W. Chenyambuga, Max F. RothschildAbstract:Background More than 90 percent of cattle in Tanzania belong to the indigenous Tanzania Short Horn Zebu (TSZ) population which has been classified into 12 strains based on historical evidence, morphological characteristics, and geographic distribution. However, specific genetic information of each TSZ population has been lacking and has caused difficulties in designing programs such as selection, crossbreeding, breed improvement or conservation. This study was designed to evaluate the genetic structure, assess genetic relationships, and to identify signatures of selection among cattle of Tanzania with the main goal of understanding genetic relationship, variation and uniqueness among them. Methodology/Principal findings The Illumina Bos indicus SNP 80K BeadChip was used to genotype genome wide SNPs in 168 DNA samples obtained from three strains of TSZ cattle namely Maasai, Tarime and Sukuma as well as two comparative breeds; Boran and Friesian. Population structure and signatures of selection were examined using principal component analysis (PCA), admixture analysis, pairwise distances (FST), integrated haplotype score (iHS), identical by state (IBS) and runs of homozygosity (ROH). There was a low level of inbreeding (F~0.01) in the TSZ population compared to the Boran and Friesian breeds. The analyses of FST, IBS and admixture identified no considerable differentiation between TSZ trains. Importantly, common ancestry in Boran and TSZ were revealed based on admixture and IBD, implying gene flow between two populations. In addition, Friesian ancestry was found in Boran. A few common significant iHS were detected, which may reflect influence of recent selection in each breed or strain. Conclusions Population admixture and selection signatures could be applied to develop conservation plan of TSZ cattle as well as future breeding programs in East African cattle.
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Signatures of selection in Tanzanian shorthorn Zebu cattle and Boran breed.
2017Co-Authors: George Msalya, Eui-soo Kim, Emmanuel L. K. Laisser, Maulilio J. Kipanyula, Esron D. Karimuribo, Lughano J. M. Kusiluka, Sebastian W. Chenyambuga, Max F. RothschildAbstract:Signatures of selection in Tanzanian shorthorn Zebu cattle and Boran breed.
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Signatures of selection (iHS) in the Tanzanian TSZ cattle population and two breeds.
2017Co-Authors: George Msalya, Eui-soo Kim, Emmanuel L. K. Laisser, Maulilio J. Kipanyula, Esron D. Karimuribo, Lughano J. M. Kusiluka, Sebastian W. Chenyambuga, Max F. RothschildAbstract:A: Sukuma B. Tarime C. Maasai D. Boran E. Friesian.
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Photographs of individuals representing the Tanzania cattle populations and breeds involved in the present study.
2017Co-Authors: George Msalya, Eui-soo Kim, Emmanuel L. K. Laisser, Maulilio J. Kipanyula, Esron D. Karimuribo, Lughano J. M. Kusiluka, Sebastian W. Chenyambuga, Max F. RothschildAbstract:A: Sukuma B. Tarime C. Maasai D. Boran E. Friesian (Photo by ELKL).
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Principal components analysis between individuals of Tanzanian cattle.
2017Co-Authors: George Msalya, Eui-soo Kim, Emmanuel L. K. Laisser, Maulilio J. Kipanyula, Esron D. Karimuribo, Lughano J. M. Kusiluka, Sebastian W. Chenyambuga, Max F. RothschildAbstract:Sukuma (red), Tarime (yellow), Maasai (green), Boran (blue) and Friesian (purple) are indicated in different colors.
Stephen J Kemp - One of the best experts on this subject based on the ideXlab platform.
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cytokine mrna profiling of peripheral blood mononuclear cells from trypanotolerant and trypanosusceptible cattle infected with trypanosoma congolense
Physiological Genomics, 2006Co-Authors: Grace M Ogorman, Jan Naessens, Olivier Hanotte, Morris Agaba, J P Gibson, Stephen D E Park, Emmeline W Hill, Kieran G Meade, Laura C Mitchell, Stephen J KempAbstract:To examine differences in cytokine profiles that may confer tolerance/susceptibility to bovine African trypanosomiasis, N'Dama (trypanotolerant, n = 8) and Boran (trypanosusceptible, n = 8) cattle ...
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mapping of quantitative trait loci controlling trypanotolerance in a cross of tolerant west african n dama and susceptible east african Boran cattle
Proceedings of the National Academy of Sciences of the United States of America, 2003Co-Authors: Olivier Hanotte, Stephen J Kemp, Y I Ronin, Morris Agaba, P Nilsson, A Gelhaus, Rolf D Horstmann, Y Sugimoto, J P Gibson, Abraham B KorolAbstract:Trypanosomosis, or sleeping sickness, is a major disease constraint on livestock productivity in sub-Saharan Africa. To identify quantitative trait loci (QTL) controlling resistance to trypanosomosis in cattle, an experimental cross was made between trypanotolerant African N'Dama (Bos taurus) and trypanosusceptible improved Kenya Boran (Bos indicus) cattle. Sixteen phenotypic traits were defined describing anemia, body weight, and parasitemia. One hundred seventy-seven F2 animals and their parents and grandparents were genotyped at 477 molecular marker loci covering all 29 cattle autosomes. Total genome coverage was 82%. Putative QTL were mapped to 18 autosomes at a genomewise false discovery rate of <0.20. The results are consistent with a single QTL on 17 chromosomes and two QTL on BTA16. Individual QTL effects ranged from approximately 6% to 20% of the phenotypic variance of the trait. Excluding chromosomes with ambiguous or nontrypanotolerance effects, the allele for resistance to trypanosomosis originated from the N'Dama parent at nine QTL and from the Kenya Boran at five QTL, and at four QTL there is evidence of an overdominant mode of inheritance. These results suggest that selection for trypanotolerance within an F2 cross between N'Dama and Boran cattle could produce a synthetic breed with higher trypanotolerance levels than currently exist in the parental breeds.
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responses of bovine chimaeras combining trypanosomosis resistant and susceptible genotypes to experimental infection with trypanosoma congolense
Veterinary Parasitology, 2003Co-Authors: Jan Naessens, Stephen G A Leak, David Kennedy, Stephen J Kemp, A J TealeAbstract:West African N'Dama cattle have developed a genetic capacity to survive, reproduce and remain productive under trypanosomosis risk. The cellular and molecular bases of this so-called trypanotolerance are not known, but the trait is manifested by the N'Dama's greater capacity to control parasitaemia and anaemia development during an infection. In order to examine the role of the haematopoietic system in trypanotolerance, we have exploited the tendency for the placentas of bovine twin embryos to fuse. Placental fusion in cattle results in bone marrow chimaerism in twins. By comparison with the N'Dama, cattle of the East African Boran breed are relatively susceptible. We evaluated the role of the haemopoietic system in trypanotolerance by comparing the performance of five Chimaeric Boran/N'Dama twin calves with that of singletons of the two breeds. Chimaeric Boran/N'Dama pairs of twins were produced in recipient Boran cows by embryo transfer, and the majority of haemopoietic cells in all twinned individuals were of Boran origin. Thus, N'Dama chimaeras differed from N'Dama singletons in that the bulk of their haemopoietic system was derived from their susceptible Boran twins, while Boran chimaeras differed little from Boran control animals. All cattle became parasitaemic and developed anaemia. The N'Dama chimaeras did not manage their anaemia and white blood cell counts effectively. However, they were able to limit parasitaemia development. These results suggest that trypanotolerance is the result of two mechanisms, one that improves parasite control and is independent of the genetic origin of the haemopoietic tissue, and another that is influenced by haemopoietic tissue genotype and which improves control over anaemia. The capacity to maintain growth during infection was similarly dependent on the genetic origin of the haemopoietic tissue.
Dennis P Curran - One of the best experts on this subject based on the ideXlab platform.
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insertion of reactive rhodium carbenes into boron hydrogen bonds of stable n heterocyclic carbene Boranes
ChemInform, 2014Co-Authors: Dennis P CurranAbstract:This method also works with substituted imidazole-Borane adducts as well as 1,2,4-triazole-derived Borane adducts.
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radical reductions of alkyl halides bearing electron withdrawing groups with n heterocyclic carbene Boranes
Organic and Biomolecular Chemistry, 2011Co-Authors: Shau-hua Ueng, Louis Fensterbank, Emmanuel Lacote, Max Malacria, Dennis P CurranAbstract:1,3-Dimethylimidazol-2-ylidene Borane and 2,4-dimethyl-1,2,4-triazol-3-ylidene Borane are found to be useful reagents for the reduction of alkyl iodides and bromides bearing nearby electron withdrawing substituents. Signatures of radical chain reactions are seen in many cases, but ionic reductions may also be occurring with some substrates. The reagents are attractive because of their low molecular weight, their availability from inexpensive precursors, and their stability. Separation of the Borane products from the target products is readily accomplished either with or without prior regeneration of the Borane for later reuse. 2,4-Dimethyl-1,2,4-triazol-3-ylidene Borane is versatile because both starting Borane and its derived products can be removed by extraction with water.
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complexes of Borane and n heterocyclic carbenes a new class of radical hydrogen atom donor
Journal of the American Chemical Society, 2008Co-Authors: Shau-hua Ueng, Malika Makhlouf Brahmi, Etienne Derat, Louis Fensterbank, Emmanuel Lacote, Max Malacria, Dennis P CurranAbstract:Calculations suggest that complexes of Borane with N-heterocyclic carbenes (NHC) have B−H bond dissocation energies more then 20 kcal/mol less than free Borane, diBorane, Borane−THF, and related complexes. Values are in the range of popular radical hydrogen atom donors like tin hydrides (70−80 kcal/mol). The resulting prediction that NHC Borane complexes could be used as radical hydrogen atom donors was verified by radical deoxygenations of xanthates by using either AIBN or triethylBorane as initiator.