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Jairton Dupont - One of the best experts on this subject based on the ideXlab platform.
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Synthesis and Enzymatic Evaluation of the Guanosine Analogue 2-Amino-6-mercapto- 7-methylpurine Ribonucleoside (MESG). Insights into the Phosphorolysis Reaction Mechanism based on the Blueprint Transition State: SN1 or SN2?
2014Co-Authors: Silvia M. Tamborim, Luiz C A. Basso, Diógenes E S. Santose, Jairton DupontAbstract:A modificação experimental para a síntese do MESG (2-amino-6-mercapto-7-metilpurina ribonucleosídeo) 1 foi realizada com sucesso e sua caracterização total apresentada. ESI(+)-MSMS em alta resolução foram realizados indicando que a clivagem nucleosídica como principal e um possível mecanismo SN1. Cálculos ab initio baseados em estados de transição blueprint corroboram com a proposta de um mecanismo SN1 e descartam a possibilidade de um mecanismo SN2. Ensaios com a enzima purina nucleosídica fosforilase (PNP, tanto humana como de M. tuberculosis) indicam a eficiência do substrato na reação de fosforilação do MESG e permitem a determinação de fosfato inorgânico em tempo real em ensaios biológicos. A modified experimental procedure for the synthesis of MESG (2-amino-6-mercapto-7-methylpurine ribonucleoside) 1 has been successfully performed and its full characterization is presented. High resolution ESI(+)-MSMS indicates both the nucleoside bond cleavage as the main fragmentation in the gas phase and a possible SN1 Mechanism. Ab initio transition state calculations based on the blue print transition state support this mechanistic rationale and discard an alternative SN2 Mechanism. Assays using purine nucleoside phosphorylase (PNP) enzyme (human and M. tuberculosis sources) indicate its efficiency in the phosphorolysis of MESG an
Dupont Jairton - One of the best experts on this subject based on the ideXlab platform.
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Synthesis and enzymatic evaluation of the guanosine analogue 2-amino-6-mercapto-7-methylpurine ribonucleoside (MESG). Insights into the phosphorolysis reaction Mechanism based on the blueprint transition state: SN1 or sn2
2010Co-Authors: Brenno Amaro Da ,silveira Neto, Lápis, Alexandre Augusto Moreira, Netz, Paulo Augusto, Spencer John, Dias, Silvio Luis Pereira, Tamborim Takeuchi, Silvia Margonei Mesquita, Basso, Luiz Augusto, Santos, Diogenes Santiago, Dupont JairtonAbstract:A modificação experimental para a síntese do MESG (2-amino-6-mercapto-7-metilpurina ribonucleosídeo) 1 foi realizada com sucesso e sua caracterização total apresentada. ESI(+)-MSMS em alta resolução foram realizados indicando que a clivagem nucleosídica como principal e um possível mecanismo SN1. Cálculos ab initio baseados em estados de transição blueprint corroboram com a proposta de um mecanismo SN1 e descartam a possibilidade de um mecanismo SN2. Ensaios com a enzima purina nucleosídica fosforilase (PNP, tanto humana como de M. tuberculosis) indicam a eficiência do substrato na reação de fosforilação do MESG e permitem a determinação de fosfato inorgânico em tempo real em ensaios biológicos.A modified experimental procedure for the synthesis of MESG (2-amino-6-mercapto-7-methylpurine ribonucleoside) 1 has been successfully performed and its full characterization is presented. High resolution ESI(+)-MSMS indicates both the nucleoside bond cleavage as the main fragmentation in the gas phase and a possible SN1 Mechanism. Ab initio transition state calculations based on the blue print transition state support this mechanistic rationale and discard an alternative SN2 Mechanism. Assays using purine nucleoside phosphorylase (PNP) enzyme (human and M. tuberculosis sources) indicate its efficiency in the phosphorolysis of MESG and allow the quantitative determination of inorganic phosphate in real time assay
Jesper Z. Haeggström - One of the best experts on this subject based on the ideXlab platform.
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Mutation of tyrosine 383 in leukotriene A4 hydrolase allows conversion of leukotriene A4 into 5S,6S-dihydroxy-7,9-trans-11,14-cis-eicosatetraenoic acid. Implications for the epoxide hydrolase Mechanism.
Journal of Biological Chemistry, 1997Co-Authors: Martina Andberg, Mats Hamberg, Jesper Z. HaeggströmAbstract:Abstract Leukotriene A4 hydrolase is a bifunctional zinc metalloenzyme that catalyzes the final step in the biosynthesis of the proinflammatory mediator leukotriene B4. In previous studies with site-directed mutagenesis on mouse leukotriene A4 hydrolase, we have identified Tyr-383 as a catalytic amino acid involved in the peptidase reaction. Further characterization of the mutants in position 383 revealed that [Y383H], [Y383F], and [Y383Q] leukotriene A4hydrolases catalyzed hydrolysis of leukotriene A4 into a novel enzymatic metabolite. From analysis by high performance liquid chromatography, gas chromatography/mass spectrometry of material generated in the presence of H2 16O or H2 18O, steric analysis of the hydroxyl groups, treatment with soybean lipoxygenase, and comparison with a synthetic standard, the novel metabolite was assigned the structure 5S,6S-dihydroxy-7,9-trans-11,14-cis-eicosatetraenoic acid (5S,6S-DHETE). The kinetic parameters for the formation of 5S,6S-DHETE and leukotriene B4 were found to be similar. Also, both activities were susceptible to suicide inactivation and were equally sensitive to inhibition by bestatin. Moreover, from the stereochemical configuration of the vicinal diol, it could be inferred that 5S,6S-DHETE is formed via an SN1 Mechanism involving a carbocation intermediate, which in turn indicates that enzymatic hydrolysis of leukotriene A4 into leukotriene B4 follows the same Mechanism. Inasmuch as soluble epoxide hydrolase utilizes leukotriene A4 as substrate to produce 5S,6R-DHETE, our results also suggest a functional relationship between leukotriene A4 hydrolase and xenobiotic epoxide hydrolases.
Shu Kobayashi - One of the best experts on this subject based on the ideXlab platform.
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lewis acid mediated acetal substitution reactions Mechanism and application to asymmetric catalysis
Advanced Synthesis & Catalysis, 2011Co-Authors: Shu Kobayashi, Kenzo Arai, Takeshi Yamakawa, Yijing Chen, Matthew M Salter, Yasuhiro YamashitaAbstract:Substitution reactions of acetals with carbon nucleophiles are fundamental and conventional organic reactions. We succeeded in the preparation of an optically active acetal, which reacted with a silyl enol ether smoothly to afford the desired adducts in racemic forms. By comparison of the ees of the products with the ees of the recovered acetals, we concluded that the aldol-type reactions proceeded not via direct displacement (SN2) or contact ion pairs (intimate ion pair) (SN1) but by a free oxocarbenium ion (SN1) Mechanism. Next, a study to achieve asymmetric catalysis of the acetal substitution reactions was conducted. After many trials, it was found that a chiral niobium complex prepared from pentamethoxyniobium [Nb(OMe)5] and a tetradentate BINOL derivative could achieve high enantioselectivities. Asymmetric aldol-type reactions of acetals with silyl enol ethers proceeded smoothly to afford the corresponding aldol-type adducts in good yields with high enantioselectivities.
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unusual carbon carbon bond formations between allylboronates and acetals or ketals catalyzed by a peculiar indium i lewis acid
Organic Letters, 2010Co-Authors: Uwe Schneider, Hai T Dao, Shu KobayashiAbstract:InIOTf has been uncovered as an effective Lewis acid catalyst for unprecedented nucleophilic substitution of acetals or ketals with allylboronates. A transmetalative SN1 Mechanism is proposed in which a single InI center acts as a dual catalyst to activate both reagents sequentially. Contrary to the classic γ-selectivity of allylsilanes (Hosomi−Sakurai reaction), this InI-catalyzed borono variant displays distinct α-selectivity. Substrate scope and functional group tolerance proved to be excellent.
Silvia M. Tamborim - One of the best experts on this subject based on the ideXlab platform.
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Synthesis and Enzymatic Evaluation of the Guanosine Analogue 2-Amino-6-mercapto- 7-methylpurine Ribonucleoside (MESG). Insights into the Phosphorolysis Reaction Mechanism based on the Blueprint Transition State: SN1 or SN2?
2014Co-Authors: Silvia M. Tamborim, Luiz C A. Basso, Diógenes E S. Santose, Jairton DupontAbstract:A modificação experimental para a síntese do MESG (2-amino-6-mercapto-7-metilpurina ribonucleosídeo) 1 foi realizada com sucesso e sua caracterização total apresentada. ESI(+)-MSMS em alta resolução foram realizados indicando que a clivagem nucleosídica como principal e um possível mecanismo SN1. Cálculos ab initio baseados em estados de transição blueprint corroboram com a proposta de um mecanismo SN1 e descartam a possibilidade de um mecanismo SN2. Ensaios com a enzima purina nucleosídica fosforilase (PNP, tanto humana como de M. tuberculosis) indicam a eficiência do substrato na reação de fosforilação do MESG e permitem a determinação de fosfato inorgânico em tempo real em ensaios biológicos. A modified experimental procedure for the synthesis of MESG (2-amino-6-mercapto-7-methylpurine ribonucleoside) 1 has been successfully performed and its full characterization is presented. High resolution ESI(+)-MSMS indicates both the nucleoside bond cleavage as the main fragmentation in the gas phase and a possible SN1 Mechanism. Ab initio transition state calculations based on the blue print transition state support this mechanistic rationale and discard an alternative SN2 Mechanism. Assays using purine nucleoside phosphorylase (PNP) enzyme (human and M. tuberculosis sources) indicate its efficiency in the phosphorolysis of MESG an