GSTDTAP

浏览/检索结果: 共9条,第1-9条 帮助

已选(0)清除 条数/页:   排序方式:
Focus on the role of forests and soils in meeting climate change mitigation goals: summary 期刊论文
ENVIRONMENTAL RESEARCH LETTERS, 2020, 15 (4)
作者:  Moomaw, William R.;  Law, Beverly E.;  Goetz, Scott J.
收藏  |  浏览/下载:33/0  |  提交时间:2020/07/02
natural climate solutions  forest and soil carbon  tropical forests  carbon sequestration  forest products carbon storage  forest carbon accounting  forest bioenergy accounting  
A general carbonyl alkylative amination for tertiary amine synthesis 期刊论文
NATURE, 2020
作者:  Ouyang, David;  He, Bryan;  Ghorbani, Amirata;  Yuan, Neal;  Ebinger, Joseph;  Langlotz, Curtis P.;  Heidenreich, Paul A.;  Harrington, Robert A.;  Liang, David H.;  Ashley, Euan A.;  Zou, James Y.
收藏  |  浏览/下载:26/0  |  提交时间:2020/07/03

The ubiquity of tertiary alkylamines in pharmaceutical and agrochemical agents, natural products and small-molecule biological probes(1,2) has stimulated efforts towards their streamlined synthesis(3-9). Arguably the most robust method for the synthesis of tertiary alkylamines is carbonyl reductive amination(3), which comprises two elementary steps: the condensation of a secondary alkylamine with an aliphatic aldehyde to form an all-alkyl-iminium ion, which is subsequently reduced by a hydride reagent. Direct strategies have been sought for a '  higher order'  variant of this reaction via the coupling of an alkyl fragment with an alkyl-iminium ion that is generated in situ(10-14). However, despite extensive efforts, the successful realization of a '  carbonyl alkylative amination'  has not yet been achieved. Here we present a practical and general synthesis of tertiary alkylamines through the addition of alkyl radicals to all-alkyl-iminium ions. The process is facilitated by visible light and a silane reducing agent, which trigger a distinct radical initiation step to establish a chain process. This operationally straightforward, metal-free and modular transformation forms tertiary amines, without structural constraint, via the coupling of aldehydes and secondary amines with alkyl halides. The structural and functional diversity of these readily available precursors provides a versatile and flexible strategy for the streamlined synthesis of complex tertiary amines.


The synthesis of tertiary amines is achieved through a carbonyl alkylative amination reaction facilitated by visible light, in which an aldehyde and an amine condense to form an iminium ion that subsequently reacts with alkyl radical.


  
Late-stage oxidative C(sp(3))-H methylation 期刊论文
NATURE, 2020, 580 (7805) : 621-+
作者:  Fessler, Evelyn;  Eckl, Eva-Maria;  Schmitt, Sabine;  Mancilla, Igor Alves;  Meyer-Bender, Matthias F.;  Hanf, Monika;  Philippou-Massier, Julia;  Krebs, Stefan;  Zischka, Hans;  Jae, Lucas T.
收藏  |  浏览/下载:71/0  |  提交时间:2020/07/03

Frequently referred to as the '  magic methyl effect'  , the installation of methyl groups-especially adjacent (alpha) to heteroatoms-has been shown to dramatically increase the potency of biologically active molecules(1-3). However, existing methylation methods show limited scope and have not been demonstrated in complex settings(1). Here we report a regioselective and chemoselective oxidative C(sp(3))-H methylation method that is compatible with late-stage functionalization of drug scaffolds and natural products. This combines a highly site-selective and chemoselective C-H hydroxylation with a mild, functional-group-tolerant methylation. Using a small-molecule manganese catalyst, Mn(CF3PDP), at low loading (at a substrate/catalyst ratio of 200) affords targeted C-H hydroxylation on heterocyclic cores, while preserving electron-neutral and electron-rich aryls. Fluorine- or Lewis-acid-assisted formation of reactive iminium or oxonium intermediates enables the use of a mildly nucleophilic organoaluminium methylating reagent that preserves other electrophilic functionalities on the substrate. We show this late-stage C(sp(3))-H methylation on 41 substrates housing 16 different medicinally important cores that include electron-rich aryls, heterocycles, carbonyls and amines. Eighteen pharmacologically relevant molecules with competing sites-including drugs (for example, tedizolid) and natural products-are methylated site-selectively at the most electron rich, least sterically hindered position. We demonstrate the syntheses of two magic methyl substrates-an inverse agonist for the nuclear receptor RORc and an antagonist of the sphingosine-1-phosphate receptor-1-via late-stage methylation from the drug or its advanced precursor. We also show a remote methylation of the B-ring carbocycle of an abiraterone analogue. The ability to methylate such complex molecules at late stages will reduce synthetic effort and thereby expedite broader exploration of the magic methyl effect in pursuit of new small-molecule therapeutics and chemical probes.


A manganese-catalysed oxidative C(sp(3))-H methylation method allows a methyl group to be selectively installed into medicinally important heterocycles, providing a way to improve pharmaceuticals and better understand the '  magic methyl effect'  .


  
Synthesis of rare sugar isomers through site-selective epimerization 期刊论文
NATURE, 2020: 403-+
作者:  Jackson, Hartland W.;  Fischer, Jana R.;  Zanotelli, Vito R. T.;  Ali, H. Raza;  Mechera, Robert;  Soysal, Savas D.;  Moch, Holger;  Muenst, Simone;  Varga, Zsuzsanna;  Weber, Walter P.;  Bodenmiller, Bernd
收藏  |  浏览/下载:24/0  |  提交时间:2020/07/03

Glycans have diverse physiological functions, ranging from energy storage and structural integrity to cell signalling and the regulation of intracellular processes(1). Although biomass-derived carbohydrates (such as d-glucose, d-xylose and d-galactose) are extracted on commercial scales, and serve as renewable chemical feedstocks and building blocks(2,3), there are hundreds of distinct monosaccharides that typically cannot be isolated from their natural sources and must instead be prepared through multistep chemical or enzymatic syntheses(4,5). These '  rare'  sugars feature prominently in bioactive natural products and pharmaceuticals, including antiviral, antibacterial, anticancer and cardiac drugs(6,7). Here we report the preparation of rare sugar isomers directly from biomass carbohydrates through site-selective epimerization reactions. Mechanistic studies establish that these reactions proceed under kinetic control, through sequential steps of hydrogen-atom abstraction and hydrogen-atom donation mediated by two distinct catalysts. This synthetic strategy provides concise and potentially extensive access to this valuable class of natural compounds.


Various rare sugars that cannot be isolated from natural sources are synthesized using light-driven epimerization, a process which may find application in other synthetic scenarios.


  
Synthesis of arborane triterpenols by a bacterial oxidosqualene cyclase 期刊论文
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 2017, 114 (2) : 245-250
作者:  Banta, Amy B.;  Wei, Jeremy H.;  Gill, Clare C. C.;  Giner, Jose-Luis;  Welander, Paula V.
收藏  |  浏览/下载:16/0  |  提交时间:2019/11/27
triterpene synthase  isoarborinol  sterol  biomarker  natural products  
Evaluation of the combined toxicity assessment and cumulative risk assessment of ecologically relevant mixtures of plant protection Products (PPPs) under Norwegian conditions 科技报告
来源:Center for International Climate and Environmental Research-Oslo (CICERO). 出版年: 2016
作者:  Tollefsen, Knut Erik;  Bæk, Kine;  Almeida, Ana;  Haug, Linn Anette;  Norli, Hans;  Odenmarck, Sven;  Stenrød, Marianne
收藏  |  浏览/下载:9/0  |  提交时间:2019/04/05
VDP::Matematikk og naturvitenskap: 400  VDP::Mathematics and natural scienses: 400  Kombinerte effekter / Combined effects  Kumulativ risikovurdering / Cumulative risk assessment  Plantevernmidler / Plant protection products  Regulatorisk godkjenning / Regulatory approval  
Exposure and toxicity of mixtures of plant protection products (PPPs) in the environment under Norwegian conditions. Evaluation of a cumulative environmental risk assessment of PPPs 科技报告
来源:Center for International Climate and Environmental Research-Oslo (CICERO). 出版年: 2015
作者:  Petersen, Karina;  Stenrød, Marianne;  Odenmarck, Sven Roar;  Fredriksen, Lene;  Gomes, Tania;  Backhaus, Thomas;  Tollefsen, Knut-Erik
收藏  |  浏览/下载:16/0  |  提交时间:2019/04/05
VDP::Matematikk og naturvitenskap: 400  VDP::Mathematics and natural scienses: 400  Kombinerte effekter / Combined effects  Kummulativ risikovurdering / Cumulative risk assessment  Plantevernmidler / Plant protection products  Risikoreduserende tiltak / Mitigation measures  
LABORATORY REPORT ON IODINE ({sup 129}I AND {sup 127}I) SPECIATION, TRANSFORMATION AND MOBILITY IN HANFORD GROUNDWATER, SUSPENDED PARTICLES AND SEDIMENTS 科技报告
来源:US Department of Energy (DOE). 出版年: 2012
作者:  Kaplan, D.;  Santschi, P.;  Xu, C.;  Zhang, S.;  Ho, Y.;  Li, H.;  Schwehr, K.
收藏  |  浏览/下载:23/0  |  提交时间:2019/04/05
Iodide  Iodate  Organo-Iodine  Fission Products  Natural Organic Matter  
Biogeochemical Considerations Related To The Remediation Of I-129 Plumes 科技报告
来源:US Department of Energy (DOE). 出版年: 2012
作者:  Kaplan, D. I. [Savannah River Site (SRS), Aiken, SC (United States)];  Yeager, C. [Los Alamos National Laboratory , Los Alamos, NM (United States)];  Denham, M. E. [Savannah River Site (SRS), Aiken, SC (United States)];  Zhang, S. [Texas A&;  M University, Galveston, TX (United States)];  Xu, C. [Texas A&;  M University, Galveston, TX (United States)];  Schwehr, K. A. [Texas A&;  M University, Galveston, TX (United States)];  Li, H. P. [Texas A&;  M University, Galveston, TX (United States)];  Brinkmeyer, R. [Texas A&;  M University, Galveston, TX (United States)];  Santschi, P. H. [Texas A&;  M University, Galveston, TX (United States)]
收藏  |  浏览/下载:19/0  |  提交时间:2019/04/05
Iodide  Iodate  Organo-Iodine  Fission Products  Natural Organic Matter