RESUMO
Dirhodium caprolactamate, Rh(2)(cap)(4), is a very efficient catalyst for the generation of the tert-butylperoxy radical from tert-butyl hydroperoxide, and the tert-butylperoxy radical is a highly effective oxidant for phenols and anilines. These reactions are performed with 70% aqueous tert-butyl hydroperoxide using dirhodium caprolactamate in amounts as low as 0.01 mol % to oxidize para-substituted phenols to 4-(tert-butyldioxy)cyclohexadienones. Although these transformations have normally been performed in halocarbon solvents, there is a significant rate enhancement when Rh(2)(cap)(4)-catalyzed phenol oxidations are performed in toluene or chlorobenzene. Electron-rich and electron-poor phenolic substrates undergo selective oxidation in good to excellent yields, but steric influences from bulky para substituents force oxidation onto the ortho position resulting in ortho-quinones. Comparative results with RuCl(2)(PPh(3))(3) and CuI are provided, and mechanistic comparisons are made between these catalysts that are based on diastereoselectivity (reactions with estrone), regioselectivity (reactions with p-tert-butylphenol), and chemoselectivity in the formation of 4-(tert-butyldioxy)cyclohexadienones. The data obtained are consistent with hydrogen atom abstraction by the tert-butylperoxy radical followed by radical combination between the phenoxy radical and the tert-butylperoxy radical. Under similar reaction conditions, para-substituted anilines are oxidized to nitroarenes in good yield, presumably through the corresponding nitrosoarene, and primary amines are oxidized to carbonyl compounds by TBHP in the presence of catalytic amounts of Rh(2)(cap)(4).
Assuntos
Compostos de Anilina/química , Cicloexenos/síntese química , Oxidantes/química , Fenóis/química , terc-Butil Hidroperóxido/química , Aminas/química , Catálise , Elétrons , Estrona/química , Oxirredução , Oxigênio , Prótons , Ródio/química , Solventes/química , Estereoisomerismo , Especificidade por Substrato , ÁguaRESUMO
The Canadian Society for Exercise Physiology assembled a Consensus Panel representing national organizations, content experts, methodologists, stakeholders, and end-users and followed an established guideline development procedure to create the Canadian 24-Hour Movement Guidelines for Adults aged 18-64 years and Adults aged 65 years or older: An Integration of Physical Activity, Sedentary Behaviour, and Sleep. These guidelines underscore the importance of movement behaviours across the whole 24-h day. The development process followed the strategy outlined in the Appraisal of Guidelines for Research and Evaluation (AGREE) II instrument. A large body of evidence was used to inform the guidelines including 2 de novo systematic reviews and 4 overviews of reviews examining the relationships among movement behaviours (physical activity, sedentary behaviour, sleep, and all behaviours together) and several health outcomes. Draft guideline recommendations were discussed at a 4-day in-person Consensus Panel meeting. Feedback from stakeholders was obtained by survey (n = 877) and the draft guidelines were revised accordingly. The final guidelines provide evidence-based recommendations for a healthy day (24-h), comprising a combination of sleep, sedentary behaviours, and light-intensity and moderate-to-vigorous-intensity physical activity. Dissemination and implementation efforts with corresponding evaluation plans are in place to help ensure that guideline awareness and use are optimized. Novelty First ever 24-Hour Movement Guidelines for Adults aged 18-64 years and Adults aged 65 years or older with consideration of a balanced approach to physical activity, sedentary behaviour, and sleep Finalizes the suite of 24-Hour Movement Guidelines for Canadians across the lifespan.
Assuntos
Exercício Físico/fisiologia , Exercício Físico/psicologia , Comportamento Sedentário , Sono/fisiologia , Adolescente , Adulto , Idoso , Envelhecimento/fisiologia , Envelhecimento/psicologia , Canadá , Medicina Baseada em Evidências , Feminino , Comportamentos Relacionados com a Saúde , Humanos , Masculino , Pessoa de Meia-Idade , Movimento , Condicionamento Físico Humano , Participação dos Interessados , Adulto JovemRESUMO
Dirhodium(II) caprolactamate exhibits optimal efficiency for the production of the tert-butylperoxy radical, which is a selective reagent for hydrogen atom abstraction. These oxidation reactions occur with aqueous tert-butyl hydroperoxide (TBHP) without rapid hydrolysis of the caprolactamate ligands on dirhodium. Allylic oxidations of enones yield the corresponding enedione in moderate to high yields, and applications include allylic oxidations of steroidal enones. Although methylene oxidation to a ketone is more effective, methyl oxidation to a carboxylic acid can also be achieved. The superior efficiency of dirhodium(II) caprolactamate as a catalyst for allylic oxidations by TBHP (mol % of catalyst, % conversion) is described in comparative studies with other metal catalysts that are also reported to be effective for allylic oxidations. That different catalysts produce essentially the same mixture of products with the same relative yields suggests that the catalyst is not involved in product-forming steps. Mechanistic implications arising from studies of allylic oxidation with enones provide new insights into factors that control product formation. A previously undisclosed disproportionation pathway, catalyzed by the tert-butoxy radical, of mixed peroxides for the formation of ketone products via allylic oxidation has been uncovered.
Assuntos
Alcenos/química , Caprolactama/análogos & derivados , Compostos Organometálicos/química , Oxidantes/química , Água/química , terc-Butil Hidroperóxido/química , Caprolactama/química , Catálise , Cicloexenos/química , TemperaturaRESUMO
[Reaction: see text] Intramolecular photocycloaddition of 4 leads to the formation of cyclobutene photoadduct 5. Secondary photoreaction of 5 then affords either cyclobutane 19 or the bridged product 7, as a function of R (H or TMS).
Assuntos
Alcenos/química , Alcinos/química , Ciclobutanos/química , Dioxanos/química , Compostos Heterocíclicos com 3 Anéis/química , Ciclização , Estrutura Molecular , FotoquímicaRESUMO
The reaction of Na[RuCl4(SO(CH3)2)2], 1, with one equivalent of FcCONHCH2C6H4N (Fc=FeC10H9), L1, FcCOOCH2CH2C3H3N2, L2, FcCOOC6H4N, L3, afforded the dinuclear species, Na[FcCONHCH2C6H4N[RuCl4(SO(CH3)2)]], RuL1, Na[FcCOOCH2CH2C3H3N2[RuCl4(SO(CH3)2)]], RuL2, Na[FcCOOC6H4N(RuCl4(SO(CH3)2))], RuL3, respectively, yielding, in each case, a ferrocene moiety bridged to a ruthenium center. The complexes were characterized by NMR, IR, and XRD (X-ray diffraction). The sulfoxide ligands are bonded to the metal through the sulfur atom. The complexes were evaluated for their biological activity with pBluescript DNA plasmid, and the protein BSA (bovine serum albumin). These reactions were monitored by XAS (X-ray absorption spectroscopy), EXAFS (extended X-ray Absorption Fine Structure), NMR, UV/visible, emission spectroscopy, and gel electrophoresis. Donor atoms from the biomolecules substitute for the chloride ligands in the parent complexes.
Assuntos
DNA/química , Compostos Ferrosos/síntese química , Compostos de Rutênio/síntese química , Soroalbumina Bovina/química , Compostos Ferrosos/química , Metalocenos , Modelos Moleculares , Compostos de Rutênio/química , Solubilidade , Análise Espectral/métodos , Água/química , Difração de Raios XRESUMO
Ligand recognition in purine riboswitches is a complex process requiring different levels of conformational changes. Recent efforts in the area of purine riboswitch research have focused on ligand analogue binding studies. In the case of the guanine xanthine phosphoribosyl transferase (xpt) riboswitch, synthetic analogues that resemble guanine have the potential to tightly bind and subsequently influence the genetic expression of xpt mRNA in prokaryotes. We have carried out 25 ns Molecular Dynamics (MD) simulation studies of the aptamer domain of the xpt G-riboswitch in four different states: guanine riboswitch in free form, riboswitch bound with its cognate ligand guanine, and with two guanine analogues SJ1 and SJ2. Our work reveals novel interactions of SJ1 and SJ2 ligands with the binding core residues of the riboswitch. The ligands proposed in this work bind to the riboswitch with greater overall stability and lower root mean square deviations and fluctuations compared to guanine ligand. Reporter gene assay data demonstrate that the ligand analogues, upon binding to the RNA, lower the genetic expression of the guanine riboswitch. Our work has important implications for future ligand design and binding studies in the exciting field of riboswitches.
Assuntos
Guanina/análogos & derivados , Guanina/química , Pentosiltransferases/química , Riboswitch , Aptâmeros de Nucleotídeos/química , Sequência de Bases , Regulação Bacteriana da Expressão Gênica , Genes Reporter , Guanina/fisiologia , Ligação de Hidrogênio , Sequências Repetidas Invertidas , Simulação de Dinâmica Molecular , Conformação de Ácido Nucleico , Pentosiltransferases/genética , Termodinâmica , Ativação Transcricional , beta-Galactosidase/biossíntese , beta-Galactosidase/genéticaRESUMO
[reaction: see text] A synthesis of 28, the carbon framework of the eleutherobin aglycone, is reported in a 15-step sequence from readily available starting materials. The tandem Diels-Alder reaction of 6 and 7 to produce 18, in which three new rings and six new stereocenters are formed, is a key step in the reaction sequence.
Assuntos
Alcaloides/síntese química , Antineoplásicos/síntese química , Diterpenos , Antozoários/química , Ciclização , Indicadores e Reagentes , Conformação MolecularRESUMO
Dirhodium(II) caprolactamate (1, Rh 2(cap) 4) with 70% w/w aqueous tert-butyl hydroperoxide (T-HYDRO ) is a highly effective catalytic oxidation protocol for the selective C-H oxidation of alkynes to propargylic ketones. The oxidation occurs readily in aqueous solvent under mild conditions with an inexpensive and easily handled oxidant. Alpha,beta-acetylenic carbonyl compounds are formed in up to 80% isolated yield.