162 research outputs found
Heterogeneous Reductive Isomerization Reaction Using Catalytic Pd/C and H_2
A highly selective catalytic reductive isomerization reaction is described. The extremely mild and neutral reaction conditions (10% Pd/C, H_2, and MeOH at 0 °C) tolerate a wide range of functional groups and generally result in excellent yields. Mechanistic studies suggest that this reaction does not proceed via a stepwise reduction/elimination sequence or a Ï-allylpalladium intermediate
Development of an Enantiodivergent Strategy for the Total Synthesis of (+)- and (â)-Dragmacidin F from a Single Enantiomer of Quinic Acid
An enantiodivergent strategy for the total chemical synthesis of both (+)- and (â)-dragmacidin F beginning from a single enantiomer of quinic acid has been developed and successfully implemented. Although unique, the synthetic routes to these antipodes share a number of key features, including novel reductive isomerization reactions, Pd(II)-mediated oxidative carbocyclization reactions, halogen-selective Suzuki couplings, and high-yielding late-stage Neber rearrangements
The Total Synthesis of (+)-Dragmacidin F
The first total synthesis of (+)-dragmacidin F has been accomplished, establishing the absolute configuration of this biologically important, antiviral marine alkaloid. The convergent route described features a palladium-mediated oxidative pyrrole carbocylization reaction to construct the [3.3.1] bicycle, as well as a highly selective Suzuki coupling to build the carbon skeleton of the natural product. A late-stage Neber rearrangement allows for the facile installation of the aminoimidazole moiety to provide (+)-dragmacidin F
The Total Synthesis of (+)-Dragmacidin F
The first total synthesis of (+)-dragmacidin F has been accomplished, establishing the absolute configuration of this biologically important, antiviral marine alkaloid. The convergent route described features a palladium-mediated oxidative pyrrole carbocylization reaction to construct the [3.3.1] bicycle, as well as a highly selective Suzuki coupling to build the carbon skeleton of the natural product. A late-stage Neber rearrangement allows for the facile installation of the aminoimidazole moiety to provide (+)-dragmacidin F
Heterogeneous Reductive Isomerization Reaction Using Catalytic Pd/C and H_2
A highly selective catalytic reductive isomerization reaction is described. The extremely mild and neutral reaction conditions (10% Pd/C, H_2, and MeOH at 0 °C) tolerate a wide range of functional groups and generally result in excellent yields. Mechanistic studies suggest that this reaction does not proceed via a stepwise reduction/elimination sequence or a Ï-allylpalladium intermediate
The Palladium-Catalyzed Aerobic Kinetic Resolution of Secondary Alcohols: Reaction Development, Scope, and Applications
The first palladium-catalyzed enantioselective oxidation of secondary alcohols has been developed, utilizing the readily available diamine (-)-sparteine as a chiral ligand and molecular oxygen as the stoichiometric oxidant. Mechanistic insights regarding the role of the base and hydrogen-bond donors have resulted in several improvements to the original system. Namely, addition of cesium carbonate and tert-butyl alcohol greatly enhances reaction rates, promoting rapid resolutions. The use of chloroform as solvent allows the use of ambient air as the terminal oxidant at 23 °C, resulting in enhanced catalyst selectivity. These improved reaction conditions have permitted the successful kinetic resolution of benzylic, allylic, and cyclopropyl secondary alcohols to high enantiomeric excess with good-to-excellent selectivity factors. This catalyst system has also been applied to the desymmetrization of meso-diols, providing high yields of enantioenriched hydroxyketones
Enduring mental health: Prevalence and prediction.
We review epidemiological evidence indicating that most people will develop a diagnosable mental disorder, suggesting that only a minority experience enduring mental health. This minority has received little empirical study, leaving the prevalence and predictors of enduring mental health unknown. We turn to the population-representative Dunedin cohort, followed from birth to midlife, to compare people never-diagnosed with mental disorder (N = 171; 17% prevalence) to those diagnosed at 1â2 study waves, the cohort mode (N = 409). Surprisingly, compared to this modal group, never-diagnosed Study members were not born into unusually well-to-do families, nor did their enduring mental health follow markedly sound physical health, or unusually high intelligence. Instead, they tended to have an advantageous temperament/personality style, and negligible family history of mental disorder. As adults, they report superior educational and occupational attainment, greater life satisfaction, and higher-quality relationships. Our findings draw attention to âenduring mental healthâ as a revealing psychological phenotype and suggest it deserves further study
Signatures of arithmetic simplicity in metabolic network architecture
Metabolic networks perform some of the most fundamental functions in living
cells, including energy transduction and building block biosynthesis. While
these are the best characterized networks in living systems, understanding
their evolutionary history and complex wiring constitutes one of the most
fascinating open questions in biology, intimately related to the enigma of
life's origin itself. Is the evolution of metabolism subject to general
principles, beyond the unpredictable accumulation of multiple historical
accidents? Here we search for such principles by applying to an artificial
chemical universe some of the methodologies developed for the study of genome
scale models of cellular metabolism. In particular, we use metabolic flux
constraint-based models to exhaustively search for artificial chemistry
pathways that can optimally perform an array of elementary metabolic functions.
Despite the simplicity of the model employed, we find that the ensuing pathways
display a surprisingly rich set of properties, including the existence of
autocatalytic cycles and hierarchical modules, the appearance of universally
preferable metabolites and reactions, and a logarithmic trend of pathway length
as a function of input/output molecule size. Some of these properties can be
derived analytically, borrowing methods previously used in cryptography. In
addition, by mapping biochemical networks onto a simplified carbon atom
reaction backbone, we find that several of the properties predicted by the
artificial chemistry model hold for real metabolic networks. These findings
suggest that optimality principles and arithmetic simplicity might lie beneath
some aspects of biochemical complexity
Status of Muon Collider Research and Development and Future Plans
The status of the research on muon colliders is discussed and plans are
outlined for future theoretical and experimental studies. Besides continued
work on the parameters of a 3-4 and 0.5 TeV center-of-mass (CoM) energy
collider, many studies are now concentrating on a machine near 0.1 TeV (CoM)
that could be a factory for the s-channel production of Higgs particles. We
discuss the research on the various components in such muon colliders, starting
from the proton accelerator needed to generate pions from a heavy-Z target and
proceeding through the phase rotation and decay ()
channel, muon cooling, acceleration, storage in a collider ring and the
collider detector. We also present theoretical and experimental R & D plans for
the next several years that should lead to a better understanding of the design
and feasibility issues for all of the components. This report is an update of
the progress on the R & D since the Feasibility Study of Muon Colliders
presented at the Snowmass'96 Workshop [R. B. Palmer, A. Sessler and A.
Tollestrup, Proceedings of the 1996 DPF/DPB Summer Study on High-Energy Physics
(Stanford Linear Accelerator Center, Menlo Park, CA, 1997)].Comment: 95 pages, 75 figures. Submitted to Physical Review Special Topics,
Accelerators and Beam
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