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Eberhard Reimann Wolfgang Erdle Eugen Hargasser Hermann Lotter 《Monatshefte für Chemie / Chemical Monthly》2002,133(7):1017-1030
Summary. The stereoselective synthesis of cis-ergoline is presented. Starting from rac-N-benzoyl tryptophan methyl ester, the key compound indolinylmethylpyridin-3-one was prepared via a seven-step reaction in good yield. Since its cyclization to the desired ergolinone failed, the key compound was reduced
to yield the two diastereomeric pyridin-3-ols; only one of them cyclized in trifluoromethanesulfonic acid, affording cis-ergoline. Catalytic hydrogenation of the latter gave N,N′-dimethyldihydroergoline, the X-ray crystallography of which revealed both the correct structure and identical relative configurations
at C-5a and C-6a (SS or RR). Hydroboration and subsequent perruthenate oxidation of the Δ9-ergoline provided access to the regioisomeric ergolinols and ergolinones.
Received December 27, 2001. Accepted January 15, 2002 相似文献
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86.
Pugliesi I Krok P Lochbrunner S Błaszczyk A von Hänisch C Mayor M Riedle E 《The journal of physical chemistry. A》2010,114(48):12555-12560
The ultrafast fluorescence quenching of 2,6-sulfanyl-core-substituted naphthalenediimides was investigated by transient spectroscopy. We find a strong dependence of the relaxation on the chemical structure of the substituent. Direct linking of an aryl rest to the sulfur atom leads to a strong red shift of the fluorescence in 1 ps and the disappearance of the emission in 5-7 ps depending on the polarity and viscosity of the solvent. This complex behavior is interpreted with the help of quantum chemical calculations. The calculations suggest that the initial relaxation corresponds to a planarization of the substituents and an associated partial electron transfer. This is followed by a twisting of the phenylsulfanyl substituents out of the molecular plane that allows a complete localization of the electron-donating orbital on the aryl group. Finally the back transfer happens in another 5-7 ps. For an additional methylene spacer group between the sulfur and the aryl, this sequence of relaxation steps is not possible and a simple exponential decay, slower by about 1 order of magnitude, is found. 相似文献
87.
Verch A Hahn H Krause E Cölfen H Börner HG 《Chemical communications (Cambridge, England)》2010,46(47):8938-8940
Self-assembled peptide-polymer nanotapes of poly(ethylene oxide)-peptide conjugates are modified by a simple amine-azide transfer to create azide-containing nanofibres, which provide a platform for modular functionalization as demonstrated by the introduction of different carboxyl bearing entities to modulate the calcium binding properties of the nanotapes. 相似文献
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Susanne Friedreich D��niel Barna Andreas Dax Ryu Hayano Dezs? Horv��th Masaki Hori Bertalan Juh��sz Oswald Massiczek Anna S��t��r Thomas Pask Eberhard Widmann 《Hyperfine Interactions》2011,199(1-3):337-346
The spin magnetic moment $\mu^{\overline{p}}_{s}$ of the antiproton can be determined by comparing the measured transition frequencies in $\overline{p}^4$ He?+? with three-body QED calculations. A comparison between the proton and antiproton can then be used as a test of CPT invariance. The highest measurement precision of the difference between the proton and the antiproton spin magnetic moments to date is 0.3%. A new experimental value of the spin magnetic moment of the antiproton was obtained as $\mu^{\overline{p}}_{s} = -2.7862(83)\mu_{N}$ , slightly better than the previously best measurement. This agrees with $\mu^{p}_{s}$ within 0.24%. In 2009, a new measurement with antiprotonic 3He has been started. A comparison between the theoretical calculations and experimental results would lead to a stronger test of the theory and address systematic errors therein. A measurement of this state will be the first HF measurement on $\overline{p}^3$ He?+?. We report here on the new experimental setup and the first tests. 相似文献
89.
The usage of flexible bodies in Multibody simulations (MBS) has widely increased their industrial application. Finite Element (FE) models with up to 10 million degrees of freedom (DOF) and some hundred million nonzero matrix entries are used to describe the flexible bodies. Before such a model can be included into an MBS, the number of DOF must be reduced to an appropriate size. Using modal reduction often the critical issue arises which modes to choose while Component Mode Synthesis based methods often lead to a relatively big size of the resulting model. Alternative methods using Moment Matching and Balanced Truncation can result in a smaller size while still remaining accurate enough. Sometimes these matrices are so huge that they can not even be stored in one computers main memory. The calculation of the necessary orthogonal Krylov subspaces needs an LU factorization which is also very memory intensive. To meet these requirements, distributed computation is used which also shortens the computational time of the reduced process. In this work, an industrial relevant FE model is reduced to a much smaller size using alternative methods. Accuracy is verified by comparing the frequency response in a defined frequency range of the original and the reduced model. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
90.
Natashia L. Boland Andrew C. Eberhard Faramroze G. Engineer Matteo Fischetti Martin W. P. Savelsbergh Angelos Tsoukalas 《Mathematical Programming Computation》2014,6(3):255-279
The feasibility pump (FP) has proved to be an effective method for finding feasible solutions to mixed integer programming problems. FP iterates between a rounding procedure and a projection procedure, which together provide a sequence of points alternating between LP feasible but fractional solutions, and integer but LP infeasible solutions. The process attempts to minimize the distance between consecutive iterates, producing an integer feasible solution when closing the distance between them. We investigate the benefits of enhancing the rounding procedure with a clever integer line search that efficiently explores a large set of integer points. An extensive computational study on benchmark instances demonstrates the efficacy of the proposed approach. 相似文献