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31.
32.
Guindon Y Ogilvie WW Bordeleau J Cui WL Durkin K Gorys V Juteau H Lemieux R Liotta D Simoneau B Yoakim C 《Journal of the American Chemical Society》2003,125(2):428-436
Johnson-type acetals derived from dimethyl tartrate give, after opening with Me(2)BBr and cuprate displacement, secondary alcohols with high diastereoselectivity (>30:1). The mechanism proposed for the induction of diastereoselectivity is downstream from the ring fission. It implies a direct participation of the Lewis acid as a source of nucleophile and the stereospecific transformation of the resulting bromo acetal through an invertive and temperature-dependent process. The acetals are prepared by reaction of the desired aldehyde with dimethyl tartrate. Removal of the auxiliary is accomplished through SmI(2) reduction or by an addition-elimination protocol using methoxide. 相似文献
33.
High-performance liquid chromatographic analysis of neurotransmitter amino acids in brain 总被引:2,自引:0,他引:2
Rapid and selective determination of neurotransmitter amino acids in rat and human brain is accomplished by pre-column derivatization with o-phthaldehyde-3-mercaptopropionic acid, reversed-phase high-performance liquid chromatographic separation, and fluorimetric detection. Aspartate, taurine, glutamate, and glycine are determined in less than 12 min with intra- and inter-assay precisions of 2.1-9.5% and 4.2-9.2%, respectively. gamma-Aminobutyric acid is determined in less than 8 min with intra- and inter-assay precisions of 1.6 and 11.7%, respectively. Both assays utilize internal standards and require a minimum of sample preparation. 相似文献
34.
Modulated imaging: quantitative analysis and tomography of turbid media in the spatial-frequency domain 总被引:2,自引:0,他引:2
Experiments performed on turbid phantoms demonstrate that spatially modulated illumination facilitates quantitative wide-field optical property mapping and tomographic imaging in turbid media. 相似文献
35.
Ahrens LA Aronson SH Connolly PL Gibbard BG Murtagh MJ Murtagh S Terada S White DH Callas JL Cutts D Hoftun JS Lanou RE Shinkawa T Amako K Kabe S Nagashima Y Suzuki Y Tatsumi S Abe K Beier EW Doughty DC Durkin LS Heagy SM Hurley M Mann AK Newcomer FM Williams HH York T Hedin D Marx MD Stern E 《Physical review letters》1985,54(1):18-21
36.
Reactive scattering of O atoms with ICl molecules has been studied at an initial translational energy E = 40 kJ mol-1 using a supersonic beam of O atoms seeded in He and at E = 15 kJ mol-1 using O atoms seeded in Ne. Velocity distributions of OI product were measured by cross-correlation time-of-flight analysis. Full contour maps of the differential reaction cross-section have been obtained which show peaking almost equally in the forward and backward directions at both initial translational energies. The product translational energy distributions are consistent with a long-lived O-I-Cl collision complex dissociating via a loose transition state. The stability of the O-I-Cl complex is attributed to the low electronegativity of the central I atom compared with the peripheral atoms. This electronegativity ordering rule also determines the stability of the intermediates in the other reactions of oxygen atoms with halogen molecules. The mild peaking of the product angular distributions for O + ICl and IBr indicates that collision complexes have quite modest collision angular momenta L ~ 40 ? corresponding to impact parameters b ~ 1·4 Å and that the angular momentum of the OI molecule in the loose transition state may be approximately half the product orbital angular momentum. 相似文献
37.
An analytical iterative procedure has been established to determine the amplitude of a laser beam propagating through an active
medium. The treatment is valid for both homogeneous and inhomogeneous broadening, and for arbitrary inhomogeneities of the
parameters characterizing the active medium, namely, the refractive index, the small-signal gain and the saturation intensity.
After a supplementary approximation, a thin-sheet gain approach is derived from the first iteration. The formalism enables
us to provide analytical criteria for evaluating both the accuracy of each iteration and the propagation distances for which
the thin-sheet solution can be used.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
38.
Collins PY Patel V Joestl SS March D Insel TR Daar AS;Scientific Advisory Board the Executive Committee of the Grand Challenges on Global Mental Health Anderson W Dhansay MA Phillips A Shurin S Walport M Ewart W Savill SJ Bordin IA Costello EJ Durkin M Fairburn C Glass RI Hall W Huang Y Hyman SE Jamison K Kaaya S Kapur S Kleinman A Ogunniyi A Otero-Ojeda A Poo MM Ravindranath V Sahakian BJ Saxena S Singer PA Stein DJ 《Nature》2011,475(7354):27-30
39.
Iraj Behroz Dr. Patrick Durkin Dr. Stefan Grätz Maria Seidel Lida Rostock Marcello Spinczyk Dr. John B. Weston Prof. Dr. Roderich D. Süssmuth 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(72):16538-16543
Albicidin is a recently described natural product that strongly inhibits bacterial DNA gyrase. The pronounced activity, particularly against Gram-negative bacteria, turns it into a promising lead structure for an antibacterial drug. Hence, structure–activity relationship studies are key for the in-depth understanding of structural features/moieties affecting gyrase inhibition, antibacterial activity and overcoming resistance. The 27 newly synthesized albicidins give profound insights into possibilities for variations of the C-terminus. Furthermore, in the present study, a novel derivative has been identified as overcoming resistance posed by the Klebsiella-protease AlbD. Structural modifications include, for example, azahistidine replacing the previous instable cyanoalanine as the central amino acid, as well as a triazole amide bond isostere between building blocks D and E. 相似文献