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Anke Schmauder Dipl.‐Chem. L. David Sibley Prof. Martin E. Maier Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(14):4328-4336
The first total synthesis of the cyclodepsipeptide chondramide A ( 2 b ) is described. This depsipeptide is composed of four subunits, namely L ‐alanine, N‐Me‐D ‐tryptophan, 3‐amino‐2‐methoxy‐propionic acid (β‐tyrosine derivative), and a 7‐hydroxy‐alkenoic acid. While the configuration of the stereogenic centers in the 7‐hydroxy‐alkenoic acid were known, the configuration of the tyrosine derivative required clarification and turned out to be (2S,3R) or (2L ,3L ), respectively. The synthesis of the 3‐amino‐2‐methoxy‐3‐arylpropanoic ester 20 b relied on an asymmetric dihydroxylation yielding diol ent‐ 15 a followed by a regioselective Mitsunobu substitution leading to 3‐azido‐2‐hydroxypropanoate 18 b . We could also show that the ester bond in the seco compound 26 b can be fashioned by a Mitsunobu esterification by using hydroxy ester (7S)‐ 7 and the tripeptide acid 25 b . This synthesis should allow for the preparation of various analogues. 相似文献
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An experiment suitable for first-year students is reported. In this activity, students use a molecular modeling program to compute infrared spectra for a series of molecules. From the data obtained, students generate a group frequency chart and use it to identify unknowns. This provides students with an introduction to vibrational spectroscopy and the use of molecular modeling. 相似文献
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Gary A. Epling Michele T. Sibley Thomas T. Chou Anil Kumar 《Photochemistry and photobiology》1988,47(4):491-495
Abstract— Abstract-The products of photochemical reaction of a family of phototoxic tricyclic antidepressants have been determined, both in the presence and absence of oxygen. Under all conditions photofrag-mentation of the phototoxic compounds is an important reaction-in some cases it is virtually the only photoreaction observed. The mechanism of photoreaction appears to involve excited state electron transfer from the side chain to give a reactive exciplex, which fragments via both radical and ionic pathways. These reactive intermediates are likely to contribute to the in vivo phototoxicity of these compounds. 相似文献
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Fluorozirconate (ZBLA) and fluorohafnate (HBL) glasses have been exposed to ionizing radiation at room temperature, and the resulting defects have been characterized using optical absorption and electron spin resonance techniques. Prominent absorption bands were found to peak in the ultraviolet at 290 nm for the ZBLA glass and at 240 and 310 nm for the HBL glass. Two major electron spin resonance spectra having g values of 1.883 and 2.043 were induced in the HBL glass. Similar electron spin resonance spectra were found in the ZBLA glass. A third spectrum with a g value of 2.008 was also observed in the ZBLA material. The optical and electron spin resonance spectra in these glasses thermally annealed between room temperature and 300°C. Possible models for the defects are discussed. 相似文献
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A family of 12 phototoxic quinolinemethanol antimalarials and three other non-phototoxic clinically used compounds were irradiated in the presence of red blood cells to determine if the resulting hemolysis would be a reliable predictor of phototoxicity. The most phototoxic compounds from in vivo tests were also the most phototoxic in this study. Quinine caused little RBC lysis, paralleling its non-phototoxicity in humans. The quinolinemethanol-induced photohemolysis occurs both in the presence and absence of oxygen. Enriching the RBC with BHA and cholesterol was particularly effective at protecting the cells from photohemolysis. Other compounds offered some measure of protection, while superoxide dismutase and sodium azide, among others, afforded no protection. 相似文献
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[reaction: see text] Fe(III)-mediated ring opening of cyclopropyl ethers bearing a phenyl-substituted butenyl side chain leads to the generation of beta-keto radicals that undergo 5-exo cyclization followed by a novel cascade sequence resulting in the formation of tricyclic ethers. 相似文献
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The optical properties of irradiated RbMgF3:Eu2+ and KMgF3:Eu2+ have been investigated. Previous research has shown that Eu2+ ions in unirradiated RbMgF3 give rise to broad band absorption around 250 nm and sharp intense line emission at 360 nm. When this material is irradiated little or no change occurs in the 250 nm absorption, but the lifetime of the Eu2+ 360 nm transition is reduced. In addition, new emission is observed at 680 nm. In the case of irradiated KMgF3:Eu2+ two new emission bands are observed at 600 and 800 nm. All of these transitions have short lifetimes and are not due to Eu3+ ions. 相似文献
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C.E. Gough R.J. OrmenoA. Sibley M. HeinS. NishiZaki Y. Maeno 《Journal of Physics and Chemistry of Solids》2002,63(12):2187-2193
A hollow dielectric resonator technique has been developed for accurate measurements of the complex microwave surface impedance of novel superconductors from 2 to 20 GHz down to 100 mK. Illustrative measurements of the antiferromagnetic ordering and spin-dynamics of Gd ions in GdBa2Cu3O7 and of microwave penetration and losses in MgB2 wires and high quality single crystals of Sr2RuO4 are presented. Measurements on Sr2RuO4 imply an unchanged electron relaxation time τ on entering the superconducting state, a power law temperature dependence of the normal state fraction implying nodes in the superconducting order parameter, and residual low temperature losses on increasing frequency. 相似文献
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The absorption spectrum of RbMnF3 and the excitation spectra of the system RbMgxMn1-xF3 at 10 K as well as the fluorescence spectra and lifetimes of Mn2+ in the systems RbMgxMn1-xF3 and KMgxMn1-xF3 in the region 10–300 K were measured. The lifetime and fluorescence temperature dependence suggest that the origin of the fluorescence occurs at Mn2+ sites slightly perturbed by impurity ions and that a non-radiative energy transfer mechanism is responsible for the observed thermal quenching. By using different Mn2+ concentrations in the above systems the dependence of the energy transfer on the Mn2+ concentration is shown. Finally, a preliminary observation on laser stimulated Mn2+ luminescence in the system RbMgxMn1-xF3 is reported. 相似文献