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121.
Gottfried J. Palm Maren Thomsen Leona Berndt Winfried Hinrichs 《Molecules (Basel, Switzerland)》2022,27(22)
The bacterial chalcone isomerase (CHI) from Eubacterium ramulus catalyses the first step in a flavanone-degradation pathway by a reverse Michael addition. The overall fold and the constitution of the active site of the enzyme completely differ from the well-characterised chalcone isomerase of plants. For (+)-taxifolin, CHI catalyses the intramolecular ring contraction to alphitonin. In this study, Fwe perform crystal structure analyses of CHI and its active site mutant His33Ala in the presence of the substrate taxifolin at 2.15 and 2.8 Å resolution, respectively. The inactive enzyme binds the substrate (+)-taxifolin as well defined, whereas the electron density maps of the native CHI show a superposition of substrate, product alphitonin, and most probably also the reaction intermediate taxifolin chalcone. Evidently, His33 mediates the stereospecific acid-base reaction by abstracting a proton from the flavonoid scaffold. The stereospecificity of the product is discussed. 相似文献
122.
Andrés Aragoneses Diego Pavón Winfried Zimdahl 《General Relativity and Gravitation》1998,30(2):299-310
In this article we determine the dominating modes of the cosmological perturbations in different transition eras of the universe evolution (namely, radiation-dust, dust-vacuum, dust-K-matter, and K-matter-vacuum) in a covariant and gauge-invariant manner. 相似文献
123.
We shall prove a rationality result for a quotient of scalar products involving the Ikeda lift of an elliptic cusp form. 相似文献
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We compare function spaces of dominating mixed smoothness and spaces of best approximation with respect to hyperbolic crosses. 相似文献
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The high yield synthesis of the fully soluble acenequinone model compounds 6 and 7 as well as of the corresponding poly(acene quinone) derivative 4 is reported. Some of the diastereomers of 6 and 7 have been isolated and their structures clarified by NMR spectroscopy. This information was used as a basis for assigning the polymer's structure. 相似文献
130.
The reactions of the monosubstituted guanidines2 b-h with methyl acrylate in dimethylformamide or ethanol as solvent preferentially afford 1-substituted 2-amino-5,6-dihydro-4(1H)-pyrimidinones6 b-h. The structures of 1-hexyl- and 1-benzyl-4-pyrimidinones6 c, e and of the picrate of 1-phenylpyrimidinone6 g were proved by comparison with authentic samples, which were prepared from N-substituted ethyl 3-amino-propionates14 c, e andg and cyanamide. Accordingly,6 g is not identical with authentic 2-phenylaminopyrimidinone7 g (prepared from 2-methylthio-4-pyrimidinone10 and 2-thioxo-4-pyrimidinone12 respectively, compare10).N,N-Disubstituted guanidines2 i-m react with methyl acrylate in dimethylformamide as solvent to afford N2,N2-disubstituted 2-amino-5,6-dihydro-4-(1H)-pyrimidinones7 i-m. Action of morpholine-4-carboxamidine (21) on methyl acrylate in ethanol yields 2-morpholinopyrimidinone71 as byproduct and 3-ethoxy-N-[morpholino(amino)methylene]propionamide (91) as mainproduct.
Herrn Prof. Dr.Robert Ott mit den besten Wünschen zum 60. Geburtstag gewidmet. 相似文献