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91.
Felix Anderl Sylvester Größl Conny Wirtz Prof. Alois Fürstner 《Angewandte Chemie (International ed. in English)》2018,57(33):10712-10717
The assigned structure of the dinoflagellate‐derived toxin belizentrin was prepared by total synthesis in form of the corresponding methyl ester for stability reasons. The successful route features an unusual solution for the preparation of a recalcitrant ylide on a C‐glycosidic segment; moreover, it involves an asymmetric hetero‐Diels–Alder reaction en route to the tertiary hemiacetal substructure, a Negishi cross‐coupling of two elaborate building blocks, and a macrocyclization based on an intramolecular aminolysis of a spirolactone. A modified Kocienski olefination ultimately allowed the polyol side chain to be attached to the macrocycle although this transformation faced the exceptional base sensitivity of this polyunsaturated target compound. 相似文献
92.
Ohne Zusammenfassung 相似文献
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94.
Fürstner A Majima K Martín R Krause H Kattnig E Goddard R Lehmann CW 《Journal of the American Chemical Society》2008,130(6):1992-2004
Reaction of ferrocene with lithium in the presence of either ethylene or COD allows the Fe(0)-ate complexes 1 and 4 to be prepared on a large scale, which turned out to be excellent catalysts for a variety of Alder-ene, [4+2], [5+2], and [2+2+2] cycloadditon and cycloisomerization reactions of polyunsaturated substrates. The structures of ferrates 1 and 4 in the solid-state reveal the capacity of the reduced iron center to share electron density with the ligand sphere. This feature, coupled with the kinetic lability of the bound olefins, is thought to be responsible for the ease with which different enyne or diyne substrates undergo oxidative cyclization as the triggering event of the observed skeletal reorganizations. This mechanistic proposal is corroborated by highly indicative deuterium labeling experiments. Moreover, it was possible to intercept two different products of an oxidative cyclization manifold with the aid of the Fe(+1) complex 6, which, despite its 17-electron count, also turned out to be catalytically competent in certain cases. The unusual cyclobutadiene complex 38 derived from 6 and tolane was characterized by X-ray crystallography. 相似文献
95.
Fürstner A Kirk D Fenster MD Aïssa C De Souza D Nevado C Tuttle T Thiel W Müller O 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(1):135-149
Deliberate digression from the blueprint of the total syntheses of latrunculin A (1) and latrunculin B (2) reported in the accompanying paper allowed for the preparation of a focused library of "latrunculin-like" compounds, in which all characteristic structural elements of these macrolides were subject to pertinent molecular editing. Although all previously reported derivatives of 1 and 2 were essentially devoid of any actin-binding capacity, the synthetic compounds presented herein remain fully functional. One of the designer molecules with a relaxed macrocyclic backbone, that is compound 44, even surpasses latrunculin B in its effect on actin while being much easier to prepare. This favorable result highlights the power of "diverted total synthesis" as compared to the much more widely practiced chemical modification of a given lead compound by conventional functional group interconversion. A computational study was carried out to rationalize the observed effects. The analysis of the structure of the binding site occupied by the individual ligands on the G-actin host shows that latrunculin A and 44 both have similar hydrogen-bond network strengths and present similar ligand distortion. In contrast, the H-bond network is weaker for latrunculin B and the distortion of the ligand from its optimum geometry is larger. From this, one may expect that the binding ability follows the order 1 >/= 44 > 2, which is in accord with the experimental data. Furthermore, the biological results provide detailed insights into structure/activity relationships characteristic for the latrunculin family. Thus, it is demonstrated that the highly conserved thiazolidinone ring of the natural products can be replaced by an oxazolidinone moiety, and that inversion of the configuration at C16 (latrunculin B numbering) is also well accommodated. From a purely chemical perspective, this study attests to the maturity of ring-closing alkyne metathesis (RCAM) catalyzed by a molybdenum alkylidyne complex generated in situ, which constitutes a valuable tool for advanced organic synthesis and natural product chemistry. 相似文献
96.
Fürstner A Nagano T Müller C Seidel G Müller O 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(5):1452-1462
A comparative investigation shows that hydroxylated 10-membered lactones modeled around the fungal metabolites microcarpalide (1) and pinolidoxin (2) are endowed with selective actin-binding properties. Although less potent than the marine natural product latrunculin A, which represents the standard in the field, nonenolides of this type are significantly less toxic and accommodate substantial structural editing. Most notable is the fact that even an intramolecular transesterification with formation of a hydroxylated butanolide skeleton does not annihilate their microfilament disrupting capacity. This finding calls for a reinvestigation of the biological profile of other fungal metabolites that embody a similar motif. Microcarpalide (1) serving as the calibration point for this comparative study was prepared by total synthesis based on ring-closing metathesis (RCM) as the key step. The chosen route favorably compares to previous approaches to this target and provides further support for the notion that the (E,Z)-configuration of a medium-sized cycloalkene can be controlled by proper choice of the catalyst as previously outlined by our group. 9-epi-Microcarpalide 26 and furanone 27 as representative examples of the "natural productlike" compounds investigated herein have been characterized by crystal structure analysis. 相似文献
97.
Adsorption of proteins on surfaces of hydrophobic interaction chromatography media is at least a two-stage process. Application of pure protein pulses (bovine serum albumin and beta-lactoglobulin) to hydrophobic interaction chromatography media yielded two chromatographic peaks at low salt concentrations. At these salt concentrations, the adsorption process is affected by a second reaction, which can be interpreted as protein spreading or partial unfolding of the protein. The kinetic constants of the spreading reaction were derived from pulse response experiments at different residence times and varying concentrations by applying a modified adsorption model considering conformational changes. The obtained parameters were used to calculate uptake and breakthrough curves for spreading proteins. Although these parameters were determined at low saturation of the column, predictions of overloaded situations could match the experimental runs satisfactorily. Our findings suggest that proteins which are sensitive to conformational changes should be loaded at high salt concentrations in order to accelerate the adsorption reaction and to obtain steeper breakthrough curves. 相似文献
98.
We investigate the dynamics of a hauling rope modelled as an inextensible completely flexible string and calculate the first natural frequencies. Furthermore we discuss the sensitivity of the model on the operating speed of the ropeway. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
99.
100.
Alois Fadini 《无机化学与普通化学杂志》2001,627(4):572-573
For Analytical Calculation of Assignments of Vibrational Spectroscopic Frequencies Using the normal coordinate treatment we calculate assignments of vibrational spectroscopic frequencies of the systems X3 ( D 3h) and X4 ( T d) and partially of the systems XY4 ( D 4h) and XY6 ( O h). 相似文献