排序方式: 共有130条查询结果,搜索用时 15 毫秒
61.
Dr. Johannes Preindl Saskia Schulthoff Conny Wirtz M. Sc. Julia Lingnau Prof. Alois Fürstner 《Angewandte Chemie (International ed. in English)》2017,56(26):7525-7530
Orevactaene and epipyrone A were previously thought to comprise the same polyunsaturated tail but notably different C-glycosylated 4-hydroxy-2-pyrone head groups. Total synthesis now shows that the signature bicyclic framework assigned to orevactaene is a chimera; the compound is almost certainly identical with epipyrone A, whose previously unknown stereochemistry has also been established during this study. Key to success was the ready formation of the bicyclic core of putative orevactaene by a sequence of two alkyne cycloisomerization reactions using tungsten and gold catalysis. Equally important was the flexibility in the assembly process gained by the use of heterobimetallic polyunsaturated modules whose termini could be selectively and consecutively addressed in a practical one-pot cross-coupling sequence. 相似文献
62.
Dr. Mariusz Jaremko Dr. Łukasz Jaremko Dr. Saskia Villinger Christian D. Schmidt Prof. Dr. Christian Griesinger Dr. Stefan Becker Prof. Dr. Markus Zweckstetter 《Angewandte Chemie (International ed. in English)》2016,55(35):10518-10521
15N spin‐relaxation rates are demonstrated to provide critical information about the long‐range structure and internal motions of membrane proteins. Combined with an improved calculation method, the relaxation‐rate‐derived structure of the 283‐residue human voltage‐dependent anion channel revealed an anisotropically shaped barrel with a rigidly attached N‐terminal helix. Our study thus establishes an NMR spectroscopic approach to determine the structure and dynamics of mammalian membrane proteins at high accuracy and resolution. 相似文献
63.
64.
65.
Prof. Dr. Oliver Trapp Dr. Saskia Lamour Dr. Frank Maier Dr. Alexander F. Siegle Dr. Kerstin Zawatzky Prof. Dr. Bernd F. Straub 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(68):15871-15880
Chemical reactions that lead to a spontaneous symmetry breaking or amplification of the enantiomeric excess are of fundamental interest in explaining the formation of a homochiral world. An outstanding example is Soai's asymmetric autocatalysis, in which small enantiomeric excesses of the added product alcohol are amplified in the reaction of diisopropylzinc and pyrimidine-5-carbaldehydes. The exact mechanism is still in dispute due to complex reaction equilibria and elusive intermediates. In situ high-resolution mass spectrometric measurements, detailed kinetic analyses and doping with in situ reacting reaction mixtures show the transient formation of hemiacetal complexes, which can establish an autocatalytic cycle. We propose a mechanism that explains the autocatalytic amplification involving these hemiacetal complexes. Comprehensive kinetic experiments and modelling of the hemiacetal formation and the Soai reaction allow the precise prediction of the reaction progress, the enantiomeric excess as well as the enantiomeric excess dependent time shift in the induction period. Experimental structural data give insights into the privileged properties of the pyrimidyl units and the formation of diastereomeric structures leading to an efficient amplification of even minimal enantiomeric excesses, respectively. 相似文献
66.
Dr. Thomas N. Snaddon Dr. Philipp Buchgraber Saskia Schulthoff Conny Wirtz Dr. Richard Mynott Prof. Dr. Alois Fürstner 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(40):12133-12140
A productive total synthesis of both enantiomers of berkelic acid ( 1 ) is outlined that takes the structure revision of this bioactive fungal metabolite previously proposed by our group into account. The successful route relies on a fully optimized triple‐deprotection/1,4‐addition/spiroacetalization cascade reaction sequence, which delivers the tetracyclic core 32 of the target as a single isomer in excellent yield. The required cyclization precursor 31 is assembled from the polysubstituted benzaldehyde derivative 20 and methyl ketone 25 by an aldol condensation, in which the acetyl residue in 20 transforms from a passive protecting group into an active participant. Access to fragment 25 takes advantage of the Collum–Godenschwager variant of the ester enolate Claisen rearrangement, which clearly surpasses the classical Ireland–Claisen procedure in terms of diastereoselectivity. Although it is possible to elaborate 32 into the target without any additional manipulations of protecting groups, a short detour consisting in the conversion of the phenolic ? OH into the corresponding TBS‐ether is beneficial. It tempers the sensitivity of the compound toward oxidation and hence improves the efficiency and reliability of the final stages. Orthogonal ester groups for the benzoate and the aliphatic carboxylate terminus of the side chain secure an efficient liberation of free berkelic acid in the final step of the route. 相似文献
67.
Ruben t’Kindt Andris Jankevics Richard A. Scheltema Liang Zheng David G. Watson Jean-Claude Dujardin Rainer Breitling Graham H. Coombs Saskia Decuypere 《Analytical and bioanalytical chemistry》2010,398(5):2059-2069
Comparative metabolomics of Leishmania species requires the simultaneous identification and quantification of a large number of intracellular metabolites. Here,
we describe the optimisation of a comprehensive metabolite extraction protocol for Leishmania parasites and the subsequent optimisation of the analytical approach, consisting of hydrophilic interaction liquid chromatography
coupled to LTQ-orbitrap mass spectrometry. The final optimised protocol starts with a rapid quenching of parasite cells to
0 °C, followed by a triplicate washing step in phosphate-buffered saline. The intracellular metabolome of 4 × 107 parasites is then extracted in cold chloroform/methanol/water 20/60/20 (v/v/v) for 1 h at 4 °C, resulting in both cell disruption and comprehensive metabolite dissolution. Our developed metabolomics
platform can detect approximately 20% of the predicted Leishmania metabolome in a single experiment in positive and negative ionisation mode.
相似文献
68.
69.
Lindström F Thurnhofer S Vetter W Gröbner G 《Physical chemistry chemical physics : PCCP》2006,8(41):4792-4797
Here, we exploit the non-invasive techniques of solid-state NMR (nuclear magnetic resonance) and differential scanning calorimetry (DSC) to study the effect of free iso and ante-iso branched chain fatty acids (BCFAs) on the physicochemical properties of lipid membranes. Free fatty acids are present in biological membranes at low abundance, but can influence the cellular function by modulating the membrane organization. Solid state NMR spectra of dimyristoylphosphatidylcholine (DMPC) lipid membranes containing either free 12-methyltetradecanoic acid (a15:0) or free 13-methyltetradecanoic acid (i15:0), show significant differences in their impact on the lipid bilayer. Chain order profiles obtained by deuterium NMR on fully deuterated DMPC-d(67) bilayers revealed an ordering effect induced by both fatty acids on the hydrophobic membrane core. This behavior was also visible in the corresponding DSC thermograms where the main phase transition of DMPC bilayers-indicative of the hydrophobic membrane region-was shifted to higher temperatures, with the iso isomer triggering more pronounced changes as compared to the ante-iso isomer. This is probably due to a higher packing density in the core of the lipid bilayer, which causes reduced diffusion across membranes. By utilizing the naturally occurring spin reporters nitrogen-14 and phosphorus-31 present in the hydrophilic DMPC headgroup region, even fatty acid induced changes at the membrane interface could be detected, an observation reflecting changes in the lipid headgroup dynamics. 相似文献
70.
Stortelder A Hendriks J Buijs JB Bulthuis J Gooijer C van der Vies SM van der Zwan G 《The journal of physical chemistry. B》2006,110(49):25050-25058
The bacteriophage T4 capsid protein gp23 was studied using time-resolved and steady-state fluorescence of the intrinsic protein fluorophore tryptophan. In-vitro gp23 consists mostly of monomers at low temperature but forms hexamers at room temperature. To extend our knowledge of the structure and hexamerization characteristics of gp23, the temperature-dependent fluorescence properties of a tryptophan mutant (W13V) were compared to those of wild-type gp23. The W13V mutation is located in the N-terminal part of the protein, which is cleaved off after prohead formation in the live bacteriophage. Results show that W13 plays a role in the hexamerization process but is not needed to stabilize the hexamer once it is formed. Furthermore, besides the monomer-to-hexamer temperature transition (15-23 degrees C and 12-43 degrees C for wild-type and W13V gp23, respectively), we were able to observe denaturation of the N-terminus in hexameric wild-type gp23 around 40 degrees C. In addition, with the aid of a recently published homology model of gp23, the lifetimes obtained from time-resolved fluorescence measurements could tentatively be assigned to specific tryptophan residues. 相似文献