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排序方式: 共有260条查询结果,搜索用时 15 毫秒
91.
Yongzhen Zhang Marcos Gmez‐Redondo Gonzalo Jimnez‐Oss Ana Arda Herman S. Overkleeft Gijsbert A. van der Marel Jesús Jimnez‐Barbero Jeroen D. C. Code 《Angewandte Chemie (International ed. in English)》2020,59(31):12746-12750
Galactosaminogalactan (GAG) is a prominent cell wall component of the opportunistic fungal pathogen Aspergillus fumigatus. GAG is a heteropolysaccharide composed of α‐1,4‐linked galactose, galactosamine and N‐acetylgalactosamine residues. To enable biochemical studies, a library of GAG‐fragments was constructed featuring specimens containing α‐galactose‐, α‐galactosamine and α‐N‐acetyl galactosamine linkages. Key features of the synthetic strategy include the use of di‐tert‐butylsilylidene directed α‐galactosylation methodology and regioselective benzoylation reactions using benzoyl‐hydroxybenzotriazole (Bz‐OBt). Structural analysis of the Gal, GalN and GalNAc oligomers by a combination of NMR and MD approaches revealed that the oligomers adopt an elongated, almost straight, structure, stabilized by inter‐residue H‐bonds, one of which is a non‐conventional C?H???O hydrogen bond between H5 of the residue (i+1) and O3 of the residue (i). The structures position the C‐2 substituents almost perpendicular to the oligosaccharide main chain axis, pointing to the bulk solvent and available for interactions with antibodies or other binding partners. 相似文献
92.
93.
《Magnetic resonance in chemistry : MRC》2002,40(3):169-174
A 3D 1H–13C–1H refocused INEPT transfer experiment is proposed in which the initial coherence transfer of 1H longitudinal to 13C transverse magnetization is tuned to the long‐range 1H, 13C couplings while the reverse INEPT component transfers the magnetization to the directly bonded 1H. Integration of a constant time 1H evolution period into the long‐range coherence transfer interval provides absorption mode signals for each dimension. A 13C purge component at the beginning of the sequence selects for 12C‐bound 1H magnetization that is then transferred to a 13C‐bound hydrogen, thus strongly suppressing the diagonal signals. This experiment is expected to be of particular value for situations in which resonance overlap in the 13C dimension renders 2D long‐range heteronuclear correlation data ambiguous. In combination with a diagonal‐suppressed 3D 1H–13C–1H TOCSY‐HSQC experiment, complete assignment of the ring resonances of the Lewis‐b hexasaccharide was obtained on a 4.2 mM sample using a conventional 500 MHz probe (0.1% ethylbenzene signal‐to‐noise ratio of 600), suggesting its applicability to sub‐millimolar samples using cryoprobe technology. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
94.
Dr. Sameh E. Soliman Dr. Pavol Kováč 《Angewandte Chemie (International ed. in English)》2016,55(41):12850-12853
The first chemical synthesis of the complete protective O‐antigen of a human‐disease‐causing pathogenic bacterium is described. The synthesis involved a protecting‐group strategy that facilitated the regioselectivity of the key transformations, stereoselective glycosylation reactions, and enabled the one‐step global deprotection of the completely assembled, fully protected, phosphorylated hexasaccharide by hydrogenation/hydrogenolysis. The final amino‐group‐functionalized, linker‐equipped antigen was obtained in a form ready for conjugation to suitable carriers, for example, proteins, to yield immunogens. 相似文献
95.
Reagent‐Controlled α‐Selective Dehydrative Glycosylation of 2,6‐Dideoxy‐ and 2,3,6‐Trideoxy Sugars 下载免费PDF全文
Dr. Jason M. Nogueira Marissa Bylsma Danielle K. Bright Prof. Clay S. Bennett 《Angewandte Chemie (International ed. in English)》2016,55(34):10088-10092
We have found that activating either 2,3‐bis(2,3,4‐trimethoxyphenyl)cyclopropenone or 2,3‐bis(2,3,4‐trimethoxyphenyl)cyclopropene‐1‐thione with oxalyl bromide results in the formation of a species that promotes the glycosylation between 2,6‐dideoxy‐sugar hemiacetals and glycosyl acceptors in good yield and high α‐selectivity. Both reactions are mild and tolerate a number of sensitive functional groups including highly acid‐labile 2,3,6‐trideoxy‐sugar linkages. 相似文献
96.
Negative ion MALDI‐TOF MS,ISD and PSD of neutral underivatized oligosaccharides without anionic dopant strategies,using 2,5‐DHAP as a matrix 下载免费PDF全文
Oligosaccharides represent complex class of analytes for mass spectrometric analysis due to the high variety of structural isomers concerning glycosidic linkages and possible branching. A systematic study of the negative ion mode matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry of various neutral oligosaccharides under selection of an appropriate matrix, like 2,5‐dihydroxyacetophenone (2,5‐DHAP) is reported here, without commonly used anion dopant strategies. Nevertheless, we were able to generate relevant in‐source decay (ISD) cross‐ring fragment ions, typically obtained in the negative ion mode. Data observed indicate that the intrinsic property of the terminal non‐reduced aldose is crucial for this behavior. A systematic study of the post source decay (PSD) of molecular, pseudomolecular and ISD cross‐ring cleavage precursor ions is reported here. A direct comparison of the positive and negative ion mode MALDI MS1 and PSD behavior of neutral oligosaccharides could also be performed under the use of the same matrix preparation, because 2,5‐DHAP is fully compatible with positive ion mode acquisition. We found that PSD spectra of deprotonated neutral oligosaccharides obtained in the negative ion mode are richer, because they contained both glycosidic and cross‐ring fragment ions. However, we also found that cross‐ring fragment ions are readily produced in the positive ion mode when potassiated precursor ions were selected. In addition, we show evidence that non‐anionic dopants and specific instrumental parameters can also significantly influence the ISD fragmentation. Taken together, our results should increase our understanding of oligosaccharide behavior in the negative ion mode as well as increase our knowledge regarding many aspects of in‐source MALDI chemistry. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
97.
Klajnert B Appelhans D Komber H Morgner N Schwarz S Richter S Brutschy B Ionov M Tonkikh AK Bryszewska M Voit B 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(23):7030-7041
Maltose-modified poly(propylene imine) (PPI) dendrimers were synthesized by reductive amination of unmodified second- to fifth-generation PPI dendrimers in the presence of excess maltose. The dendrimers were characterized by using (1)H NMR, (13)C NMR, and IR spectroscopies; laser-induced liquid beam ionization/desorption mass spectrometry; dynamic light scattering analyses; and polyelectrolyte titration. Their scaffolds have enhanced molecular rigidity and their outer spheres, at which two maltose units are bonded to the former primary amino groups on the surface, have hydrogen-bond-forming properties. Furthermore, the structural features reveal the presence of a dense shell. Experiments involving encapsulation (1-anilinonaphthalene-8-sulfonic acid) and biological properties (hemolysis and interactions with human serum albumin (HSA) and prion peptide 185-208) were performed to compare the modified with the unmodified dendrimers. These experiments gave the following results: 1) The modified dendrimers entrapped a low-molecular-weight fluorescent dye by means of a dendritic box effect, in contrast to the interfacial uptake characteristic of the unmodified PPI dendrimers. 2) Both low- and high-generation dendrimers containing maltose units showed markedly reduced toxicity. 3) The desirable features of bio-interactions depended on the generation of the dendrimer; they were retained after maltose substitution, but were now mainly governed by nonspecific hydrogen-bonding interactions involving the maltose units. The modified dendrimers interacted with HSA as strongly as the parent compounds and appeared to have potential use as antiprion agents. These improvements will initiate the development of the next platform of glycodendrimers in which apparently contrary properties can be combined, and this will enable, for example, therapeutic products such as more efficient and less toxic antiamyloid agents to be synthesized. 相似文献
98.
Dr. Tapan Kumar Pradhan 《European journal of organic chemistry》2023,26(24):e202300146
Higher carbon saccharide 3-deoxy-d -manno-oct-2-ulosonic acid (Kdo) is a structural unit of bacterial lipopolysaccharides (LPSs) and capsular polysaccharides (CPSs). Kdo is present in the inner core region of LPSs, and this region is structurally conserved. Being non-mammalian in origin, Kdos are effectively recognized by the native and adaptive immune systems. Therefore, the synthesis of new Kdo derivatives and neoglycoconjugates is highly important for the development of vaccines. This review highlights recent accomplishments related to α-glycosylations, β-glycosylations and C-glycosylations of Kdos and their application to the stereoselective synthesis of inner core oligosaccharides. 相似文献
99.
Yi Zheng Jingyu Yan Cuiyan Cao Yanfang Liu Dongping Yu Xinmiao Liang 《Journal of separation science》2023,46(18):2300368
Polysaccharides are widely distributed in natural sources from monocytic microorganisms to higher animals, and are found in a variety of biological activities in recent decades. Natural polysaccharides have the characteristics of large molecular weight, diverse composition, and complex structure, so their purification and structural analysis are difficult issues in research. Chromatography as a powerful separation technique, plays an irreplaceable role in the separation and structural analysis of natural polysaccharides, especially in the purification of polysaccharides, the separation of hydrolysates, and the analysis of monosaccharide composition. The separation mechanisms and application of different chromatographic methods in the studies of polysaccharides were summarized in this review. Moreover, the advantages and drawbacks of various chromatography methods were discussed as well. 相似文献
100.
Manuel Mönnich Dr. Steffen Eller Theodoros Karagiannis Lukas Perkams Thomas Luber Dr. Dimitri Ott Dr. Mathäus Niemietz Dr. Joanna Hoffman Janika Walcher Lukas Berger Dr. Matthias Pischl Markus Weishaupt Cathrin Wirkner Prof. Rachel G. Lichtenstein Prof. Carlo Unverzagt 《Angewandte Chemie (International ed. in English)》2016,55(35):10487-10492
The occurrence of N‐glycans with a bisecting GlcNAc modification on glycoproteins has many implications in developmental and immune biology. However, these particular N‐glycans are difficult to obtain either from nature or through synthesis. We have developed a flexible and general method for synthesizing bisected N‐glycans of the complex type by employing modular TFAc‐protected donors for all antennae. The TFAc‐protected N‐glycans are suitable for the late introduction of a bisecting GlcNAc. This integrated strategy permits for the first time the use of a single approach for multiantennary N‐glycans as well as their bisected derivatives via imidates, with unprecedented yields even in a one‐pot double glycosylation. With this new method, rare N‐glycans of the bisected type can be obtained readily, thereby providing defined tools to decipher the biological roles of bisecting GlcNAc modifications. 相似文献