Non-enzymatic Stereoselective S-glycosylation of Polypeptides and Proteins

2020 ◽  
Author(s):  
Dawen Niu ◽  
Li-Qiang Wan ◽  
Xia Zhang ◽  
Shi-Yang Xu ◽  
Rong Shi ◽  
...  
Keyword(s):  
Reaction Mechanism ◽  
Ambient Temperature ◽  
Functional Group ◽  
Aqueous Media ◽  
Experimental Studies ◽  
Powerful Technique ◽  
Glycosidic Bonds ◽  
Radical Processes ◽  
Glycosylation Reaction ◽  
Enzymatic Glycosylation

Abstract Glycosylation (1-4) is an essential and powerful technique that Nature employs to regulate the properties and functions of proteins and polypeptides. Our capacity to emulate Nature’s power, however, is limited by the methods available (5) to perform glycosylation on these complex biomolecules. So far, very few glycosylation reactions could operate under the conditions tolerated by biomolecules (e.g., aqueous media, mild pH, and ambient temperature), and the need to install glycosyl groups in a stereo-controlled fashion poses additional, significant challenges. Here we report a non-enzymatic glycosylation reaction that builds axial S-glycosidic bonds under biorelevant conditions. Our strategy exploits the exceptional functional group tolerance of radical processes, and is enabled by the design and use of allyl glycosyl sulfones as precursors to glycosyl radicals. Our method could introduce a variety of glycosyl units to the cysteine residues of polypeptides in a highly selective fashion. The power of this method is further demonstrated in the direct glycosylation of bioexpressed proteins. Computational and experimental studies provide insights into the reaction mechanism.

scholarly journals The influence of acceptor nucleophilicity on the glycosylation reaction mechanism

2017 ◽  
Vol 8 (3) ◽  
pp. 1867-1875 ◽  
Author(s):  
S. van der Vorm ◽  
T. Hansen ◽  
H. S. Overkleeft ◽  
G. A. van der Marel ◽  
J. D. C. Codée
Keyword(s):  
Reaction Mechanism ◽  
Systematic Study ◽  
Glycosylation Reaction

The acceptor dependence on the glycosylation stereoselectivity is revealed by a systematic study employing model acceptors of gradually changing nucleophilicity.

scholarly journals Transition-Metal-Free Boryl Substitution Using Silylboranes and Alkoxy Bases

Synlett ◽  
2017 ◽  
Vol 28 (11) ◽  
pp. 1258-1267 ◽  
Author(s):  
Hajime Ito ◽  
Eiji Yamamoto ◽  
Satoshi Maeda ◽  
Tetsuya Taketsugu
Keyword(s):  
Transition Metal ◽  
Functional Group ◽  
Experimental Studies ◽  
Transition Metal Catalysts ◽  
Alkyl Halides ◽  
Aryl Halides ◽  
Nucleophilic Attack ◽  
Important Class ◽  
Mechanistic Studies ◽  
Induced Reaction

Silylboranes are used as borylation reagents for organohalides in the presence of alkoxy bases without transition-metal catalysts. PhMe2Si–B(pin) reacts with a variety of aryl, alkenyl, and alkyl halides, including sterically hindered examples, to provide the corresponding organoboronates in good yields with high borylation/silylation ratios, showing good functional group compatibility. Halogenophilic attack of a silyl nucleophile on organohalides, and subsequent nucleophilic attack on the boron electrophile are identified to be crucial, based on the results of extensive theoretical and experimental studies. This boryl­ation reaction is further applied to the first direct dimesitylboryl (BMes2) substitution of aryl halides using Ph2MeSi–BMes2 and Na(O-t-Bu), affording aryldimesitylboranes, which are regarded as an important class of compounds for organic materials.1 Introduction2 Boryl Substitution of Organohalides with PhMe2Si–B(pin)/Alkoxy Bases3 Mechanistic Investigations4 DFT Mechanistic Studies Using an Artificial Force Induced Reaction (AFIR) Method5 Dimesitylboryl Substitution of Aryl Halides with Ph2MeSi–BMes2/Na(O-t-Bu)6 Conclusion

scholarly journals Prevention of UVI Precipitation in Alkaline Aqueous Solutions by the Siderophore Desferrioxamine B

2020 ◽  
Author(s):  
Matthew Kirby ◽  
Jason Louis Sonnenberg ◽  
Jonathan S. Watson ◽  
Dominik Weiss
Keyword(s):  
Functional Group ◽  
Experimental Studies ◽  
Binding Mode ◽  
Batch Experiments ◽  
Desferrioxamine B ◽  
Waste Storage ◽  
Contaminant Sources ◽  
Waste Repositories ◽  
Saline Solutions ◽  
The Impact

<p>In alkaline and saline solutions, uranium VI (U<sup>VI</sup>)<sup> </sup>forms uranyl salts, limiting its mobility in leachates released from nuclear waste repositories into groundwater. However, recent experimental and computational work suggested that natural organic molecules widely present in groundwater such as siderophores could potentially prevent solid precipitation because of the formation of stable UVI-siderophore complexes. It is important we assess the impact of siderophores on aqueous U<sup>VI</sup> chemistry as they could mobilise U<sup>VI </sup>from contaminated land and radioactive waste storage and disposal sites. Here we test this hypothesis by combining for the first time experimental studies on uranium precipitation in alkaline pH in the presence of desferrioxamine B (DFOB) and electron structure method calculation of uranyl – hydroxamate complexes to assess their stability. Stirred batch experiments containing 0 to 420 µM DFOB, 42 µM U<sup>VI</sup> and 0.1 M NaCl were conducted at pH 11.5. DFT was employed to explore the relative stability of different U<sup>VI</sup>-hydroxamate complexes, representative of the local binding mode of DFOB. During the stirred batch experiments, 5%, 11-12%, 41-53%, 95-96% and 100% of U<sup>VI</sup> passes through the filter membranes (0.2-1 µm pore diameter) after 24 hours when 0, 4.2, 42, 130 and 420 µM DFOB was added to solution. The DFT results suggest one hydroxamate functional group is most likely to complex with U<sup>VI</sup> with ∆<sub>r</sub>G calculated as +3 kJ/mol and -9 kJ/mol for [UO<sub>2</sub>(OH)<sub>3</sub>(L<sub>mono</sub>)]<sup>2- </sup>and [UO<sub>2</sub>(OH)<sub>2</sub>(L)]<sup>-</sup> respectively. Conversion of the experimentally derived log β (-1.2 ± 0.3) through the equation ∆<sub>r</sub>G = -2.303RTlogβ provides ∆<sub>r</sub>G of +7 kJ/mol, similar to the ∆<sub>r</sub>G of these two complexes. The results of our study confirm that U<sup>VI</sup> precipitation could be hindered by the formation of a DFOB complex with U<sup>VI</sup> complexation through a single hydroxamate functional group as a likely mechanism. These results highlight the mobilising effect siderophores have on U<sup>VI</sup> from contaminant sources and need to be incorporated in environmental risk assessment studies.</p>

Development of calix[4]arenes modified at their narrow- and wider-rims as potential metal ions sensor layers for microcantilever sensors: further studies

2021 ◽  
Author(s):  
Paris E. Georghiou ◽  
Shofiur Rahman ◽  
Yousif Assiri ◽  
Gopi Kishore Valluru ◽  
Melita Menelaou ◽  
...  
Keyword(s):  
Metal Ions ◽  
Metal Ion ◽  
Computational Study ◽  
Aqueous Media ◽  
Experimental Studies ◽  
Ionic Species ◽  
Alkoxy Group ◽  
Self Assembled Monolayers ◽  
Microcantilever Sensors ◽  
Assembled Monolayers

The development of a microcantilever (MCL) sensing device capable of simultaneously detecting several metal ionic species in aqueous media with low limits of detection requires a variety of sensing layers which are ion-specific. Calix[4]arenes are robust molecules which can be easily modified and have been extensively studied for their ion binding properties. They are also capable of forming self-assembled monolayers (SAMs) onto the gold layers of MCLs and are capable of detecting various metal ions with different anionic counterions in aqueous solutions. In this paper we report on the effect of the alkoxy group in the narrow rim [O-(alkoxycarbonyl)methoxy] substituents of bimodal calix[4]arenes which have been used as metal ion MCL sensing layers, using classical solution state experimental studies. A DFT computational study to compare the experimental results with several metal ions is also reported herein.

scholarly journals Environmental conditions alter successional trajectories on an ephemeral resource: a field experiment with beetles in dead wood

Oecologia ◽  
2020 ◽  
Vol 194 (1-2) ◽  
pp. 205-219
Author(s):  
Ole Petter Laksforsmo Vindstad ◽  
Tone Birkemoe ◽  
Rolf Anker Ims ◽  
Anne Sverdrup-Thygeson
Keyword(s):  
Species Richness ◽  
Community Structure ◽  
Ambient Temperature ◽  
Dead Wood ◽  
Species Turnover ◽  
Experimental Studies ◽  
Developmental Rate ◽  
Fungal Community Composition ◽  
Species Richness And Abundance ◽  
Ephemeral Resources

Abstract Successional processes can be observed for many organisms and resources, but most studies of succession have focused on plants. A general framework has been proposed, advocating that successional patterns in species turnover are predominantly driven by competition, dispersal or abiotic limitation, and that the patterning of species accumulation over time gives clues to which process is most influential in a given system. We applied this framework to succession in communities of wood-living beetles, utilizing ephemeral resources in the form of 60 experimentally created dead aspen high stumps. High stumps were created at sun-exposed sites (high ambient temperature; favourable abiotic conditions) and shaded sites (low ambient temperature; abiotically limiting conditions). The sites were intermixed, ensuring similar dispersal opportunities. Beetle species richness and abundance were monitored with flight interception traps over four consecutive years. Consistent with predictions from the tested framework, several beetle functional groups accumulated species more slowly at the unfavourable shaded sites than at the favourable exposed sites. Species richness at the exposed sites increased rapidly to a plateau, consistent with a limiting effect of competition on community development. Similar results were obtained for beetle abundance and community structure. Part of the variance in beetle community structure was jointly explained by habitat and fungal community composition, suggesting that differences in the composition and developmental rate of fungal communities in the two habitats contributed to the observed patterns. Targeted experimental studies are now required to decisively establish what processes underlie the contrasting successional trajectories in the two environments.

Highly effective Brønsted base/lewis acid cooperative catalysis: a new Cd metal–organic framework for the synthesis of Hantzsch 1,4-DHPs at ambient temperature

2017 ◽  
Vol 41 (24) ◽  
pp. 15475-15484 ◽  
Author(s):  
Farzaneh Rouhani ◽  
Ali Morsali
Keyword(s):  
Ambient Temperature ◽  
Lewis Acid ◽  
Functional Group ◽  
Metal Organic Framework ◽  
Cooperative Catalysis ◽  
Highly Effective ◽  
Metal Organic ◽  
Brønsted Base ◽  
Organic Framework

A new 3D metal–organic framework {[Cd3(BDC)3(OPP)(DMF)2]·2DMA}n (TMU-33) has been synthesized. The performance of the imine functional group of the OPP ligand as a Brønsted base and open Cd site as a Lewis acid in this framework was investigated as cooperative catalyst.

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