| 1. |
- Auman, Dirk, et al.
(författare)
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Peroxy Intermediate Drives Carbon Bond Activation in the Dioxygenase AsqJ
- 2022
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 144:34, s. 15622-15632
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Tidskriftsartikel (refereegranskat)abstract
- Dioxygenases catalyze stereoselective oxygen atom transfer in metabolic pathways of biological, industrial, and pharmaceutical importance, but their precise chemical principles remain controversial. The α-ketoglutarate (αKG)-dependent dioxygenase AsqJ synthesizes biomedically active quinolone alkaloids via desaturation and subsequent epoxidation of a carbon–carbon bond in the cyclopeptin substrate. Here, we combine high-resolution X-ray crystallography with enzyme engineering, quantum-classical (QM/MM) simulations, and biochemical assays to describe a peroxidic intermediate that bridges the substrate and active site metal ion in AsqJ. Homolytic cleavage of this moiety during substrate epoxidation generates an activated high-valent ferryl (FeIV = O) species that mediates the next catalytic cycle, possibly without the consumption of the metabolically valuable αKG cosubstrate. Our combined findings provide an important understanding of chemical bond activation principles in complex enzymatic reaction networks and molecular mechanisms of dioxygenases.
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| 2. |
- Dorst, Kevin M., 1992-
(författare)
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Deciphering Carbohydrate Structure : From NMR Chemical Shifts to Conformational Analysis
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Carbohydrates are ubiquitous in nature and exhibit a multitude of roles. Besides nucleic and amino acids, they can be regarded as the third alphabet of life. They are used as energy source to fuel the cells, as structural building blocks and play a key role in cellular recognition processes. Compared to the other two groups of biomacromolecules, carbohydrates display a higher level of structural complexity by virtue of the number of individual monosaccharide building blocks, as well as the greater number of possibilities of connecting them and additional modifications. This renders a high information content and a good understanding of the structure-function relationship of glycans is important, since the presence or absence of specific structures can make the difference between health and disease.Carbohydrate structures can be characterized and studied by NMR spectroscopy at the atomic level. This process is time-consuming and error-prone, due to the narrow spectral window, in which most carbohydrate resonances are located leading to severe spectral overlap. Computer programs have been developed, aiding this process. This thesis investigates the quality of prediction of NMR chemical shifts of glycopeptides, highly branched oligosaccharide structures and those bearing a non-natural organic aglycone at the reducing end, as well as the automated determination of primary carbohydrate structures from unassigned NMR spectroscopic data thereof. Novel developments of the CASPER program are highlighted.The three-dimensional structure of carbohydrates plays an important role during carbohydrate-protein interactions. This thesis investigates the conformational preferences and dynamics of glycan structures ranging from di- to tetrasaccharides. A particular focus lies on the measurement of transglycosidic 3JCH coupling constants by NMR. Furthermore, the experimental spectroscopic data is compared to results from MD simulations.Synthetic carbohydrate chemistry has a strong focus on stereoselective C−O bond formation for the synthesis of oligo- and polysaccharides. Each glycosylation reaction can produce two stereoisomeric structures. To date, the mechanistic pathway of glycosylation reactions is still not fully understood, since many different parameters influence the stereoselectivity. A combined experimental and computational study exploring the role of the solvent is presented and a linear correlation of the selectivity with a solvatochromic parameter for the polarizability of the solvent was found.
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| 3. |
- Dorst, Kevin, 1992-, et al.
(författare)
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On the influence of solvent on the stereoselectivity of glycosylation reactions
- 2024
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Ingår i: Carbohydrate Research. - 0008-6215 .- 1873-426X. ; 535
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Tidskriftsartikel (refereegranskat)abstract
- Methodology development in carbohydrate chemistry entails the stereoselective formation of C-O bonds as a key step in the synthesis of oligo- and polysaccharides. The anomeric selectivity of a glycosylation reaction is affected by a multitude of parameters, such as the nature of the donor and acceptor, activator/promotor system, temperature and solvent. The influence of different solvents on the stereoselective outcome of glycosylation reactions employing thioglucopyranosides as glycosyl donors with a non-participating protecting group at position 2 has been studied. A large change in selectivity as a function of solvent was observed and a correlation between selectivity and the Kamlet-Taft solvent parameter pi* was found. Furthermore, molecular modeling using density functional theory methodology was conducted to decipher the role of the solvent and possible reaction pathways were investigated.
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