1,720,983 research outputs found
Boron Chemistry
No full textA basic overview of the essential aspects of the very rich boron chemistry is discussed to give elements for the comprehension of the structural behavior and chemical properties of boron-containing molecules. Some introductory elements are given on the peculiar chemical properties shown by boron, which derive from its electronic configuration; bonding orbitals and electronegativity are fundamental to understand boron behavior. The structural complexity deriving from these properties, which results in a variety of structures of elemental boron and boron derivatives, is subsequently introduced, followed by an outline of the main classes of boron-containing compounds. This overview begins with inorganic boron derivatives, followed by carbon-containing compounds, and, finally, organic boron compounds are also considered
A versatile synthesis of αGalCer and its analogues exploiting a cyclic carbonate as phytosphingosine 3,4-diol protecting group
Full text linkA convenient synthetic strategy to αGalCer and some relevant analogues by using a handily protected phytosphingosine is reported here. The conversion of the phytosphingosine amino group to azide and the protection of 3,4-diol as cyclic carbonate group, cleavable in mild basic conditions but resistant to acidic treatment, afforded quickly an excellent glycosyl acceptor. Its glycosylation with a proper galactosyl donor, gave a versatile intermediate in high yield and excellent stereoselectivity. To demonstrate the potentiality of the intermediate, three immunologically relevant compounds were chosen as model targets: αGalCer, dansyl alpha-galactosylceramide and 7DW8-5. These products were easily obtained in few steps and high yields to validate the synthetic route
Unusual promoters and leaving groups in glycosylation reactions: The evolution of carbohydrate synthesis
No full textGlycosylation is the key reaction by which our body can produce and modify carbohydrates and their conjugates which are molecules essential for life. The study of the diversity of their functions is a current and ever-expanding topic that requires the ability to provide pure saccharides quickly, efficiently and in a controlled way which can be achieved by chemical synthesis. Although the influence of the donor and the promoter on the outcome of a glycosylation reaction is well documented, the search for new methodologies and new promoters/activators is constantly expanding. In this review, after an introduction dealing with well-known glycosylation strategies, we describe the most recent advances in terms of the use of innovative approaches, focalizing the study on new promoters and leaving groups exploited in the last ten years
Exploring the pharmaceutical potential of ammonium organotrifluoroborate functional group: Comprehensive chemical, metabolic, and plasma stability evaluation
No full text: Boronated carbohydrate derivatives have good potential for targeting malignant cells in Boron Neutron Capture Therapy (BNCT) due to their preferential glucose uptake. In particular, with the introduction of the ammonium trifluoroborate moiety, boronated sugars can function as both BNCT agents and Positron Emission Tomography (PET) tracers. Their 18F radiolabeling allows real-time tracking of biodistribution. This study evaluates the chemical, metabolic, and plasma stability of ammonium trifluoroborates for pharmaceutical purposes using LC-HRMS, presenting stability data under various conditions -acidic, basic, pseudophysiological, and oxidative- and highlighting degradation products and mechanisms. The data are supported by 1H NMR and 19F NMR. Metabolic and plasma stabilities, along with preliminary toxicological data (MTT assays), are also provided to better predict the clinical applicability of these compounds
2,3-Carbamate mannosamine glycosyl donors in glycosylation reactions of diacetone-d-glucose. An experimental and theoretical study
No full textThe role of the cyclic 2,3-N,O-carbamate protecting group in directing the selectivity of mannosylation reactions of diacetone-D-glucose, promoted by BSP/Tf2O via a-triflate intermediates, has been investigated through a combined computational and experimental approach. DFT calculations were used to locate the transition states leading to the alpha or beta anomers. These data indicate the preferential formation of the beta-adduct with mannosyl donors either equipped with the 4,6-O-benzylidene protection or without it. The synthetic results confirmed this preference, showing in both cases an alpha/beta selectivity of 4:6. This highlights a role for the 2,3-N,O-carbamate in sharp contrast with what described in the case of 2,3-O-carbonate mannosyl donors
Anomeric sugar boronic acid analogues as potential agents for boron neutron capture therapy
No full textAn efficient and concise synthesis of α-galactosylceramide
No full textA concise and stereoselective synthesis of α-GalCer is described. The key features of the synthetic strategy are the use of a phytosphingosine in which the amine is masked as trichlorophthalimide, the diol as an isopropylidene acetal, and a galactosyl donor protected as a 4,6-benzylidene to improve the α selectivity of the glycosylation reaction. The pattern of protecting groups on the donor and the acceptor have proven to give an excellent match of reactivity allowing the glycosylation reaction to take place stereoselectively. The overall synthesis allowed to achieve α-GalCer in good yields and few steps
Trifluoromethyl Ketone Galactose Catalyst for Asymmetric Epoxidation: Experimental and Theoretical Model
No full textSince the introduction of the Shi catalyst, the organocatalytic epoxidation of olefins has become an area of continued research interest. To explore the possibility of enhancing the efficiency and stability of the catalyst, the synthesis of a galactose-derived trifluoromethyl ketone, and its use for stereoselective epoxidation reaction that exploits a transitory dioxirane as active species are herein reported. The trifluoromethyl ketone was built on the C6 of a protected d-galactopyranose. The organocatalyst was obtained smoothly in a few steps, and when utilized for stereoselective epoxidation exhibited excellent stability as no chemical alterations were observed during the reaction. The stereoselectivity, although sometimes moderate, appears surprisingly high considering the conformational freedom of the trifluoromethyl ketone moiety. DFT calculations were performed to investigate the interactions involved in regulating the observed selectivities. Moreover, a new mnemonic model has been developed to serve as a fast-predicting tool for epoxidation of new substrates
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