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138 results on '"Khiar N"'

1. Surface modulation of single-walled carbon nanotubes for selective bacterial cell agglutination

Author

Romero-Ben E, Cid JJ, Assali M, Fernández-García E, Wellinger RE, and Khiar N

Subjects
Single wall Carbon Nanotubes, Carbohydrates, Bacterial Resistance, Antiadhesive Therapy, Multivalency. Aryl Diazonium Salts Chemistry, Medicine (General), R5-920
Abstract

Elena Romero-Ben,1 Juan José Cid,1 Mohyeddin Assali,1 Elisabeth Fernández-García,2 Ralf Erik Wellinger,2 Noureddine Khiar1 1Asymmetric Synthesis and Functional Nanosystems Group, Institute of Chemical Research-Universidad de Sevilla, Avda. Américo Vespucio, 41092 Seville, Spain; 2Genome Stability Department, Andalusian Center for Molecular Biology and Regenerative Medicine Centre, Universidad de Sevilla-CSIC, Avda. Américo Vespucio, 41092 Seville, Spain Background: Bacterial resistance to antibiotics is one of the biggest challenges facing medicine today. Anti-adhesive therapy, using inhibitors of bacterial adhesion to epithelial cells, one of the first stages of infection, is a promising approximation in this area. The size, shape, number of sugar and their placement are variables that have to be taken into account in order to develop multivalent systems able to inhibit the bacterial adhesion based on sugar-lectin interaction. Materials and methods: In the present work we report a modular approach for the synthesis of water-soluble 1D-carbon nanotube-sugar nanoconstructs, with the necessary flexibility to allow an efficient sugar-lectin interaction. The method is based on the reaction of aryl diazonium salts generated in situ from aniline-substituted mannose and lactose derivatives with single wall carbon nanotubes (SWCNTs) sidewalls. Results: Two hybrid nanosystems, I-II, exposing mannose or lactose and having a tetraethylene glycol spacer between the sugar and the nanotube sidewall were rapidly assembled and adequately characterized. The sweet nano-objects were then tested for their ability to agglutinate and selectively inhibit the growth of uropathogenic Escherichia coli. These studies have shown that nanosystem I, exposing mannose on the nanotube surface is able to agglutinate and to inhibit the bacterial growth unlike nano-objects II exposing lactose.Conclusion: The results reported constitute a proof of principle in using mannose-coated 1D-carbon nanotubes as antiadhesive drugs that compete for FimH binding and prevent the uropathogenic bacteria from adhering to the urothelial surface. Keywords: single-walled carbon nanotubes, carbohydrates, bacterial resistance, antiadhesive therapy, multivalency, aryl diazonium salts chemistry

Published
2019

3. General method for asymmetric synthesis of alpha-methylsulfinyl ketones: application to the synthesis of optically pure oxisuran and bioisosteres

Author

El Ouazzani, H., Khiar, N., Fernandez, I., and Alcudia, F.

Subjects
Ketones -- Analysis, Oxo compounds -- Analysis, Immunosuppressive agents -- Analysis, Biological sciences, Chemistry
Abstract

The first asymmetric synthesis of oxisuran and various related bioisosteres in optically pure form, where the pyridine ring has been replaced by another aromatic ring, is described. The synthesis of the sulfoxides proceeded using DAG methodology, a powerful approach for the synthesis of dialkyl chiral sulfoxides. Epimerization at sulfur was circumvented with the use of N,N-dimethylhydrazones, resulting in the complete inversion of chirality.

Published
1997

4. Asymmetric synthesis of alkane- and arenesulfinates of diacetone-D-glucose (DAG): an improved and general route to both enentiometrically pure sulfoxides

Author

Fernandez, I., Khiar, N., Llera, J. M., and Alcudia, F.

Subjects
Glucose -- Research, Grignard reagents -- Research, Sulfur compounds -- Research, Enantiomers -- Research, Biological sciences, Chemistry
Abstract

The reaction of diacetone-D-glucose (DAG) with sulfinyl chlorides were observed at -78 degrees Celsius using the bases i-Pr2NEt in toluene and Py in THF. The sulfinates were formed in high yields and purification was generally accomplished by column chromatography. The stereochemistry of the final sulfinate esters depends on the base used. Enantiomerically pure sulfoxides were obtained by reaction with several Grignard reagents.

Published
1992

8. 'Sulfolefin': a mixed sulfinamido-olefin ligand in enantioselective rhodium-catalyzed addition of arylboronic acids to trifluoromethyl ketones

Author

Valdivia Giménez, Victoria Esther, Fernández Fernández, Inmaculada, Khiar, N., and Universidad de Sevilla. Departamento de Química Orgánica y Farmacéutica

Subjects
Arylboronic acids, Enantioselective, Sulfinate esters, Rhodium-catalyzed, Catalyst precursors, Trifluoromethylketone, Asymmetric synthesis, Carbon-carbon bond
Abstract

Performing catalytic enantioselective carbon-carbon bond forming reactions, especially for the synthesis of tertiary carbinols, is one of the most challenging goals in modern asymmetric synthesis. Herein, we report an efficient enantioselective catalytic approach for the 1,2-addition of arylboronic acids to trifluoromethyl ketones affording tertiary trifluoromethyl-substituted alcohols with high yields and good enantioselectivities. The reported process uses as a catalyst precursor the shelf stable sulfinamido-olefin ligand 1, "sulfolefin", obtained on a multigram scale and in one step from a sugar derived sulfinate ester. Ministerio de Economía y Competitividad CTQ2010-21755-CO2-00

Published
2014

11. 'Sulfolefin': Highly modular mixed S/Olefin ligands for enantioselective Rh-catalyzed 1,4-addition

Author

Khiar, N., Salvador, Álvaro, Chelouan, Ahmed, Alcudia, Ana, Fernández Fernández, Inmaculada, and Universidad de Sevilla. Departamento de Química Orgánica y Farmacéutica

Subjects
Enantioselective, 1,4-addition, Boronic acid, Rapid optimization, Enantioselective catalysts, Step approximations, Synthetic design, Chiral centers, Sulfur atoms
Abstract

Reported is a single high yielding step approximation to mixed olefin/sulfinamide ligands enclosing a chiral sulfur atom as the sole chiral center. The synthetic design is validated by a rapid optimization of the substituent at the sulfinyl sulfur, and by the synthesis of an efficient, highly enantioselective catalyst for the Rh-catalyzed 1,4-addition of boronic acids to both, cyclic and acyclic olefins. Ministerio de Ciencia e Innovación CTQ2010-21755-CO2-00 Junta de Andalucía P07-FQM-2774

Published
2012

13. Chiral sulfur derivatives in the allylation of acyl hydrazones: C2-symmetric bis-sulfinamides as enhanced chiral organic promoters

Author

Fernández Fernández, Inmaculada, Alcudia, Ana, Gori, Beatrice, Valdivia Giménez, Victoria Esther, Recio, Rocío, García, María Victoria, Khiar, N., and Universidad de Sevilla. Departamento de Química Orgánica y Farmacéutica

Subjects
Allylations, Sulfur derivatives, Hydrazones, Key elements, Sulfinamides
Abstract

Monosulfinamides and C2-symmetric bis-sulfinamides are convenient neutral chiral promoters in the allylation of acyl hydrazones, the nature of the spacer and the substituent at the sulfinyl sulfur are key elements for the enantioselectivity of the process. Dirección General de Investigación Científica y Técnica CTQ2010-21755-C02-01 Dirección General de Investigación Científica y Técnica CTQ2010-21755-C02-02 Junta de Andalucía P06-FQM-01852 y P07-FQM-2774

Published
2010

40. General method for asymmetric synthesis of alpha-methylsulfinyl ketones: Application to the...

Author

Ouazzani, H. El and Khiar, N.

Subjects
*KETONES, *BIOSYNTHESIS
Abstract

Reports on the general method for synthesis of alpha-methylsulfinyl ketones. Application to the synthesis of oxisuran and bioisosteres; Diacetone D-glucose methodology; Reaction mechanisms; Configurational assignment; Determination of the optical purities of the beta-keto sulfoxides.

Published
1997
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41. A highly convergent synthesis of the tetragalactose moiety of the glycosyl phosphatidyl inositol...

Author

Khiar, N. and Martin-Lomas, M.

Subjects
*INOSITOL, *GLYCOPROTEIN synthesis, *BIOSYNTHESIS
Abstract

Reports on a highly convergent synthesis of the tetragalactose moiety of the glycosyl phosphatidyl inositol anchor of the variant surface glycoprotein of trypanosoma brucei. Reaction pathway; Vicinal proton-proton coupling constants; Reaction conditions.

Published
1995
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43. The Isopropylsulfinyl Group:  A Useful Chiral Controller for the Asymmetric Aziridination of Sulfinylimines and the Organocatalytic Allylation of Hydrazones

Author

Fernandez, I., Valdivia, V., Gori, B., Alcudia, F., Alvarez, E., and Khiar, N.

Abstract

A comparative study shows that the isopropylsulfinyl group for which an enantiodivergent and highly diastereoselective approach is reported behaves better than the tert-butylsulfinyl and p-tolylsulfinyl groups, both in terms of reactivity and stereoselectivity in the Corey−Chaykovsky reaction of chiral sulfinylimines and the organocatalytic allylation of acyl hydrazones.

Published
2005

44. Base-Catalyzed Inversion of Chiral Sulfur Centers. A Computational Study

Author

Balcells, D., Maseras, F., and Khiar, N.

Abstract

A theoretical study on the pyramidal inversion of the chiral sulfur compounds SO(X)(Me) (X = Cl, OMe, p-MePh) has been carried out by means of the DFT(Becke3LYP) method. Our results reveal that in the case of X = Cl, an organic tertiary amine such as NMe3 can catalyze the racemization. The base-catalyzed inversion of SO(Cl)(Me) is proposed as a feasible dynamic kinetic resolution mechanism for the synthesis of chiral sulfoxides by the DAG method.

Published
2004

45. NMR investigations of protein-carbohydrate interactions: refined three-dimensional structure of the complex between hevein and methyl beta-chitobioside.

Author

Asensio, J L, Cañada, F J, Bruix, M, González, C, Khiar, N, Rodríguez-Romero, A, and Jiménez-Barbero, J

Abstract

The specific interaction of hevein with GlcNAc-containing oligosaccharides has been analyzed by1H-NMR spectroscopy. The association constants for the binding of hevein to a variety of ligands have been estimated from1H-NMR titration experiments. The association constants increase in the order GlcNAc-alpha(1-->6)-Man < GlcNAc < benzyl-beta-GlcNAc < p-nitrophenyl-beta-GlcNAc < chitobiose < p-nitrophenyl-beta-chitobioside < methyl-beta-chitobioside < chitotriose. Entropy and enthalpy of binding for different complexes have been obtained from van't Hoff analysis. The driving force for the binding process is provided by a negative DeltaH0which is partially compensated by negative DeltaS0. These negative signs indicate that hydrogen bonding and van der Waals forces are the major interactions stabilizing the complex. NOESY NMR experiments in water solution provided 475 accurate protein proton-proton distance constraints after employing the MARDIGRAS program. In addition, 15 unambiguous protein/carbohydrate NOEs were detected. All the experimental constraints were used in a refinement protocol including restrained molecular dynamics in order to determine the highly refined solution conformation of this protein-carbohydrate complex. With regard to the NMR structure of the free protein, no important changes in the protein nOe's were observed, indicating that carbohydrate-induced conformational changes are small. The average backbone rmsd of the 20 refined structures was 0.055 nm, while the heavy atom rmsd was 0.116 nm. It can be deduced that both hydrogen bonds and van der Waals contacts confer stability to the complex. A comparison of the three-dimensional structure of hevein in solution to those reported for wheat germ agglutinin (WGA) and hevein itself in the solid state has also been performed. The polypeptide conformation has also been compared to the NMR-derived structure of a smaller antifungical peptide, Ac-AMP2.

Published
1998
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