PubMed Health⌕ Search

Biomedical subjects

Olof Ramström

Publications and source records attributed to Olof Ramström.

13 recordsLinked to original sources
PubMed2006

Glycosyldisulfides from dynamic combinatorial libraries as O-glycoside mimetics for plant and endogenous lectins: their reactivities in solid-phase and cell assays and conformational analysis by molecular dynamics simulations.

Dynamic combinatorial library design exploiting the thiol-disulfide exchange readily affords access to glycosyldisulfides. In order to reveal lectin-binding properties of this type of non-hydrolyzable sugar derivative, libraries originating from a mixture of common building blocks of natural glycans and thiocompounds were tested against three plant agglutinins with specificity to galactose, fucose or N-acetylgalactosamine, respectively, in a solid-phase assay. Extent of lectin binding to matrix-immobilized neoglycoprotein presenting the cognate sugar could be reduced, and evidence for dependence on type of carbohydrate was provided by dynamic deconvolution. Glycosyldisulfides also maintained activity in assays of increased physiological relevance, that is, using native tumor cells and also adding to the test panel an endogenous lectin (galectin-3) involved in tumor spread and cardiac dysfunction. N-Acetylgalactosamine was pinpointed as the most important building block of libraries for the human lectin and the digalactoside as most potent compound acting on the toxic mistletoe agglutinin which is closely related to the biohazard ricin. Because this glycosyldisulfide, which even surpasses lactose in inhibitory capacity, rivals thiodigalactoside as inhibitor, their degrees of intramolecular flexibility were comparatively analyzed by computational calculations. Molecular dynamics runs with explicit consideration of water molecules revealed a conspicuously high degree of potential for shape alterations by the disulfide's three-bond system at the interglycosidic linkage. The presented evidence defines glycosyldisulfides as biologically active ligands for lectins.

Binding Sites↗
PubMed2006

Stereospecific ester activation in nitrite-mediated carbohydrate epimerization.

[reaction: see text] The Lattrell-Dax method of nitrite-mediated substitution of carbohydrate triflates is an efficient method to generate structures of inverse configuration. In the present study, epimerization of gluco- and galactopyranoside derivatives to the corresponding allo- and gulopyranoside structures by triflation/nitrite treatment has been investigated. It was found that a neighboring ester group was essential for the reactivity of the nitrite-mediated triflate inversion. Furthermore, a good inversion yield also depended on the relative configuration of the neighboring ester group to the triflate. Only with the ester group in the equatorial position, whatever the configuration of the triflate, did the reaction proceed smoothly, whereas a neighboring axial ester group proved largely inefficient. The results were subsequently used to predict the inversion of glucopyranoside derivatives to the mannopyranoside epimers.

Carbohydrates↗
PubMed2006

Quartz crystal microbalance bioaffinity sensor for rapid identification of glycosyldisulfide lectin inhibitors from a dynamic combinatorial library.

Carbohydrate-lectin interactions were probed with dynamic combinatorial libraries, using the plant lectin Concanavalin A as target species. The dynamic combinatorial libraries were generated from a pool of thiol components through reversible thiol-disulfide interchange, and screened using a simple and efficient method based on a quartz crystal microbalance setup. It was found that dimers based on 1-thio- and 6-thio-mannose analogues were the most active inhibitors. Furthermore, the results clearly show that the 6-thio-mannose possess unique characteristics compared to its oxygen-containing counterpart.

Biosensing Techniques↗
PubMed2005

Solvent-dependent, kinetically controlled stereoselective synthesis of 3- and 4-thioglycosides.

Facile approaches to prepare 3- and 4-thioglycosides of the galacto, gulo, and gluco type from the parent triflates are presented. The dependencies of the solvent and the protecting group pattern, as well as the configuration of the neighboring and leaving groups, have been studied for these reactions. The results clearly show that the efficient stereoselective synthesis of methyl 3-thio-galactoside depends highly on the solvent and the nucleophile concentration.

Journal Article↗
PubMed2005

Redox-responsive and calcium-dependent switching of glycosyldisulfide interactions with Concanavalin A.

Glycosyldisulfides can interact efficiently with carbohydrate-binding entities. This has been shown for a range of thiosaccharide dimers when tested for their effects against the lectin Concanavalin A using a modified quartz crystal microbalance-technique. Contrary to the thiosaccharide monomers, showing no significant binding up to 10 mM, several of the dimers showed IC(50)-values in the low millimolar range. Three of the glycosyldisulfides tested also displayed very high positive apparent cooperativity effects that were found to be both calcium-dependent and redox-responsive.

Calcium↗
PubMed2004

Study of real-time lectin-carbohydrate interactions on the surface of a quartz crystal microbalance.

A quartz crystal microbalance (QCM) biosensor system for lectin-carbohydrate interactions has been developed. Yeast mannan was immobilised on polystyrene-coated quartz crystals, and interactions tested with the lectin concanavalin A (Con A). The biosensor could be easily operated, where mannan immobilisation and all binding analyses were performed in real-time using a flow-through system. The apparent binding constant for yeast mannan to Con A was estimated to be 0.4 microM, well in accordance to reported literature values. In addition, the effective concentration values (EC50-values) for a series of mannose/mannoside ligands, acting as competitors to the mannan/Con A interaction, were determined to range from 0.18 to 5.3 mM, in good correlation with a related enzyme-labelled lectin assay (ELLA) protocol.

Biosensing Techniques↗
PubMed2004

Dynamic combinatorial carbohydrate libraries: probing the binding site of the concanavalin A lectin.

Dynamic combinatorial chemistry (DCC) has emerged as an efficient approach to receptor/ligand identification based on the generation of combinatorial libraries by reversible interconversion of the library constituents. In this study, the implementation of such libraries on carbohydrate-lectin interactions was examined with the plant lectin Concanavalin A as a target species. Dynamic carbohydrate libraries were generated from a pool of carbohydrate aldehydes and hydrazide linker/scaffold components through reversible acylhydrazone exchange, resulting in libraries containing up to 474 constituents. Dynamic deconvolution allowed the efficient identification of the structural features required for binding to Concanavalin A and the selection of a strong binder, a tritopic mannoside, showing an IC(50)-value of 22 microM.

Binding Sites↗
PubMed2003

Generation of bis-cationic heterocyclic inhibitors of Bacillus subtilis HPr kinase/phosphatase from a ditopic dynamic combinatorial library.

Ditopic dynamic combinatorial libraries were generated and screened toward inhibition of the bifunctional enzyme HPr kinase/phosphatase from Bacillus subtilis. The libraries were composed of all possible combinations resulting from the dynamic interconversion of 16 hydrazides and five monoaldehyde or dialdehyde building blocks, resulting in libraries containing up to 440 different constituents. Of all possible acyl hydrazones formed, active compounds containing two terminal cationic heterocyclic recognition groups separated by a spacer of appropriate structure could be rapidly identified using a dynamic deconvolution procedure. Thus, parallel testing of sublibraries where one specific component was excluded basically revealed all the essential components. A potent ditopic inhibitor, based on 2-aminobenzimidazole, was identified from the process.

Aldehydes↗
PubMed2002

Chemical biology of dynamic combinatorial libraries.

Dynamic combinatorial chemistry (DCC) is a recently introduced supramolecular approach to generate libraries of chemical compounds based on reversible exchange processes. The building elements are spontaneously and reversibly assembled to virtually encompass all possible combinations, allowing for simple one-step generation of complex libraries. The method has been applied to a variety of combinatorial systems, ranging from synthetic models to materials science and drug discovery, and enables the establishment of adaptive processes due to the dynamic interchange of the library constituents and its evolution toward the best fit to the target. In particular, it has the potential to become a useful tool in the direct screening of ligands to a chosen receptor without extensive prior knowledge of the site structure, and several biological systems have been targeted. In the vast field of glycoscience, the concept may find special perspective in response to the highly complex nature of carbohydrate-protein interactions. This chapter summarises studies that have been performed using DCC in biological systems, with special emphasis on glycoscience.

Carbohydrates↗
PubMed2002

Drug discovery by dynamic combinatorial libraries.

Dynamic combinatorial chemistry is a recently introduced supramolecular approach that uses self-assembly processes to generate libraries of chemical compounds. In contrast to the stepwise methodology of classical combinatorial techniques, dynamic combinatorial chemistry allows for the generation of libraries based on the continuous interconversion between the library constituents. Spontaneous assembly of the building blocks through reversible chemical reactions virtually encompasses all possible combinations, and allows the establishment of adaptive processes owing to the dynamic interchange of the library constituents. Addition of the target ligand or receptor creates a driving force that favours the formation of the best-binding constituent--a self-screening process that is capable, in principle, of accelerating the identification of lead compounds for drug discovery.

Combinatorial Chemistry Techniques↗