Biomedical subjects
Publications and source records attributed to Leendert J van den Bos.
A facile synthesis route toward beta-linked mannuronic acid oligomers using the corresponding 1-thiomannuronic acid esters in combination with the Ph2SO/Tf2O or NIS/TMSOTf reagent combinations is presented. The presence of the remotely attached carboxylic ester sufficiently influences the electronic environment to allow good to excellent beta-selectivities.
A historical overview is presented on stereo-directing effects of cis- and trans-fused diol protective groups used on both donor and acceptor glycosides. Attention is focused on the use of cyclic carbonates and carbamates, diacetals and acetals and finally the special case of 1,2-O-orthoesters and 1,2-O-cyanoalkylidene functionalised residues.
A variety of thioglycosides are chemoselectively hydrolyzed to the corresponding 1-hydroxy glycosides using equimolar amounts of NIS/TFA as promoter systems.
This tutorial review surveys the use of thioglycosides in the development of sequential glycosylation methodologies, with a focus on chemoselective, orthogonal and iterative glycosylation strategies reported since the beginning of this century. Both fundamental aspects of glycosidic bond formation and ingenious state-of-the-art methodologies are presented.
The chemo- and regioselective TEMPO/BAIB-mediated oxidation of 2,6- and 3,6-dihydroxy 1-thio glycopyranosides to the corresponding 1-thio uronic acid lactones is described. These locked 1-thio glycuronides can directly be used as donors in glycosidation reactions using the Ph(2)SO/Tf(2)O reagent system. Alternatively, selective opening of the lactone bridge liberates a hydroxyl function for ensuing glycosylations.
[reaction: see text] Partially protected thioglycuronic acids are prepared efficiently by chemo- and regioselective oxidation of the corresponding thioglycosides using the TEMPO/BAIB reagent combination. After esterification, the thioglycuronic acids proved to be useful as both donor and acceptor in sulfonium-mediated condensations toward acidic di- and trisaccharides.
A tethered nucleophilic substitution strategy for the stereoselective introduction of axially oriented amino functions on suitably protected gluco- and mannopyranosides is presented. The obtained oxazine is a versatile building block, which after some manipulation, could be used in the construction of highly functionalised oligosaccharides.
[reaction: see text] A novel sequential glycosylation procedure is described that combines the use of 1-hydroxyl and thiodonors. The Ph(2)SO/Tf(2)O-mediated dehydrative condensation of 1-hydroxyl donors with thioglycosides affords in good yield the thiodisaccharides, which in turn can be activated by the same activator system to furnish trisaccharides. The alpha-Gal epitope and a hyaluronan trisaccharide were efficiently assembled in a one-pot procedure.