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.

[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.

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The purification of heparin from offal is an old industrial process for which commercial recipes date back to 1922. Although chemical, chemoenzymatic, and biotechnological alternatives for this production method have been published in the academic literature, animal-tissue is still the sole source for commercial heparin production in industry. Heparin purification methods are closely guarded industrial secrets which are not available to the general (scientific) public. However by reviewing the academic and patent literature, we aim to provide a comprehensive overview of the general methods used in industry for the extraction of heparin from animal tissue.

Glycosylations of mannuronate ester donors proceed highly selectively to produce the 1,2-cis-linked products. We here forward a mechanistic rationale for this counterintuitive selectivity, based on the remote stereodirecting effect of the C5-carboxylate ester, which has been demonstrated using pyranosyl uronate ester devoid of ring substituents other than the C5- carboxylate ester. It is postulated that the C5-carboxylate ester prefers to occupy an axial position in the oxacarbenium intermediate, thereby favoring the formation of the (3)H4 half-chair over the (4)H3 conformer. Nucleophilic attack on the (3)H4 half-chair intermediate occurs in a beta-fashion, providing the 1,2-cis-mannuronates with excellent stereoselectivity. The potential of the mannuronate ester donors in the formation of the beta-mannosidic linkage has been capitalized upon in the construction of a mannuronic acid alginate pentamer using a convergent orthogonal glycosylation strategy.

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.

This Microreview covers some general strategies for the preparation of uronic acid residues and their incorporation into anionically charged oligosaccharides. Two distinct strategies can be recognized: (1) glycosylation followed by oxidation, and (2) oxidation of the monosaccharide building