From chitin to bioactive chitooligosaccharides and conjugates: access to lipochitooligosaccharides and the TMG-chitotriomycin

The direct and chemoselective N-transacylation of peracetylated chitooligosaccharides (COSs), readily obtained from chitin, to give per-N-trifluoroacetyl derivatives offers an attractive route to size-defined COSs and derived glycoconjugates. It involves the use of various acceptor building blocks and trifluoromethyl oxazoline dimer donors prepared with efficiency and highly reactive in 1,2-trans glycosylation reactions. This method was applied to the preparation of the important symbiotic glycolipids which are highly active on plants and to the TMG-chitotriomycin, a potent and specific inhibitor of insect, fungal, and bacterial N-acetylglucosaminidases.

Automated solution-phase synthesis of oligosaccharides via iterative electrochemical assembly of thioglycosides

A new iterative one-pot sequential method for the solution-phase synthesis of oligosaccharides has been devised on the basis of the electrochemical oxidation of a propagating thioglycoside terminus to generate the corresponding triflate, followed by the reaction with a thioglycoside building block having a free hydroxyl group. A practical automated synthesizer was developed for the method and was effectively used for assembling up to six thioglycoside building blocks to synthesize partial structures of poly-β-D-(1-6)-N-acetylglucosamine.

Comparison of the armed/disarmed building blocks of the D-gluco and D-glucosamino series in the context of chemoselective oligosaccharide synthesis

A very elegant Fraser-Reid armed-disarmed approach recently expanded to the building blocks of the superarmed and superdisarmed series shows very high utility in chemoselective oligosaccharide synthesis. Although a number of studies dedicated to the chemoselective activation of 2-amino-2-deoxysugars have emerged, little remains known about how the reactivity of the armed/disarmed building blocks of the neutral sugars directly compares to that of their 2-aminosugar counterparts. A preliminary study of this comparative reactivity is presented.

Electrochemical generation of glycosyl triflate pools

Glycosyl triflates, which serve as important intermediates in glycosylation reactions, were generated and accumulated by the low-temperature electrochemical oxidation of thioglycosides such as thioglucosides, thiogalactosides, and thiomannosides in the presence of tetrabutylammonium triflate (Bu(4)NOTf) as a supporting electrolyte. Thus-obtained solutions of glycosyl triflates (glycosyl triflate pools) were characterized by low-temperature NMR measurements. The thermal stability of glycosyl triflates and their reactions with glycosyl acceptors were also examined.

Recent trends in the synthesis of O-glycosides of 2-amino-2-deoxysugars

The discovery of new methods for stereoselective glycoside synthesis and convergent oligosaccharide assembly has been critical for the area of glycosciences. At the heart of this account is the discussion of the approaches for stereoselective synthesis of glycosides of 2-amino-2-deoxysugars that have emerged during the past two decades. The introductory part provides general background information and describes the key features and challenges for the synthesis of this class of compounds. Subsequently, major approaches to the synthesis of 2-amino-2-deoxyglycosides are categorized and discussed. Each subsection elaborates on the introduction (or protection) of the amino functionality, synthesis of glycosyl donors by introduction of a suitable leaving group, and glycosidation. Wherever applicable, the deprotection of a temporary amino group substituent and the conversion onto the natural acetamido functionality is described. The conclusions part evaluates the current standing in the field and provides a perspective for future developments.