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The total synthesis of mixed-sequence alginate oligosaccharides, featuring both β-D-mannuronic acid (M) and α-L-guluronic acid (G), is reported for the first time. A set of GM, GMG, GMGM, GMGMG, GMGMGM, GMGMGMG, and GMGGMG alginates was assembled using GM building blocks, having a guluronic acid acceptor part and a mannuronic acid donor side to allow the fully stereoselective construction of the cis-glycosidic linkages. It was found that the nature of the reducing-end anomeric center, which is ten atoms away from the reacting alcohol group in the key disaccharide acceptor, had a tremendous effect on the efficiency with which the building blocks were united. This chiral center determines the overall shape of the acceptor and it is revealed that the conformational flexibility of the acceptor is an all-important factor in determining the outcome of a glycosylation reaction., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Lewis acid mediated substitution reactions using [D]triethylsilane as a nucleophile at the anomeric center of the four pentofuranoses, ribose, arabinose, xylose, and lyxose, all proceed with good to excellent stereoselectivity to provide the 1,2-cis adducts. To unravel the stereoelectronic effects underlying the striking stereoselectivity in these reactions we have mapped the energy landscapes of the complete conformational space of the oxocarbenium ions of the four pentofuranoses. The potential energy surface maps provide a detailed picture of the influence of the differently oriented substituents and their mutual interactions on the stability of the oxocarbenium ions and the maps can be used to account for the observed stereoselectivities of the addition reactions., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A high-end label: Cyclophellitol aziridine-type activity-based probes allow for ultra-sensitive visualization of mammalian β-glucosidases (GBA1, GBA2, GBA3, and LPH) as well as several non-mammalian β-glucosidases (see picture). These probes offer new ways to study β-exoglucosidases, and configurational isomers of the cyclophellitol aziridine core may give activity-based probes targeting other retaining glycosidase families., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)