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Selected Publication:

Pokorny, B; Kosma, P.
(2015): Scope and Limitations of 3-Iodo-Kdo Fluoride-Based Glycosylation Chemistry using N-Acetyl Glucosamine Acceptors
CHEMISTRYOPEN. 2015; 4(6): 722-728. FullText FullText_BOKU

The ketosidic linkage of 3-deoxy-D-manno-octulosonic acid (Kdo) to lipid A constitutes a general structural feature of the bacterial lipopolysaccharide core. Glycosylation reactions of Kdo donors, however, are challenging due to the absence of a directing group at C-3 and elimination reactions resulting in low yields and anomeric selectivities of the glycosides. While 3-iodo-Kdo fluoride donors showed excellent glycosyl donor properties for the assembly of Kdo oligomers, glycosylation of N-acetyl-glucosamine derivatives was not straightforward. Specifically, oxazoline formation of a beta-anomeric methyl glycoside, as well as iodonium ion transfer to an allylic aglycon was found. In addition, dehalogenation of the directing group by hydrogen atom transfer proved to be incompatible with free hydroxyl groups next to benzyl groups. In contrast, glycosylation of a suitably protected methyl 2-acetamido-2-deoxy-alpha-dglucopyranoside derivative and subsequent deiodination proceeded in excellent yields and alpha-specificity, and allowed for subsequent 4-O-phosphorylation. This way, the disaccharides alpha-Kdo-(2 -> 6)-alpha-GlcNAcOMe and alpha-Kdo-(2 -> 6)-alpha-GlcNAcOMe-4-phosphate were obtained in good overall yields.
Authors BOKU Wien:
Kosma Paul
Pokorny Barbara

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