Scope and Limitations of 3‐Iodo‐Kdo Fluoride‐Based Glycosylation Chemistry using N‐Acetyl Glucosamine Acceptors

ChemistryOpen

Barbara Pokorny¹ 

[1] Department of Chemistry, University of Natural Resources and Life Sciences-Vienna, Vienna, Austria

关键词: glycosylation;    hydrogen transfer;    iodonium;    Kdo;    lipopolysaccharide;   

DOI  :  10.1002/open.201500126

来源: Wiley

【 摘 要 】

Abstract

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 β-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-α-d-glucopyranoside derivative and subsequent deiodination proceeded in excellent yields and α-specificity, and allowed for subsequent 4-O-phosphorylation. This way, the disaccharides α-Kdo-(2→6)-α-GlcNAcOMe and α-Kdo-(2→6)-α-GlcNAcOMe-4-phosphate were obtained in good overall yields.

【 授权许可】

CC BY   
© 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

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