A major challenge in the chemical synthesis and derivatization of natural product polysaccharides is the ability to conduct chemical glycosylation reactions with high alpha or beta stereoselectivity at the anomeric center. The issue of stereoselectivity is compounded with 2-deoxy sugar substrates, which lack a handle at the C2 position for anchimeric assistance and are highly unstable to elimination when converted to active intermediates. To mitigate these drawbacks, our group has been exploring approaches to deoxy sugar glycosylation where the stereochemical outcome of the reaction is controlled entirely by the promoter system, as a gateway to the synthesis of carbohydrate natural products. Arugomycin (AGM) is a 2-deoxy sugar anthracycline natural product isolated from Streptomyces violaceochromogenes that has weak bactericidal activity. The tetrasaccharide fragment of AGM is of interest to the Bennett lab as a model system to expand our alpha-selective reagent-controlled glycosylation methodology to facilitate couplings of 2-deoxy sugars. This method utilizes a third-generation promoter system of an aryl cyclopropene thione and oxalyl bromide to convert shelf-stable hemiacetals to active beta-linked glycosyl donors in situ via cyclopropenium cation activation, which can react stereoselectively with nucleophilic acceptors to give alpha-linked products. Our application of this technology to the convergent synthesis of the AGM tetrasaccharide from commercially available L-Fucose will be presented.

Reagent-controlled alpha-selective glycosylations of 2-deoxy sugars: convergent synthesis of the Arugomycin tetrasaccharide

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.