Journal
JOURNAL OF ORGANIC CHEMISTRY
Volume 83, Issue 8, Pages 4581-4597Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.joc.8b00340
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Funding
- Okinawa Institute of Science and Technology Graduate University
- MEXT/JSPS (Japan) [26105757]
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C-Glycoside derivatives are found in pharmaceuticals, glycoconjugates, probes, and other functional molecules. Thus, C-glycosidation of unprotected carbohydrates is of interest. Here the development of C-glycosidation reactions of unprotected di- and trisaccharide aldopyranoses with various ketones is reported. The reactions were performed using catalyst systems composed of pyrrolidine and boric acid under mild conditions. Carbohydrates used for the C-glycosidation included lactose, maltose, cellobiose, 3'-sialyllactose, 6'-sialyllactose, and maltotriose. Using ketones with functional groups, C-glycosides ketones bearing the functional groups were obtained. The pyrolidine-boric acid catalysis conditions did not alter the stereochemistry of non-C-C bond formation positions of the carbohydrates and led to the formation of the C-glycosidation products with high diastereoselectivity. For the C-glycosidation of the carbohydrates under the pyrrolidine-boric acid-catalysis, the hydroxy group at the 6-position of the reacting aldopyranose was necessary to afford the product. Our analyses suggest that the carbohydrates form iminium ions with pyrrolidine and that boric acid forms B-O covalent bonds with the carbohydrates during the catalysis to forward the C-C bond formation.
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