An Expeditious Synthesis of N-acetylneuraminic acid α-C-glycosyl derivatives ('α-C-Glycosides') from the Anomeric Acetates

The reductive metallation of the readily available peracetylated derivatives of methyl N-acetylneuraminate 3a and 3b by samarium diiodide without any additive generates the corresponding anomeric samarium(III) organometallics. These intermediates react efficiently with carbonyl compounds under Barbier conditions, providing a fast synthesis of C-ketosides. The α- and β-acetates are equally effective, and excellent yields are obtained for coupling with cyclic ketones. The procedure has been conveniently applied to the synthesis of a C-ketoside of N-acetylneuraminic acid with an attached linker, ready to use as a building block in the elaboration of multivalent biological probes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)