Synthesis of L-Hexopyranosyl Fluorides Enabled by Radical Decarboxylative Fluorination: Assembly of a Pentasaccharide Repeating Unit Corresponding to Extracellular Polysaccharide S-88 Zhi Qiao, Dongwei Li, Jingru Gao, Zijiao Hou, Ningjie Yan, Ni Song, Peng Wang*, and Ming Li* Chin. J. Chem. 2023, 41, XXX—XXX. DOI: 10.1002/cjoc.202300XXX
A novel and efficient approach has been established for the synthesis of demanding L-glycosyl fluorides. This approach is exemplified by the convenient preparation of L-glucosyl and L-galactosyl fluorides from readily available β-D-C-glucosyl and β-D-C-mannosyl derivatives. The transformation features the equipment of hydroxymethyl group at the anomeric position under mild conditions and the head-to-tail inversion of sugar rings through radical decarboxylative fluorination of uronic acids. The effectiveness of this protocol is demonstrated by the first assembly of a pentasaccharide repeating unit of extracellular polysaccharide S-88. This was made possible by the facile equipment of L-mannosyl unit with L-mannosyl fluoride as glycosylating agent and the efficient extension of sugar chain at the sterically hindered hydroxy group. Our work not only enriches the methodologies for preparing L-sugar building blocks, but also holds promise for the synthesis of glycans containing L-sugar residues.