Sialic acid donors: Chemical synthesis and glycosylation

Sialic acids (or ulosonic acids) are a family of acidic ketoses (including neuraminic acid, KDN and KDO) that are found at the non-reducing terminus of many glycoconjugates. These saccharide residues are recognized ligands of protein lectins and are removed in the first step in glycoconjugate catabolism. Moreover, sialic acid containing carbohydrates, such as glycolipid gangliosides (i.e. GM3), glycopeptides (i.e. Tn) and polysaccharides (i.e. polysialic acid or colominic acid) play important biological roles. Thus, they represent important targets in natural product synthesis. This review examines the application of sialic acids as donors in glycosylation reactions. The synthesis of protected sialic acid donors and challenges associated with their use in the synthesis of heteronuclear and carbon glycosides are discussed.