Recent Progress in the Synthesis and Glycosylation of Rare Sugars

Out of 42 naturally occurring monosaccharides, only seven are abundant in Nature (glucose, galactose, mannose, fructose, xylose, ribose, and l -arabinose), while the others have been classified as 'rare sugars'. Fungi and bacteria use a wide range of monosaccharides, in contrast to mammals, reflected in their glycosylated metabolites, as well as the cellular machineries that are involved in their sugar metabolism. Recognition of the microbiome's impact on human health has led to increased interest in microbial glycans, as they often mediate interaction between host and microbes. Efficient access to rare sugars and oligosaccharides is necessary to study their roles in Nature, which can provide new pharmacological leads. Furthermore, it enables the synthesis of bioactive glycosylated natural products and congeners. This short review highlights recent progress in the synthesis and the efficient, site- and stereoselective glycosylation of rare sugars. Finally, it provides a recent example where synthetic access to rare sugars has enabled biochemical studies to better understand and interfere with processes in Nature.