Synthesis of Naturally Occurring C-Nucleosides, Their Analogs, and Functionalized C-Glycosyl Precursors

Abstract

Publisher Summary The C-nucleosides are a group of C-glycosylated heterocycles in which the anomeric carbon atom is attached to the heterocycle by a C-C bond. C-nucleosides have been mainly from fermentation sources, and have been found to exhibit a variety of interesting biological properties. Pyrazomycin has significant antiviral activity. Formycin, formycin B, and oxazinomycins exhibit, in addition, antitumor activity. The biological importance of most of the naturally occurring C-nucleosides has prompted the exploration of synthetic routes leading to these compounds and their analogs. As synthetic targets, the C-nucleosides have deceptively simple structures, and the design of synthetic routes to them must take two important factors into account. Firstly, the methods selected for C-C bond formation at the anomeric center should be stereocontrolled because the structures known thus far are, with two exceptions, β-D-glycosyl compounds. Secondly, the carbon atom attached to the glycosyl group in a C-nucleoside precursor should be appropriately substituted or be amenable to substitution, so as to allow the elaboration of the other heterocyclic portion of the molecule.