Abstract
Disaccharide nucleosides are an important class of natural compounds that have a variety of biological activities. In this study, we report on the synthesis of disaccharide nucleosides utilizing the temporary protection of the 2′,3′-cis-diol of ribonucleosides, such as adenosine, guanosine, uridine, 5-metyluridine, 5-fluorouridine and cytidine, by a boronic ester. The temporary protection of the above ribonucleosides permits the regioselective O-glycosylation of the 5’-hydroxyl group with thioglycosides using a p-toluenesulfenyl chloride (p-TolSCl)/silver triflate (AgOTf) promoter system to afford the corresponding disaccharide nucleosides in fairly good chemical yields. The formation of a boronic ester prepared from uridine and 4-(trifluoromethyl)phenylboronic acid was examined by 1H, 11B and 19F NMR spectroscopy.
Highlights
Disaccharide nucleosides, which contain an external sugar moiety linked to one of the hydroxyl groups of the nucleoside via an O-glycoside bond, constitute an important class of natural compounds [1,2,3,4,5,6,7]
Several strategies for the synthesis of disaccharide nucleosides such as enzymatic O-glycosylation [20,21], chemical N-glycosylation [5,9,16,22,23,24] and chemical O-glycosylation [7,9,14,16,18,19,24,25,26,27,28,29,30,31,32,33,34,35,36,37] have been reported to date
Chemical O-glycosylation is often useful for the large-scale synthesis of the desired disaccharide nucleosides in higher chemical yields compared to chemical N-glycosylation
Summary
Disaccharide nucleosides, which contain an external sugar moiety linked to one of the hydroxyl groups of the nucleoside via an O-glycoside bond, constitute an important class of natural compounds [1,2,3,4,5,6,7]. It is reported that an excess amount of the glycosyl donor is required for glycosylation at the hydroxyl site to be complete, because it is likely that glycosylation preferentially proceeds on the nucleobase or other Lewis basic site [18,32,34,36]. Side reactions such as depurination (cleavage of the anomeric C–N bond of nucleosides), anomerization reaction and trans-purinylation have been reported [35,38,39]. The synthesis of disaccharide nucleosides via the O-glycosylation of ribonucleosides.
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