1,2-<i>Trans</i>-Selective Synthesis of Glycosyl Boranophosphates and Their Utility as Building Blocks for the Synthesis of Phosphodiester-Linked Disaccharides

A highly 1,2-<i>trans</i>-selective synthesis of glycosyl boranophosphate derivatives by glycosylation of dimethyl boranophosphate with glycosyl iodides was developed. A study on the reaction mechanism indicated that the stereoselectivity of the reactions is controlled by neighboring group participation. The resultant glycosyl boranophosphate triesters were converted into the corresponding boranophosphate diesters and condensed with appropriately protected monosaccharides to give disaccharides linked with an anomeric boranophosphate linkage. Furthermore, the disaccharides worked as precursors of the corresponding phosphodiester-linked disaccharides. The whole synthesis of boranophosphate-linked disaccharides and their conversion to the phosphodiester-linked disaccharides were accomplished in good yields without loss of stereopurity at the anomeric position, indicating that the method is useful to synthesize diastereopure glycosyl phosphate-containing biomolecules.