Regio- and stereoselective glycosylation: Synthesis of 5-haloimidazole alpha-ribonucleosides

摘要

We describe the synthesis of novel 5-haloimidazole ribonucleosides as precursors of modified cobalamins. A regio and stereoselective glycosylation of protected ribose with silylated 4(5)-haloimidazoles produces 5-haloimidazole ribonucleosides predominantly in the alpha-configuration (60-75%) without any 4-substituted imidazole ribonucleoside. The structure of the 5-fluoroimidazole ribonucleoside was confirmed by X-ray crystallography and 2D NMR spectroscopy.