An efficient method for the synthesis of beta-D-ribonucleosides catalyzed by metal iodides

Several beta-D-ribonucleosides were synthesized in high yields under mild conditions by N-glycosylations of methyl 2,3,5-tri-O-benzoyl-beta-D-ribofuranosyl carbonate (1) with trimethylsilylated nucleoside bases in acetonitrile using a catalytic amount of metal iodide such as SnI2, SbI3 or TeI4. A deprotection of N-6-benzoyl group of coupling product took place to a considerable extent when N-6-benzoyl-N-6,N-9-bis(trimethylsilyl)adenine was employed as a nucleoside base using SnI2 or SnCl2 as a catalyst while it was minimized when SbI3 or TeI4 was used. Further, the N-glycosylation of 1 with 7-trimethylsilyltheophylline in the presence of a catalytic amount of metal iodide was more effectively achieved in nitrile solvents other than acetonitrile.