Treatment of 205 with dilute acid liberated 5-deoxy-D-ribose which was immediately acetylated in the presence of acetic anhydride, giving an anomeric mixture of 5-deoxy-1,2,3-tri-O-acetyl-β-D-ribofuranose (206). The 5-deoxy-1,2,3-tri-O-acetyl sugar was used as an anomeric mixture for ribosylation of 2,5,6-trichlorobenzimidazole in a manner similar to its 1,2,3,5-tetra-O-acetyl-β-D-ribofuranose counterpart. Thus, silylation of the chlorinated heterocycle (207) was followed by the addition of TMSOTf and 5-deoxy-1,2,3-tri-O-acetyl-β-D-ribofuranose (206) to afford a mixture of the α and β anomers of 2,5,6-trichloro-1-(5'-deoxy-2,3-di-O-acetyl-D-ribofuranosyl)benzimidazole. Separation of these anomers was achieved by chromatography, and deprotection of the β anomer gave the 5'-deoxy TCRB (210).
