Ribosylation of the base residue of inosine derivatives by phase-transfer catalysis

Reaction of 2',3',5'-O -silylated inosine derivative 1 with 2,3-O-isopropylidene-5-O-tritylribosyl chloride (3) in a two-phase (CH2Cl2-aq. NaOH) system in the presence of Bu(4)NBr gave three products, i.e., 6-O-alpha-, 6-O-beta-, and N-1-beta-isomers of glycoside a 4, 5a, and 5b. A similar PTC reaction of 1 with 2,3,5-tri-O-benzylribosyl bromide (9) gave four regio- and stereo-isomers involving the N-1-beta-glycoside 10. Reaction of 1 with 2,3,5-tri-O benzoylribosyl bromide (11) afforded three products involving the desired N-1-beta-glycoside 12b, which could be deprotected to give N-1-ribosylinosine (15b) as a useful intermediate for the synthesis of cIDPR.