Synthesis of 2,3-dihydroinosine derivatives by reduction using BH3-THF.

A novel reductive method for the chemical modification of nucleosides is described. Reaction of inosine derivatives with boran-THF resulted in the regioselective reduction of purine ring to afford the corresponding 2,3-dihydroinosine derivatives in moderate yields.

Substitution effect of purine nucleosides on diisobutylaluminum hybride reduction.

It is reported that the diisobutylaluminum hydride (DIBALH) reduction of inosine and adenosine derivatives (1a and 1d) causes cleavage of the ribose moiety to give the corresponding 9-ribitylhypoxanthine (2a) and 9-ribityladenine (2d), respectively. The substitution effect of purine nucleosides on the reduction was investigated. O6-alkylinosine derivatives (1b and 1c) were reduced in good yields like 1a. Introduction of methyl group into the N6-position of adenosine (1d), however, greatly reduced the reactivity toward DIBALH. The reduction of 7-deazainosine (3a) and 7-deazaadenosine (3b) hardly proceeded. These results suggest that oxygenophilicity of aluminum atom facilitates coordination of DIBALH to the 7-ring nitrogen atom and accelerate a cleavage of the ribose.