A mixture of (2R,3R,4R,5R)-2-((benzoyloxy)methyl)-5-(4-chloro-5-iodo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)tetrahydrofuroyl-3,4-diyl dibenzoate (3.0 g, 4.1 mmol) was used as a raw material, and a mixture of it with aqueous ammonia solution (45 ml) and 1,4-dioxane (45 ml) was reacted at 80 °C The reaction was stirred for 16 hours. The completion of the reaction was confirmed by LC-MS analysis. The reaction mixture was concentrated to remove the solvent to give a residue. The residue was suspended in a solvent mixture of CH2Cl2/MeOH (9:1) and purified by passing through a column pre-filled with silica gel (using CH2Cl2/MeOH (9:1→1:1) as eluent). The eluate containing the target product was collected and concentrated to afford (2R,3R,4S,5R)-2-(4-amino-5-iodo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-5-(hydroxymethyl)tetrahydrofuran-3,4-diol (1.1 g, 69% yield) as a white solid. The product was characterized by 1H NMR (DMSO-d6): δ 8.10 (s, 1H), 7.68 (s, 1H), 6.68 (br s, 2H), 6.03 (d, 1H), 5.33 (br s, 1H), 5.15 (br, 2H), 4.36 (br s, 1H), 4.07 (br s, 1H), 3.88 (m, 1H). 3.56 (m, 2H).