9-(2,3,5-Tri-O-acetyl-β-D-ribofuranosyl)-6-hydroxymethyl-1,6-dihydropurine (VI) (217 mg.) obtained in (2) was dissolved in purified anhydrous dimethoxyethane (10 ml.) and cooled to -10° to -15° C. To the cooled solution were added sodium hydride (76 mg., 3 moles) and mesyl chloride (180 mg., 3 moles), successively. The reaction was conducted at 0° - 5° C. for 17 hours. The reaction mixture was then treated with water-chloroform and the chloroform layer thus separated was washed with 0.5% aqueous sodium hydrogen carbonate, then with water, dried over anhydrous sodium sulfate and concentrated to yield II as a pale-yellow oil (235 mg., yield: 91%). This substance is unstable and decomposes in chloroform within 2-3 hours.
