9-12 5'-Bis-o.uert-butyldimethylsilyl)-1-/H vylofuranosylladenine(5). To a mixture of NaBHoAcnyTHF/AcoH[generated in situ by adding Acoll(9 mLIto a suspension of NaBH. d g. 28.28(66 ml and stirred for 1.5 h at o c under Ar atmosphere) mmolo in THF was added compound 4 do g. 203 minolo. The reaction mixture was stirred for 4 h at o c. and then evaporated lo dryness. The residue was partitioned with EuoAchsat. NaHCo, and the aqueous layer was extracted with EoAc The combined organic layer was washed with Hro. brine. and dried over Na,son The mixture was then filtered, and evaporated to dryness. The oily residue was subjected to flash column chromatography to give compound 5 o 89 g. 89 oas a colorless powder