Methyl morpholine oxide → 2'-O-(2-Hydroxyethyl)-3',5'-bis(tert-butyldiphenylsilyl)guanosine

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Reaction Steps

Compound 124 (9 g, 11.23 mmol) was dissolved in CH2Cl2 (80 mL). To the clear solution acetone (50 mL), 4-methyl morpholine-N-oxide (1.89 g, 16.17 mmol) was added. The reaction flask was protected from light. Thus 4% aqueous solution of osmium tetroxide was added and the reaction mixture was stirred at room temperature for 6 hr. Reaction volume was concentrated to half and ethyl acetate (50 mL) was added. It was then washed with water (30 mL) and brine (30 mL). Ethyl acetate layer was dried over anhydrous Na2SO4 and evaporated to dryness. Residue was then dissolved in CH2Cl2 and NaIO4 adsorbed on silica (21.17 g, 2 g/mmol) was added and stirred with the reaction mixture for 30 min. The reaction mixture was filtered and silica was washed thoroughly with CH2Cl2. Combined CH2Cl2 layer was evaporated to dryness. Residue was then dissolved in dissolved in 1M pyridinium-p-toluene sulfonate (PPTS) in dry MeOH (99.5 mL) under inert atmosphere. To the clear solution sodium cyanoborohydride (1.14 g, 18.2 mmol) was added and stirred at room temperature for 4 hr. 5% aqueous sodium bicarbonate (50 mL) was added to the reaction mixture slowly and extracted with ethyl acetate (2×50 mL). Ethyl acetate layer was dried over anhydrous Na2SO4 and evaporated to dryness. Residue placed on a flash column and eluted with 10% MeOH in CH2Cl2 to yield 125 (6.46 g, 72% yield). MS (Electrospray−) m/e 802 (M−H⊕)

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