Reaction Steps
In a clean, dry reaction vial equipped with a stirring bar were placed O6-(benzotriazol-1-yl)-3′,5′-bis-O-(tert-butyldimethylsilyl)-2′-deoxyinosine (26) (59.8 mg, 0.100 mmol), Cs2CO3 (65.2 mg, 0.200 mmol) and dry DME (1.0 mL). Morpholine (17.5 μL, 0.200 mmol) was added, the reaction mixture was flushed with N2, and the mixture was allowed to stir at room temperature for 1 h. The reaction mixture was concentrated and the residue was dissolved in EtOAc. The mixture was washed with 10% aq citric acid, sat aq NaHCO3 and brine. The organic layer was dried over Na2SO4 and evaporated to dryness. No additional purification was needed and 43 mg (78% yield) of the title compound was obtained. Rf (3% MeOH in CH2Cl2)=0.18. 1H NMR (500 MHz, CDCl3): δ 8.34 (s, 1H, Ar—H), 8.02 (s, 1H, Ar—H), 6.46 (t, 1H, H-1′, J=6.6), 4.59 (m, 1H, H-3′), 4.30 (br s, 4H, 2CH2), 4.01 (app q, 1H, H-4′, Japp˜3.4), 3.85-3.82 (m, 5H, H-5′ and 2CH2), 3.76 (dd, 1H, H-5′, J=11.0, 3.2), 2.59 (app quint, 1H, H-2′, Japp˜6.5), 2.42 (ddd, 1H, H-2′, J=13.2, 5.9, 3.9), 0.91 (s, 18H, tert-Bu), 0.09, 0.08, 0.076 (3 s, 12H, SiCH3). 13C NMR (126 MHz, CDCl3): δ 153.9, 152.3, 150.6, 136.8, 120.4, 87.8, 84.1, 72.0, 67.0, 62.8, 45.6, 41.1, 26.0, 25.7, 18.4, 18.0, −4.7, −4.8, −5.4, −5.5. FAB HRMS calcd for C26H48N5O4Si2 (M++H) 550.3245. found 550.3222.
