Reaction Steps
In a 50 mL round-bottomed flask equipped with a stirring bar were placed 3′,5′-bis-O-(tert-butyldimethylsilyl)-2′-deoxyinosine (22) (1.005 g, 2.090 mmol) and BOP (1.850 g, 4.181 mmol). THF (20 mL) and DIPEA (0.55 mL, 3.135 mmol) were added and the mixture was allowed stir at room temperature for 23 h. The mixture was evaporated and CH2Cl2 (50 mL) added. The mixture was washed with water, dried over Na2SO4 and concentrated. Chromatographic purification (SiO2, elution with 20% EtOAc in hexanes) afforded 1.038 g (83% yield) of compound 26 as a white foam. Rf (20% EtOAc in hexanes)=0.14. 1H NMR (500 MHz, CDCl3): δ 8.54 (s, 1H, Ar—H), 8.41 (s, 1H, Ar—H), 8.14 (d, 1H, Ar—H, J=8.3), 7.55-7.41 (m, 3H, Ar—H), 6.55 (t, 1H, H-1′, J=6.1), 4.65 (m, 1H, H-3′), 4.06 (q, 1H, H-4′, J=3.1), 3.92 (dd, 1H, H-5′, J=11.2, 3.9), 3.80 (dd, 1H, H-5′, J=11.2, 2.7), 2.65 (app quint, 1H, H-2′, Japp˜6.3), 2.52 (m, 1H, H-2′), 0.93, 0.92 (2 s, 18H, tert-Bu), 0.11 (s, 12H, SiCH3). 13C NMR (126 MHz, CDCl3): δ 159.0, 153.6, 151.3, 143.5, 128.9, 128.7, 124.8, 120.6, 120.0, 108.6, 88.2, 85.0, 71.6, 62.6, 41.7, 25.9, 25.7, 18.4, 18.0, −4.7, −4.8, −5.4, −5.5. FAB HRMS calcd for C28H44N7O4Si2 (M++H) 598.2993. found 598.2986.
