Reaction Steps
As described for the synthesis of 3′,5′-bis-O-(tert-butyldimethylsilyl)-O6-methyl-2′-deoxyinosine, the isopropyl derivative was prepared by a reaction between O6-(benzotriazol-1-yl)-3′,5′-bis-O-(tert-butyldimethylsilyl)-2′-deoxyinosine (26) (59.8 mg, 0.100 mmol) and 2-propanol (1 mL) in the presence of Cs2CO3 (65.2 mg, 0.200 mmol) over 10 h. Chromatographic purification (SiO2, elution with 20% EtOAc in hexanes) afforded 44.1 mg (84% yield) of the title compound as a clear gum. Rf (20% EtOAc in hexanes)=0.31. 1H NMR (500 MHz, CDCl3): δ 8.50 (s, 1H, Ar—H), 8.23 (s, 1H, Ar—H), 6.49 (t, 1H, H-1′, J=6.3), 5.67 (septet, 1H, —CH—, J=6.3), 4.61 (m, 1H, H-3′), 4.02 (m, 1H, H-4′), 3.87 (dd, 1H, H-5′, J=11.2, 3.9), 3.78 (dd, 1H, H-5′, J=10.7, 2.9), 2.63 (app quint, 1H, H-2′, Japp˜6.3), 2.44 (ddd, 1H, H-2′, J=13.2, 5.9, 3.9), 1.47 (d, 6H, CH3, J=6.5), 0.91 (s, 18H, tert-Bu), 0.10, 0.09 (2 s, 12H, SiCH3). 13C NMR (126 MHz, CDCl3): δ 160.5, 152.0, 151.5, 140.3, 122.0, 87.9, 84.4, 71.9, 71.2, 62.8, 41.4, 26.0, 25.7, 22.0, 18.4, 18.0, −4.7, −4.8, −5.4, −5.5. FAB HRMS calcd for C25H47N4O4Si2 (M++H) 523.3136. found 523.3130.
