Reaction Steps
As described for the synthesis of 3′,5′-bis-O-(tert-butyldimethylsilyl)-O6-(4-nitrophenyl)-2′-deoxyinosine, this fluorenyl 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), Cs2CO3 (65.2 mg, 0.200 mmol) and 2-hydroxyfluorene (20.0 mg, 0.110 mmol) in dry DME (1.0 mL) at 85° C. for 1 h. Chromatographic purification (SiO2, elution with 20% EtOAc in hexanes) afforded 56.0 mg (87% yield) of the title compound as a clear, yellowish gum. Rf (20% EtOAc in hexanes)=0.31. 1H NMR (500 MHz, CDCl1): δ 8.52 (s, 1H, Ar—H), 8.41 (s, 1H, Ar—H), 7.83 (d, 1H, Ar—H, J=8.3), 7.77 (d, 1H, Ar—H, J=7.3), 7.53 (d, 1H, Ar—H, J=7.3), 7.45 (s, 1H, Ar—H), 7.37 (t, 1H, Ar—H, J=7.6), 7.29 (t, 1H, Ar—H, J=7.8), 6.55 (t, 1H, H-1′, J=6.4), 4.66 (m, 1H, H-3′), 4.05 (q, 1H, H-4′, J=3.4), 3.94 (s, 2H, CH2), 3.92 (dd, 1H, H-2′, J=11.2, 4.1), 3.81 (dd, 1H, H-2′, J=11.2, 2.9), 2.67 (app quint, 1H, H-2′, Japp˜6.3), 2.50 (ddd, 1H, H-2′, J=13.2, 6.0, 4.3), 0.94, 0.93 (2 s, 18H, tert-Bu), 0.12 (s, 12H, SiCH3). 13C NMR (126 MHz, CDCl1): δ 160.5, 152.5, 152.1, 151.6, 144.7, 143.3, 141.6, 141.1, 139.5, 126.8, 126.5, 124.9, 122.2, 120.5, 120.47, 119.7, 118.7, 88.1, 84.7, 71.9, 62.8, 41.5, 37.0, 25.9, 25.7, 18.4, 18.0, −4.7, −4.8, −5.4, −5.5. FAB HRMS calcd for C35H49N4O4Si2 (M++H) 645.3292. found 645.3303.
