4.1.16  Methyl 4-({[(4R,6R)-6-(6-amino-9H-purin-9-yl)-2,2-dimethyl-tetrahydro-2H-furo[3,4-d] [1,3]dioxol-4-yl]methyl}(2-{[(2R,5R)-2-(6-amino-9H-purin-9-yl)-4-[(tert-butyldimethylsilyl)oxy]-5-{[(tert-butyldimethylsilyl)oxy]methyl}oxolan-3-yl]oxy}ethyl)amino)butanoate (25)
Following method D with 20 (600 mg, 0.73 mmol, 1.00 eq) and methyl-4-bromobutyrate, 25 (390 mg, 58%) was obtained as a white solid. Rf 0.34 (MeOH/DCM 5:95). 1H NMR (600 MHz, CDCl3) δ 8.32 (s, 1H), 8.31 (s, 1H), 8.17 (s, 1H), 7.90 (s, 1H), 6.11 (d, J = 3.6 Hz, 1H), 6.02 (m, 5H), 5.45 (dd, J = 6.5 Hz, J = 2.2 Hz, 1H), 4.91 (dd, J = 6.6 Hz, J = 3.3 Hz, 1H), 4.51 (t, J = 5.3 Hz, 1H), 4.32–4.23 (m, 2H), 4.08 (dt, J = 6.1 Hz, J = 3.2 Hz, 1H), 3.99 (dd, J = 11.5 Hz, J = 3.6 Hz, 1H), 3.76 (dd, J = 11.5 Hz, J = 2.8 Hz, 1H), 3.71–3.60 (m, 5H), 2.77 (dd, J = 13.5 Hz, J = 6.9 Hz, 1H), 2.74–2.69 (m, 2H), 2.64 (dd, J = 13.5 Hz, J = 6.8 Hz, 1H), 2.51–2.44 (m, 2H), 2.32–2.18 (m, 2H), 1.69–1.61 (m, 2H), 1.58 (s, 3H), 1.37 (s, 3H), 0.92 (s, 9H), 0.90 (s, 9H), 0.13–0.04 (m, 12H). 13C NMR (150 MHz, CDCl3) δ 174.0, 155.7, 155.6, 153.2, 153.1, 149.7, 149.4, 140.1, 139.5, 120.5, 120.3, 114.4, 91.1, 87.2, 85.7, 84.8, 83.9, 83.3, 82.5, 69.8, 69.3, 61.9, 56.7, 54.3, 53.7, 51.6, 31.5, 27.2, 26.1, 25.8, 25.5, 22.6, 18.6, 18.2, −4.4, −4.6, −5.2, −5.2. HRMS (ESI+): m/z calcd for C42H70N11O9Si2 [M+H]+: 928.4897, found: 928.4900.