4.1.8  (2R,5R)-2-(6-amino-9H-purin-9-yl)-5-{[(2-{[(2R,5R)-2-(6-amino-9H-purin-9-yl)-4-hydroxy-5-(hydroxymethyl)oxolan-3-yl]oxy}ethyl)amino]methyl}oxolane-3,4-diol (1)
Following method C with 20 (117 mg, 0.14 mmol, 1.00 eq) and a 0–25% linear gradient of acetonitrile in TEAAc buffer 50 mM, pH 7 for purification, 1 (60 mg, 76%) was obtained as a white powder with 99% purity determined by HPLC analysis at 260 nm. 1H NMR (600 MHz, DMSO‑d 6) δ 8.38 (s, 1H), 8.34 (s, 1H), 8.15 (s, 1H), 8.14 (s, 1H), 7.36 (br.s, 2H), 7.29 (br. s, 2H), 5.97 (d, J = 6.4 Hz, 1H), 5.85 (d, J = 5.9 Hz, 1H), 5.58–4.98 (m, 4H), 4.70–4.63 (m, 1H), 4.52 (dd, J = 6.4 Hz, J = 4.7 Hz, 1H), 4.33 (dd, J = 4.7 Hz, J = 2.6 Hz, 1H), 4.12 (dd, J = 5.2 Hz, J = 3.8 Hz, 1H), 4.02–3.93 (m, 2H), 3.70–3.48 (m, 4H), 2.86–2.58 (m, 4H). 13C NMR (150 MHz, DMSO‑d 6) δ 156.2, 156.1, 152.6, 152.5, 149.4, 149.0, 140.1, 139.9, 119.4, 119.3, 87.6, 86.3 (2C), 83.7, 81.5, 72.8, 71.5, 69.5, 69.1, 61.7, 51.2, 49.0. HRMS (ESI+): m/z calcd for C22H30N11O7 [M+H]+: 560.23242, found: 560.23188.