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with saturated aq. NaHCO3, and distributed between dichloromethane and
water. The combined organic extracts were dried and concentrated to an oil
that was purified by flash chromatography eluting with dichloromethane:
methanol (19:1). Product fractions were combined and concentrated to
give 20 (130 mg, 43% yield): 1H NMR (400 MHz, CDCl3 + D2O): δ 8.72 (s,
1H), 8.13 (s, 1H), 6.07 (s, 1H), 5.48–5.41 (m, 1H), 4.99 (s, 1H), 4.35 (s,
1H), 3.77 (d, J = 5.3 Hz, 2H), 3.34–3.21 (m, 2H), 2.92–2.60 (m, 4H), 1.61
(s, 3H), 1.56 (s, 9H), 1.42 (s, 9H), 1.39 (s, 3H).
tert-Butyl (9-((3aR,4R,6R,6aR)-6-(12,12-dimethyl-7,10-dioxo-11-oxa-2,6,-
9-triazatridecyl)-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl)-9H -pur-
in-6-yl)carbamate (21). Reaction of 19 (127 mg, 0.55 mmol) with 8 followed
by purification, as described for the synthesis of 20, gave 21 (153 mg, 48%
1
yield): H NMR (400 MHz, CDCl3): δ 8.70 (s, 1H), 8.10 (s, 1H), 7.15 (d, J
= 6.5 Hz, 1H), 6.09 (d, J = 2.5 Hz, 1H), 5.47–5.36 (m, 2H), 5.07 (dd, J =
6.4, 3.4 Hz, 1H), 4.50–4.47 (m, 1H), 3.68 (d, J = 5.8 Hz, 2H), 3.30 (d, J =
6.2 Hz, 2H), 3.20–3.08 (m, 2H), 2.81–2.71 (m, 2H), 1.80–1.70 (m, 2H), 1.60
(s, 3H), 1.55 (s, 9H), 1.42 (s, 9H), 1.37 (s, 3H).
2-Amino-N-(2-((((2R,3S,4R,5R)-5-(6-amino-9H-purin-9-yl) -3,4-dihydrox-
ytetrahydrofuran-2-yl)methyl)amino)ethyl)acetamide (4). To a solution of 20
(130 mg, 0.21 mmol) in dichloromethane (0.8 mL) at 0◦C was added water
(0.2 mL) and TFA (1.1 mL). The mixture was stirred at room temperature
overnight and concentrated to a residue that was dissolved in methanol:
water (5:95) and purified by preparative reverse-phase HPLC (Restek Ultra
C18, 5 μm, 150 × 21.2 mm column; flow rate of 10 mL/min using an isocratic
elution of 2% acetonitrile in water for 10 min) followed by concentration and
lyophilization of fractions yielding 4 (44 mg, 56% yield): 1H NMR (400 MHz,
DMSO-d6 + D2O): δ 8.47 (s, 1H), 8.31 (s, 1H), 5.97 (d, J = 5.4 Hz, 1H),
4.65 (t, J = 5.0 Hz, 1H), 4.23–4.19 (m, 2H), 3.51 (s, 2H), 3.46–3.30 (m, 4H),
3.08–2.99 (m, 2H); MS (ESI): m/z 367.1841 (M+1)+.
2-Amino-N-(3-((((2R,3S,4R,5R)-5-(6-amino-9H-purin-9-yl) -3,4-dihydrox-
ytetrahydrofuran-2-yl)methyl)amino)propyl)acetamide (5). To a solution of
21 (185 mg, 0.3 mmol) in dichloromethane (1.2 mL) at 0◦C was added water
(0.3 mL) and TFA (1.5 mL). The mixture was stirred at room temperature
overnight and concentrated to a residue that was dissolved in methanol:
water (5:95) and purified by preparative reverse-phase HPLC (Restek Ultra
C18, 5 μm, 150 × 21.2 mm column; flow rate of 10 mL/min using an isocratic
elution of 2% acetonitrile in water for 10 min) followed by concentration and
lyophilization of fractions yielding 5 (62 mg, 54% yield): 1H NMR (400 MHz,
DMSO-d6 + D2O): δ 8.42 (s, 1H), 8.31 (s, 1H), 5.95 (d, J = 5.3 Hz, 1H),
4.63 (t, J = 5.0 Hz, 1H), 4.25–4.15 (m, 2H), 3.50 (s, 2H), 3.36 (dd, J =
13.2, 9.6 Hz, 1H), 3.24 (dd, J = 13.4, 2.8 Hz, 1H), 3.12 (t, J = 6.8 Hz,
2H), 2.90 (t, J = 7.7 Hz, 2H), 1.79–1.64 (m, 2H); MS (ESI): m/z 381.2000
(M+1)+.