[Cl:1][C:2]1[N:10]=[C:9]2[C:5]([N:6]=[CH:7][N:8]2[C@@H:11]2[CH2:15][C@H:14]([OH:16])[CH:13]=[CH:12]2)=[C:4]([Cl:17])[N:3]=1.N1C=CC=CC=1.Cl[C:25]([O:27][CH2:28][CH3:29])=[O:26]>C1COCC1>[CH2:28]([O:27][C:25](=[O:26])[O:16][C@H:14]1[CH2:15][C@@H:11]([N:8]2[CH:7]=[N:6][C:5]3[C:9]2=[N:10][C:2]([Cl:1])=[N:3][C:4]=3[Cl:17])[CH:12]=[CH:13]1)[CH3:29](1S,4R)-4-(2,6-Dichloro-purin-9-yl)-cyclopent-2-enol (9.5 g, 35.05 mmol) is placed in an oven-dried flask under an atmosphere of argon. Dry THF (200 mL) is added followed by dry pyridine (5.54 g, 70.1 mmol). Ethyl chloroformate (15.21 g, 140.2 mmol) is added slowly so that the temperature does not rise above 40-C and the reaction mixture is stirred at room temperature. The reaction is shown to be complete by LCMS after 1 hour. The solvent is removed in vacuo and the residue is partitioned between dichloromethane (200 mL) and water (200 mL). The organic layer is washed with water (150 ml) and brine (150 ml), dried over MgSO4, filtered and the solvent is removed in vacuo. The title compound is obtained after crystallisation from methanol. 1H nmr (CDCl3, 400 MHz); 8.20(s, 1H), 6.45(m, 1H), 6.25(m, 1H), 5.75(m, 1H), 5.70(m, 1H), 4.25(q, 2H), 3.20(m, 1H), 2.05(m, 1H), 1.35(t, 3H), MS (E+) m/e 343 (MH+).
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