Reaction Steps
To a stirred solution of 9-(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)-2-amino-6-(2-propylimidazol-1-yl)purine (2.37 g, 4.72 mmol) in CH2Cl2 (120 mL) was added TMSCl (5.3 mL, 4.54 g, 42.5 mmol) dropwise under N2, and then BTEANO2 (7.1 g, 29.8 mmol) in CH2Cl2 (40 mL). Evolution of gas was observed, and when this subsided, additional TMSCl (5.3 mL) was added. The mixture was then stirred at ambient temperature for 3 h. The solution was diluted with CH2Cl2 and washed (NaHCO3/H2O, 2×200 mL+100 mL), and the aqueous layer was extracted with CH2Cl2. The combined organic phase was dried (Na2SO4), and volatiles were evaporated in vacuo. The residue was chromatographed (MeOH/CH2Cl2, 1:99-1:90) to give crude product (1.40 g, 57%, contaminated with Ph3PO), which was recrystallized (i-PrOH) to give 9-(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)-2-chloro-6-(2-propylimidazol-1-yl)purine: mp 126-127.5° C.; UV (MeOH) max 217, 287 nm (∈ 25 300, 15 000), min 238, 261 nm (∈ 4200, 6200); 1H NMR (500 MHz, CDCl3) δ 8.57 (d, J=1.8 Hz, 1H), 8.25 (s, 1H), 7.11 (d, J=1.5 Hz, 1H), 6.27 (d, J=5.5 Hz, 1H), 5.83 (t, J=5.5 Hz, 1H), 5.60-5.62 (m, 1H), 4.49-4.51 (m, 1H), 4.43-4.44 (m, 2H), 3.29 (t, J=7.7 Hz, 2H), 2.19 (s, 3H), 2.17 (s, 3H), 2.11 (s, 3H), 1.86 (sext, J=7.6 Hz, 2H), 1.07 (t, J=7.7 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 170.5, 169.9, 169.7, 154.6, 153.8, 151.6, 148.4, 142.5, 129.3, 123.0, 120.5, 86.6, 81.0, 73.5, 70.8, 63.2, 33.2, 21.6, 21.1, 20.8, 20.7, 14.2; HRMS m/z 520.1476 (M+[C22H25ClN6O7]=520.1473). Anal. Calcd For C22H25ClN6O7: C, 50.73; H, 4.84; N, 16.13. Found: C, 50.58; H, 4.87; N, 16.15.
