C1C=CC(C(NC2C3NC=NC=3N=CN=2)=[O:8])=CC=1.C(N[C:23]1[CH:44]=[CH:43][N:26]([C@@H:27]2[O:42][C@H:36]([CH2:37][O:38]C(=O)C)[C@@H:31]([O:32]C(=O)C)[C@H:28]2[O:29]C)[C:25](=[O:45])[N:24]=1)(=O)C.[Si](OS(C(F)(F)F)(=O)=O)(C)(C)C>C(#N)C.ClCCl>[C@@H:27]1([N:26]2[CH:43]=[CH:44][C:23](=[O:8])[NH:24][C:25]2=[O:45])[O:42][C@H:36]([CH2:37][OH:38])[C@@H:31]([OH:32])[C@H:28]1[OH:29]
A solution of N6-benzoylaminopurine (Lancaster) (1.23 g, 5.16 mmol) stirring in anhydrous acetonitrile under an argon atmosphere was treated with BSA (3.82 ml, 15.48 mmol) at reflux for 3 hours. Upon cooling, a solution of N4-acetyl-5′,3′-di-O-acetyl-2′-O-methyl cytidine (2) (see above) (0.66 g, 1.72 mmol) in 20 ml anh. acetonitrile was added to the reaction mixture followed by TMStriflate (1.03 ml, 5.16 mmol). The reaction mixture was then heated to 75° C. for 16 hours while stirring under positive pressure argon. Upon cooling, an additional 1.03 ml (5.16 mmol) of TMStriflate was added, and the reaction heated to 75° C. for an additional 20 hours. Once cool, the reaction mixture was diluted with two volumes of dichloromethane and washed with sat. NaHCO3. The organic layer was then dried over Na2SO4 and evaporated in vacuo. Flash chromatography employing a gradient of 10 to 80% ethyl acetate/hexanes afforded (1) as a white foam; 0.403 g, 50% yield. 1H NMR (CDCl3): 8.88 (br s, 1H, NH), 8.81 (s, 1H, H8), 8.31 (s, 1H, H2), 8.11-7.53 (m, 5H, benzoyl), 6.18 (d, J1′,2′=4.8, 1H, H1′), 5.41 (t, J3′,2′=4.8, J3′,4′=4.8, 1H, H3′), 4.75 (t, J2′,1′=4.8, J2′,3′=4.8, 1H, H2′), 4.50-4.34 (m, 3H, H4′, H5′, H5″), 3.44 (s, 3H, OCH3), 2.19 (s, 3H, OAc), 2.14 (s, 3H, OAc).
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