Reaction Steps
(see FIG. 8B) N2-Isobutyryl-2′-O-methylguanosine (6) (Inoue et al., Nucleic Acids Res. 1987, 15, 6131-6148, and is incorporated by reference herin in its entirety) (1.6 g, 4.36 mmol) was dissolved in dry pyridine (25 mL) and the solution was cooled to 0° C. while protected from moisture. p-Toluenesulfonyl chloride (1.0 g, 5.23 mmol) was added and the reaction mixture was left at 0-3° C. for 48 h. MeOH (10 mL) was added and the mixture evaporated to a syrup. After standard work up and column chromatography using 1-2% MeOH in CH2Cl2, 7 was obtained as a colorless foam, 1.06 g (47%), 1H NMR δ12.25 (br s, 1H, NH), 9.55 (br s, 1H, NH), 7.83 (d, JH,H=8.3, 2H, Ts), 7.78 (s, 1H, H8), 7.42 (d, JH,H=8.3, 2H, Ts), 5.83 (d, J1′,2′=6.2, 1H, H1′), 4.82 (app t, J2′,3′=5.7, 1H, H2′), 4.64 (m, 1H, H3′), 4.37 (dd, J5′,4′=2.2, J5′,5″=10.3, 1H, H5′), 5.23 (dd, J4′,5″=2.9, J4′,3′=5.2, 1H, H4′), 4.29 (dd, J5″,4′=2.9, J5″,5′=10.3, 1H, H5″), 3.47 (s, 3H), OMe), 2.76 (m, 1H, CH(CH3)2), 2.51 (s, 3H, Ts-Me),1.29 (m, 6H, 2×Me).
