Reaction Steps
A 1 L pear shaped recovery flask with stir bar was charged with a mixture of 16 (50 g, 134 mmol), silver acetylacetonate (41 g 200 mmol), TMSH (200 ml of 1N solution in methanol) and dimethylformamide (400 ml). The flask was heated to 70° C. for two hours. The solution was cooled to ambient temperature, neutralized to pH 7 with 1M HCl, and dried to a solid tar. The tar was dissolved in water (500 ml) and filtered through a sintered glass funnel to remove silver salts. The product was evaporated to dryness to remove water and residual solvents and 10 grams (26 mmols) was redissolved in 50 ml of water prior to purification on a Waters Delta-Pak ODS 50 mm×300 mm HPLC column. The N1-Bz-2′-OMe guanosine isomer eluted first and was recovered using a rotary evaporator. The product (7 g, 18 mm, 70%) was identical to an authentic sample by HPLC, UV-, 1H-NMR-spectroscopy. 1H NMR (dmso-d6): 8.02 (s, 1H, H8), 7.26 (m, 5H, ph), 7.02 (bs, 2H, 2NH2), 5.82 (d, J1′,2′=6.4, 1H, H1′), 5.23 (s, 2H, CH2-Bz), 5.18 (d, JOH,3′=4.8, 1H, 3′-OH), 5.04 (t, JOH,5′=5.2, JOH,5″=5.6, 1H, 5′-OH), 4.28 (m, J3′,2′=4.8, J3′,4′=3.2, 1H, H3′), 4.20 (t, J2′,1′=6.4, J2′,3′=4.8, 1H, H2′), 3.90 (m, J4′,3′=3.6, J4′,5′=4.0, 1H, H4′), 3.65-3.53 (m, 2H, H5′, H5″ JOH,5′=5.2, J5′,5″=11.6), 3.33 (s, 3H, OCH3).
