Reaction Steps
To a stirred solution of the sodium salt (105 mg) obtained in Example 18 in 1.0 mL of DMF, was added pivaloyloxymethyl chloride (35.6 μl), and the mixture was stirred at room temperature for 16 hours. The reaction mixture was diluted with 20 mL of ethyl acetate, washed with water (4 times) and aqueous saturated sodium chloride solution, then dried over sodium sulfate, and concentrated. The residue was purified through silica gel column chromatography (0.7% methanol/chloroform) to obtain the 2-isomer and 1-isomer. 2-Isomer (major product): 1H-NMR (CDCl3) δ: 8.69 (1H, d, J=2.4 Hz), 8.32 (1H, dd, J=2.4, 8.8 Hz), 7.77 (1H, dd, J=1.0, 8.3 Hz), 7.47 (1H, dd, J=7.7, 8.3 Hz), 7.20 (1H, s), 7.16 (1H, d, J=8.8 Hz), 7.08 (1H, d, J=7.7 Hz), 6.50 (2H, s), 4.64-4.56 (1H, m), 4.24-4.17 (1H, m), 4.08 (3H, s), 4.03 (3H, s), 3.68-3.59 (1H, m), 3.40 (1H, td, J=12.9, 2.8 Hz), 2.88 (1H, d, J=16.6 Hz), 2.81 (1H, d, J=16.6 Hz), 2.28-2.20 (1H, m), 2.14-2.07 (1H, m), 2.01-1.88 (2H, m), 1.23 (9H, s). MS [M+H]+=615. 1-Isomer (minor product): 1H-NMR (CDCl3) δ: 8.30 (1H, d, J=2.4 Hz), 8.09 (1H, dd, J=8.8, 2.4 Hz), 7.78 (1H, dd, J=8.2, 1.0 Hz), 7.48 (1H, t, J=8.2 Hz), 7.25 (1H, d, J=8.2 Hz), 7.20 (1H, s), 7.08 (1H, d, J=8.8 Hz), 6.32 (1H, d, J=11.2 Hz), 6.29 (1H, d, J=11.2 Hz), 4.65-4.57 (1H, m), 4.28-4.20 (1H, m), 4.09 (3H, s), 4.04 (3H, s), 3.69-3.59 (1H, m), 3.40 (1H, td, J=12.8, 2.9 Hz), 2.90 (1H, d, J=16.6 Hz), 2.84 (1H, d, J=16.6 Hz), 2.28-2.21 (1H, m), 2.14-2.07 (1H, m), 2.06-1.89 (2H, m), 1.28 (9H, s). MS [M+H]+=615.
