To a solution of compound 19C (18 mg, 0.023 mmol) in 1,2-dichloroethane (0.5 ml), was added acetic acid (13 μL, 0.23 mmol) and sodium triacetoxyborohydride (9.7 mg, 0.046 mmol) at room temperature. After being stirred for 3 hours, the mixture was treated with EtOAc (10 mL) and water (3 mL). The organic layer was washed with brine (2 mL), dried (MgSO4), filtered, and concentrated under reduced pressure to furnish the crude product. This material was purified on reverse phase HPLC eluting with acetonitrile and water (with 0.1% TFA) to afford the title product. 1H NMR (400 MHz, CD3OD) δ 8.71 (d, J=8.5 Hz, 1H), 8.09 (s, 1H), 7.41 (dd, J=7.0, 2.3 Hz, 1H), 7.33 (m, 1H), 7.20 (dd, J=10.8, 8.5 Hz, 1H), 6.97-6.61 (m, 3H), 6.42 (d, J=6.2 Hz, 2H), 5.24 (t, J=7.2 Hz, 1H), 5.13-4.96 (m, 2H), 4.51 (m, 2H), 4.01-3.83 (m, 1H), 3.42 (m, 2H), 3.14-2.82 (m, 2H), 2.50 (m, 4H), 2.08-1.84 (m, 2H), 1.68-1.37 (m, 2H); MS (m/z) 756.22 [M+H]+.
