To a mixture of 41 (0.1 g, 0.218 mmol) and BOP [Castro's Reagent, Benzotriazole-1-yl-oxy-tris-(dimethylamino)-phosphonium hexafluorophosphate] (0.144 g, 0.326 mmol) in 5 mL dichloromethane was added triethylamine (0.067 mL, 0.477 mmol). The mixture was stirred for 1 h, and then sodium methoxide (0.5 M solution in methanol, 0.07 mL, 0.035 mmol) was added with 5 mL MeOH. The reaction was allowed to stir at room temperature for 16 h. 5% HCl was added to pH 0 and the mixture was extracted with 25 mL dichloromethane three times. The combined organic layers were washed with brine, dried over MgSO4, filtered and concentrated. The residue was loaded onto silica gel column as a solution in dichloromethane. The product was eluted with hexanes-ethyl acetate (3:2). Fractions were concentrated in vacuum to a white solid (0.037 g, 36.4%). 1H NMR (400 MHz, DMSO-d6) δ 12.05 (br s, 1H), 7.75 (s, 1H), 7.30 (d, J=8.8 Hz, 2H), 7.18 (d, J=8.8 Hz, 2H), 7.06 (d, J=8.0 Hz, 2H), 7.02 (d, J=8.8 Hz, 2H), 6.99 (d, J=8.8 Hz, 2H), 6.98 (d, J=8.0 Hz, 2H), 4.91 (dd, J=4.8 and 9.6 Hz, 1H), 3.72 (s, 3H), 3.39 (dd, J=4.0 and 13.6 Hz, 1H), 3.13 (dd, J=9.2 and 14.0 Hz, 1H), 2.25 (s, 3H).
