2 N solution of HCl in ether (15 ml) was added in stirring solution of compound 5 (10.0 g, 21.9 mmol) in methanol at 0° C. The mixture was allowed to warm to room temperature gradually and continue stirred for 2 hr. Solvent was evaporated under reduced pressure, and the residue was treated with anhydrous ether (120 mL) to precipitate the product 6. The precipitated product was washed with ether (50 mL×2) afforded the titled compound as white solid. [α]D25 −28.19°; 1H NMR (500 MHz, DMSO-d6): δ 8.40 (bs, 2H, D2O exchange, NH2), 7.88 (m, 4H), 7.64 (m, 2H), 7.45 (m, 4H), 5.48 (m, 2H), 5.07 (m, 1H), 3.96 (m, 1H), 3.61 (m, 1H), 3.52 (m, 1H), 2.47 and 2.39 (m, 1H), 1.63 (m, 1H); HR-MS Calcd. For (C20H21NO5)+ 355.1420, found 335.1293.
