Reaction Steps
A mixture of the protected flavonol (11) (600 mg, 1.49 mmol) in aqueous HCl (36%, 38 mL) and acetic acid (38 mL) was heated under reflux for 2 h. The mixture was then cooled on ice and diluted with water. The resulting suspension was centrifuged and the collected solid washed with water, then freeze-dried to afford the salt as a crude yellow solid (457 mg). A mixture of the crude yellow product and succinic anhydride (179 mg, 1.79 mmol) in pyridine was stirred at room temperature for 4 h. Water (1 mL) was added and the mixture was acidified with 2 M HCl. The mixture was left to stand at room temperature for 30 min, and the resulting suspension was centrifuged and the collected solid was washed with water, freeze-dried and recrystallised from DMF/water to afford the succinamic acid (2) as a brown powder (211 mg, 38.2%), m.p. 256-257° C. Anal. Calcd. for C19H16NO7.½H2O: C, 60.32; H, 4.26; N, 3.70. Found: C, 59.99; H, 4.53; N, 3.90. 1H NMR (399.7 MHz, d6-DMSO) δ 2.55-2.60 (m, 4H, CH2CH2); 6.93 (app. d, 2H, J=9.2 Hz, H3′,5′); 7.69 (d, 1H, J7,8 8.8 Hz, H8); 7.85 (dd, 1H, J5,7 2.8, J7,8 8.8 Hz, H7); 8.09 (app. d, 2H, J=9.2 Hz, H2′,6′); 8.43 (d, 1H, J5, 7 2.8 Hz, H5); 9.33 (s, 1H, NH); 10.11, 10.31 (2 br s, 2×1H, 2×OH); 12.21 (br s, 1H, CO2H). 13C NMR (100.5 MHz, d6-DMSO) δ 25.16, 28.78 (2C, CH2CH2); 31.06, 67.05, 112.65, 115.46, 118.80, 121.45, 122.06, 125.11, 129.55, 135.80, 137.57, 146.01, 150.38, 159.11 (14C, Ar); 170.40, 172.33, 173.86 (3C, 3×C═O).
