InChI=1S/C21H20O9/c22-13-5-1-11(9-17(13)26)3-7-15(24)19(28)21(30)20(29)16(25)8-4-12-2-6-14(23)18(27)10-12/h1-10,19-23,26-30H/b7-3+,8-4+