InChI=1S/C21H20O8/c1-9(8-22)4-5-12-11(3)18-15(7-13(12)23)28-19-16(21(27)29-18)10(2)6-14(24)17(19)20(25)26/h4,6-7,22-24H,5,8H2,1-3H3,(H,25,26)/b9-4+