InChI=1S/C21H20O8/c22-12-20(28)21(29,18(26)9-4-13-1-6-15(23)7-2-13)19(27)10-5-14-3-8-16(24)17(25)11-14/h1-11,20,22-25,28-29H,12H2/b9-4+,10-5+