InChI=1S/C21H20O8/c22-15(13-4-2-1-3-5-13)11-8-12-6-9-14(10-7-12)28-21-18(25)16(23)17(24)19(29-21)20(26)27/h1-11,16-19,21,23-25H,(H,26,27)/b11-8+