InChI=1S/C20H18O6/c1-11-2-5-13-18(26-10-11)9-17(24)19(20(13)25)15(22)7-4-12-3-6-14(21)16(23)8-12/h2-4,6-9,21,23-25H,5,10H2,1H3/b7-4+