InChI=1S/C20H18O6/c1-11(9-21)2-7-14-16(23)8-17(24)18-19(25)15(10-26-20(14)18)12-3-5-13(22)6-4-12/h2-6,8,10,21-24H,7,9H2,1H3/b11-2+