InChI=1S/C20H18O6/c1-2-3-4-5-6-11-14(22)9-13-17(19(11)25)20(26)16-12(18(13)24)7-10(21)8-15(16)23/h5-9,21-23,25H,2-4H2,1H3/b6-5+