InChI=1S/C20H20O6/c1-11(9-21)2-4-14-17(23)7-6-15-19(25)16(10-26-20(14)15)13-5-3-12(22)8-18(13)24/h2-3,5-8,16,21-24H,4,9-10H2,1H3/b11-2+