InChI=1S/C21H20O9S/c1-27-20-9-13(4-7-17(20)23)3-6-16-11-15(22)12-19(29-16)14-5-8-18(21(10-14)28-2)30-31(24,25)26/h3-11,19,23H,12H2,1-2H3,(H,24,25,26)/b6-3+