(αR,α'R)-1',2',3',4'β,9,9',10,10'-Octahydro-1,3'α,8,8',9'β-pentahydroxy-4'aβ,9'aβ-oxy-1',9,10,10'-tetraoxo-α,α',3,3'-tetramethyl-7,7'-bi(4-anthracenemethanol)α,α'-diacetate