1a,9b-Dihydro-3,4,4,9-tetrahydroxy-7-methoxy-7-methylspiro[naphtho[2,3-b]furan-2(3H),2(5H)-oxireno[d]benzo[1,2-b:5,4-c]dipyran]-5,5,8-trione [ 11048-91-2 ]