1a,7a,18a-trimethyl-2,3,6a,7a,8,9,18,18a,21a,21b-decahydro-1aH,6H,20H-spiro[18,20-methanooxireno[h]oxireno[8,9][1,6,12]trioxacyclooctadecino[3,4-d]chromene-19,2'-oxirane]-6,11,16-trione