(3S,4aS,7S,7aR)-3-hydroxy-4,4,7,7a-tetramethyl-11-[(1S,3E)-1-methyl-2-oxopent-3-en-1-yl]-1,2,3,4,4a,5,6,7,7a,8-decahydrobenzo[d]xanthene-9,12-dione