4,13-dimethyl-4a,5,8,9,19,20-hexahydro-2H,13H,18H-4,5:12,13-dimethanodipyrano[3,4-g:4',3'-n][1,4,9,13]tetraoxacycloheptadecine-2,6,11,15(4H,12H,12aH)-tetrone