11,14-Dioxa-2,9-diazaheptadec-16-enoic acid,10,15-dioxo-12-[[(1-oxo-2-propenyl)oxy]methyl]-,2-[(1-oxo-2-propenyl)oxy]-1-[[(1-oxo-2-propenyl)oxy]methyl]ethyl ester