4,7-Epoxy-2H-[1,6]dioxacyclotridecino[2,3,4-gh]- pyrrolizine-2,8(3H)-dione,4,5,6,7,10,12,14,15,- 15a,15b-decahydro-4,6,7-trimethyl-,13- oxide,(4R,6R,7S,15aR,15bR)-