Akuammilan-17-oicacid, 19,20-epoxy-1,2,19,20-tetrahydro-11-methoxy-10-(17-methoxy-10,17-dioxo-2,4(10H)-cyclo-3,4-secoakuammilan-11-yl)-1-methyl-,methyl ester, (2b,19R,20a)-