57629-50-2 ISOBRUCEIN A NSC279503 Picras-3-en-21-oic acid, 13,20-epoxy-1,11,12-trihydroxy-15-(3-methyl-1-oxobutoxy)-2,16-dioxo-, methyl ester, (1.beta.,11.beta.,12.alpha.,15.beta.)- Picras-4-en-21-oic acid, 13,20-epoxy-1,11,12-trihydroxy-15-(3-methyl-1-oxobutoxy)-2,16-dioxo-, methyl ester