81608-59-5 Methyl 13,20-epoxy-2,3,11,12,16-pentahydroxy-15-(3-methyl-1-oxobutoxy)picrasan-21-oate Picrasan-21-oic acid, 13,20-epoxy-2,3,11,12,16-pentahydroxy-15-(3-methyl-1-oxobutoxy)-, methyl ester