(1S,2R,4S,6R)-6-((3aR,4S,6aR,8S,10aR)-8-Acetoxy-4-methyl-3,5-dioxo-decahydro-2-oxa-cyclopenta[d]naphthalen-4-yl)-5-oxo-bicyclo[2.2.1]heptane-2-carboxylic acid