5,6-dimethyl-7-oxabicyclo[2.2.1]heptane-5,6-dicarboxylic acid NSC115503 HSCI1_000263 5′-3′2,3-Dicarboxy-2,3-dimethyl-1,4-epoxycyclohexane exo-1,6-Dicarboxy-endo-1,6-dimethyl-7-oxabicylco[2,2,1]heptane Lopac0_000318 EU-0100318