Fig. 1

The origin, evolvement and molecular formula of norcantharidin (NCTD). Mylabris, also known as Spanish fly, is a traditional Chinese medicine. Cantharidin (CTD), a 7-oxabicyclo [2.2.1] heptane-2, 3-dicarboxylic acid derivative, a natural toxin and the active ingredient with antitumor properties extracted from a traditional Chinese medicine Mylabris. NCTD (7-oxabicyclo [2.2.1] heptane-2, 3-dicarboxylic anhydride), with a molecular formula of C₈H₈O₄ and formula weight of 168.15 g/mol, is the demethylated analog and the low-cytotoxic derivative of CTD with antitumor properties