The binding ability of the antitumor compound 7-oxabicyclo-[2.2.1]hept-5-ene-2,3-dicarboxylic acid (OHDA) (I) to essential metal ions was studied potentiometrically at 37?and 150 mmol譫m-3 NaCl. Compared to other dicarboxylic acids, OHDA complexes show extra stability implying the binding of the epoxy O atom to metal ions. The coordination of the epoxy O donor was proved by X-ray crystal diffraction measurements of metal2+-OHDA complexes. Speciation studies illustrate that at pH 6-8, the dominant complex species is Zn2+-OHDA, but at low OHDA concentration (10-4-10-7 mol譫m-3), the Mn2+-OHDA complex species shares the predominant position with Zn2+-OHDA in the complex system. This fact may be related to the antitumor activity of some ligand drug mols. by disturbing normal distribution and metabolism of essential metal ions.

Key words: ANTICARCINOGEN, ZINC COMPLEX, IRON COMPLEX, COPPER COMPLEX, BICYCLOHEPTENE P, OXYGEN HETEROCYCLICS, CALCIUM COMPLEX, HYDRIDO COMPLEX, MAGNESIUM COMPLEX, ALUMINIUM COMPLEX