A new metal-coordinative flavin(2,4,7-trimethylquino left bracket 8,7-g right bracket pteridine-9,11(7H,10H)-dione: (1) which has a phenanthroline-like skeleton within the molecular structure was synthesized. Being different from conventional flavins, the new flavin showed a significant affinity toward metal ions and the absorption spectra were sensitively affected by added metal ions. The spectral patterns were classified into three types, which were assigned respectively to the different coordination structures. It was demonstrated through oxidation of dihydropyridine derivatives, phenylhydrazine, and L-ascorbic acid that complexed metal ions are able to 'activate' 1 as oxidizing agent. The complexes with Zr**4** plus and Fe**3** plus even oxidized alcohols at ambient temperature. Unexpectedly, it was found that tetrahedral coordination metals such as Cd**2** plus , Zn**2** plus , and Co**2** plus frequently give the stable semiquinone radical of 1.
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