The Redox Properties of Bleomycin and Tallysomycin and a Series of Their Metalloderivatives

D-c polarographic and cyclic voltammetric studies on bleomycin A2 (BLM-A2), tallysomycin A (TLM-A), a series of their metalloderivatives, and four of their components have been conducted. The antibiotics exhibit two reduction processes. The first, at −1.22V, has been assigned to the two electron reduction of the 4-amino pyrimidine moiety of the drugs. A second multielectron reduction process appears to be associated with the bithiazole portion of the antibiotics. The first polarographic wave, due to the pyrimidine moiety, is sensitive to metal binding phenomena. The binding of Fe(II), Co(II, III), Ni(II), and Zn(II) to the antibiotics, causes this wave to disappear from the polarogram of the metalloderivatives. Thus, for these metal ions the pyrimidine moieties of the drugs appear to be metal ligating sites. The involvement of this group in metal ligation in the case of Fe(III) is highly dependent on the mode of preparation of the complex, and Fe(III) complexes containing both bound and unbound pyrimidine residues are possible. The impact of the electrochemical results on the proposed mechanism of action of the pharmaceuticals is also discussed.