Reaction of cis and trans isomers of platinum(II) diamminedichloride with purine, adensine and its derivatives in dilute solutions.

Reactions of the cytostatic and antitumour agent, cis-platinum(II) diamminedichloride, and its trans isomer with purine, adenine and its N-9 derivatives were followed spectrophotometrically in dilute aqueous solutions. While the cis isomer formed with all compounds studied complexes with the metal-to-ligand ratios ML, ML2 and M2L, it was found that the trans isomer did not form the complexes ML2 with adenosine and AMP. The values of dissociation constants, reaction rate constants and activation energies of the reactions of the cis and trans isomers with purine, adenine, and its derivatives were in most cases comparable. Lower stability was exhibited only by the complexes of trans-platinum(II) diamminedichloride (trans-Pt(II)) with AMP as well as by its complexes M2L with adenine and adenosine. The ability of cis-platinum(II) diamminedichloride (cis-Pt(II)) to react with two adenine residues can explain the greater tendency of the cis isomer to form intrastrand cross-links in nucleic acids as compared with the trans isomer.