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The synthesis of (Dien)Pt(PMEA-N7), where Dien = diethylenetriamine and PMEA 2-  = dianion of 9-[2-(phosphonomethoxy)ethyl]adenine, is described. No useful biological activity could be discovered for this complex which is in contrast to the known antiviral properties of PMEA itself. The acidity constants of the twofold protonated H 2 [(Dien)Pt(PMEA-N7)] 2+  complex were determined (UV spectrophotometry and potentiometric pH titration): The release of the proton from the -P(O) 2 (OH) -  group is only slightly affected by the N7-coordinated (Dien)Pt 2+  unit, whereas the acidity of the (N1)H +  site is strongly enhanced. The stability constants of the M[(Dien)Pt(PMEA-N7)] 2+  complexes with the metal ions M 2+  = Mg 2+ , Ca 2+ , Mn 2+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ , and Cd 2+  were measured by potentiometric pH titrations in aqueous solution at 25 °C and I = 0.1 M (NaNO 3 ). Application of previously determined straightline plots of log K M(R-PO3)  M  versus K H(R-PO3)  H  for simple phosph(on)ate ligands, R-PO 3  2-  where R represents a non-inhibiting residue without an affinity for metal ions, proves that the primary binding site of the complex-ligand, (Dien)Pt(PMEA-N7), with all the metal ions studied is the phosphonate group; in most instances the expected stability is actually reduced by about 0.4 log units due to the N7-bound (Dien)Pt 2+  unit. Only for the Cu[(Dien)Pt(PMEA-N7)] 2+  and the Zn[(Dien)Pt(PMEA-N7)] 2+  systems the formation of some 5-membered chelates involving the ether oxygen atom of the -CH 2 -O-CH 2 -PO 3  2-  residue could be detected; the formation degrees are 52 ± 9% and 32 ± 14%, respectively. The metal ion-binding properties of (Dien)Pt(PMEA-N7) differ considerably from those of PMEA 2- , yet they are relatively similar to those of pyrimidine-nucleoside 5'-monophosphates. The structures of the various complex species in solution are discussed and compared.

zeitschrift für naturforschung b

Properties of the Ternary (Dien)Pt(PMEA-N7) Complex Containing Diethylenetriamine (Dien) and the Antiviral 9-[2-(Phosphonomethoxy)ethyl]adenine (PMEA). Synthesis, Biological Screening, Acid-Base Behaviour, and Metal Ion-Binding in Aqueous Solution