Firstly, the self-stacking properties of ATP4- and the effects of metal ions and protons on these properties are described. Some examples involving macrochelate formation between phosphate-coordinated metal ions (M2+) and N7 of the adenine residue in MATP2- are discussed, and this is followed by considerations on mixed ligand complexes consisting of ATP4-, M2+, and amino acid anions with side chains that allow either aromatic-ring stacking or hydrophobic interactions with the adenine moiety; this gives rise to selectivity. Next, the properties of diphosphorylated 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA2-; Adefovir), i.e., of PMEApp4-, are compared with those of (2'-deoxy)ATP4- with regard to their metal ion-binding qualities, and in this way it can be explained why PMEApp2- is initially an excellent substrate for nucleic acid polymerases. Of course, after incorporation of the PMEA residue into the growing nucleic acid chain, this is terminated and this is how PMEA exerts its antiviral properties [its bis(pivaloyloxymethyl)ester, Adefovir dipivoxil, was recently approved for use in hepatitis B therapy]. Finally, the change in free energy connected with (macro)chelate formation or intramolecular stacking interactions and the effect of a reduced dielectric constant of the solvent on the stability of complexes and their structures in solution is considered.
Adenosine 5'-triphosphate (ATP4-): Aspects of the coordination chemistry of a multitalented biological substrate
