Abstract
The stability constants of the 1 : 1 complexes formed between Mg2+ and the anions of the N1, N3, and N7 deaza derivatives of 9-[2-(phosphonomethoxy)ethyl]adenine (PA2–), i.e., of Mg(H;PA)+ and Mg(PA), were determined by potentiometric pH titration in aqueous solution (25 °C; I=0.1 M, NaNO3) and compared with previous results [Sigel H, et al. (1992) Helv Chim Acta 75 : 2634–2656], obtained under the same conditions, for the corresponding complexes of 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA2–) and (phosphonomethoxy)ethane (PME2–). Based on the analysis of a microconstant scheme it is concluded that in the monoprotonated complexes, Mg(H;PA)+, Mg2+ is coordinated to a significant part at the nucleobase, H+ being at the phosphonate group. By making use of log K Mg Mg(R-PO3) versus pK H H(R-PO3) straight-line plots (also obtained previously; see above) for simple phosphonates and phosphate monoesters, it is shown that all the Mg(PA) complexes, including those with PMEA2– and PME2–, are more stable than expected on the basis of the basicity of the ―PO2– 3 group. This proves that, to some extent, five-membered chelates, Mg(PA)cl/O, involving the ether oxygen of the ―CH2―O―CH2―PO2– 3 chain are formed; their formation degree amounts to about 30–40% in equilibrium with the isomer having only a phosphonate-Mg2+ coordination. In the case of Mg(1-deaza-PMEA), probably a further isomer occurs in which also N3 of the nucleobase participates. The different properties between the Mg(PA) species and the Mg(AMP) complex are discussed.
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Received: 26 January 1998 / Accepted: 19 May 1998
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Blindauer, C., Holý, A., Dvořáková, H. et al. Magnesium complexes of the antiviral 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA) and of its 1-, 3-, and 7-deaza analogues in aqueous solution. JBIC 3, 423–433 (1998). https://doi.org/10.1007/s007750050252
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DOI: https://doi.org/10.1007/s007750050252