Characterisation of Metal Binding Sites for 8-Azaguanine and 8-Azahypoxanthine Derivatives Synthesis and X-Ray Structural Analysis of Methylmercury(II) and Zinc(II) Complexes

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Abstract
The complexes [(CH3Hg)AGuaH] (1) and [(CH3Hg)2AGua] .cntdot. H2O (2) have been isolated from aqueous 1:1 and 2:1 solutions of CH3HgOH and 8-azaguanine (AGuaH2) at respective pH values of 5 and 9. Only one CH3Hg+ complex of 8-azahypoxanthine (AHxH2), namely [(CH3Hg)2AHx] (3), could be isolated under analogous conditions. X-ray structural analyses established N1 and N9 as metal binding sites in 3 and N9 as the coordination position in [Zn(H2O)4(AHxH)2] (4). With 8-aza-9-benzylhypoxanthine (9-BzAHxH) only one CH3Hg+ complex [(CH3Hg)9-BzAHx] (5) could be isolated in the pH range 2-10. N1 was established by X-ray structural analysis as the binding site. The relevance of these findings to an understanding of ligand behaviour of the antineoplastic agent 8-azaguanine is discussed.