Silver(I) Coordination in Silver(I)‐Mediated Homo Base Pairs of 6‐Pyrazolylpurine in DNA Duplexes Involves the Watson–Crick Edge

DNA duplexes comprising 6‐(1H‐pyrazol‐1‐yl)‐9H‐purine (6PP), 1‐deaza‐6PP ((1D)6PP), 7‐deaza‐6PP ((7D)6PP) and 1,7‐dideaza‐6PP ((1,7D)6PP) 2′‐deoxyribonucleosides, respectively, were investigated towards their ability to form metal‐mediated base pairs in the presence of Ag(I). In 6PP and (7D)6PP, the Ag(I) ion can coordinate to the nucleobase via the endocyclic N1 nitrogen atom, that is, via the Watson–Crick edge. In contrast, this nitrogen atom is not available in (1D)6PP and (1,7D)6PP, so that in (1D)6PP an Ag(I) coordination is only possible via the Hoogsteen edge (N7). Reference duplexes with either adenine:adenine mispairs or canonical adenine:thymine base pairs were used to investigate the impact of the pyrazolyl moiety on the Ag(I)‐binding properties. To determine the thermal and structural duplex stabilities in the absence or presence of Ag(I), all duplexes were examined by UV and circular dichroism spectroscopic studies. These investigations shed light on the question of whether N1‐ or N7‐coordination is preferred in purine‐based metal‐mediated base pairs.