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 (1D6PP), 7‐deaza‐6PP (7D6PP) and 1,7‐dideaza‐6PP (1,7D6PP) 2′‐deoxyribonucleosides, respectively, were investigated towards their ability to form metal‐mediated base pairs in the presence of AgI. In 6PP and 7D6PP, the AgI 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 1D6PP and 1,7D6PP, so that in 1D6PP an AgI 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 AgI‐binding properties. To determine the thermal and structural duplex stabilities in the absence or presence of AgI, 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. The artificial nucleobase 6‐pyrazolylpurine and its 1‐deaza‐, 7‐deaza‐ and 1,7‐dideaza derivatives were investigated with respect to their silver(I)‐binding abilities in silver(I)‐mediated base pairs in DNA. A comparison of the experimental data indicates that the N1 position of the purine derivative is the preferred silver(I)‐binding site, that is, that silver(I)‐mediated base pairing involves the Watson–Crick edge.