A small series of five novel berberine derivatives was synthesized by the Cu-catalyzed click reaction of 9-propargyladenine with 9-O-(azidoalkyl)berberine derivatives. The association of the resulting berberine–adenine conjugates with representative quadruplex-forming oligonucleotides 22AG dA(G₃TTA)₃G₃ and a2 d(ACAG₄TGTG₄)₂ was examined with photometric and fluorimetric titrations, thermal DNA denaturation analysis, and CD spectroscopy. The results from the spectrometric titrations indicated the formation of 2:1 or 1:1 complexes (ligand:G4-DNA) with log K_b values of 10–11 (2:1) and 5–6 (1:1), which are typical for berberine derivatives. Notably, a clear relationship between the binding affinity of the ligands with the length of the alkyl linker chain, n, was not observed. However, depending on the structure, the ligands exhibited different effects when bound to the G4-DNA, such as fluorescent light-up effects and formation of ICD bands, which are mostly pronounced with a linker length of n = 4 (with a2) and n = 5 (with 22AG), thus indicating that each ligand–G4-DNA complex has a specific structure with respect to relative alignment and conformational flexibility of the ligand in the binding site. It was shown exemplarily with one representative ligand from the series that such berberine–adenine conjugates exhibit a selective binding, specifically a selectivity to quadruplex DNA in competition with duplex DNA, and a preferential thermal stabilization of the G4-DNA forms 22AG and KRAS. Notably, the experimental data do not provide evidence for a significant effect of the adenine unit on the binding affinity of the ligands, for example, by additional association with the loops, presumably because the adenine residue is sterically shielded by the neighboring triazole unit.

中文翻译：

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四链体 DNA 结合 9-O-取代小檗碱衍生物的合成和研究


通过 9-炔丙腺嘌呤与 9- O- (叠氮烷基)小檗碱衍生物的铜催化点击反应合成了五种新型小檗碱衍生物。通过光度和荧光滴定、热 DNA 变性分析和 CD 检查所得小檗碱-腺嘌呤缀合物与代表性四联体形成寡核苷酸22AG dA(G ₃ TTA) ₃ G ₃和a2 d(ACAG ₄ TGTG ₄ ) ₂的关联。光谱学。光谱滴定结果表明形成了 2:1 或 1:1 复合物（配体：G4-DNA），log K _b值为 10-11 (2:1) 和 5-6 (1:1)，其中是小檗碱衍生物的典型。值得注意的是，没有观察到配体的结合亲和力与烷基连接链长度n之间的明确关系。然而，根据结构的不同，配体与 G4-DNA 结合时表现出不同的效果，例如荧光发光效果和 ICD 带的形成，这在接头长度为n = 4（ a2 ）和n = 5（ 22AG ），因此表明每个配体-G4-DNA复合物在结合位点配体的相对排列和构象灵活性方面具有特定的结构。该系列中的一个代表性配体示例性地表明，此类小檗碱-腺嘌呤缀合物表现出选择性结合，特别是与双链体 DNA 竞争时对四链体 DNA 的选择性，以及 G4-DNA 形式22AG和KRAS的优先热稳定性。 值得注意的是，实验数据没有提供腺嘌呤单元对配体的结合亲和力的显着影响的证据，例如通过与环的额外缔合，大概是因为腺嘌呤残基被邻近的三唑单元空间屏蔽。