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The association of heteroaromatic ligands with DNA is an important and biologically relevant process, because it may have a strong influence on the function of the nucleic acid. As a result, efficient and selective DNA-targeting ligands are considered as promising lead structures for drugs. In this context, we established the quinolizinium ion as a versatile building block for the design of DNA-binding ligands, with the long-term goal to evaluate and understand the structural parameters that govern the association of cationic hetarenes with DNA. In this account we demonstrate that annelated quinolizinium derivatives are easily available and that their structure and substitution pattern are highly variable. Most notably, the availability of several derivatives with different size and shape enables the assessment of structure–property relationships regarding their DNA-binding properties. It is shown with exemplary case studies that the systematic variation of the ligand structure, along with analysis of the binding parameters, can be employed to analyze the structural requirements of a ligand to bind to different DNA forms, such as triplex, quadruplex and abasic site-containing DNA. 1 Introduction 2 Association of Quinolizinium Derivatives with Double-Stranded DNA 3 Association of Quinolizinium Derivatives with Triplex DNA 4 Association of Quinolizinium Derivatives with Quadruplex DNA 5 Association of Quinolizinium Derivatives with Abasic Positions in DNA 6 Conclusion

Mismatched (non-Watson–Crick) base pairs represent the most common type of DNA damage, as they are permanently formed in living cells due to erroneous insertion, deletion and misincorporation of bases. In vivo, they are readily recognised and repaired by the proteins of the DNA mismatch repair system, which identify the mismatch sites with high efficiency and fidelity. Notably, the last decades have witnessed the development of several chemically diverse families of small organic molecules and metal complexes that selectively bind to mismatched base pairs (and not to fully paired double-stranded DNA), much like the proteins of the mismatch repair system. This review focuses on these DNA mismatch-binding ligands, with an emphasis on their (often unusual) binding modes, as well as on the similarities and differences between the different classes of mismatch binders. Also discussed are the potential bioanalytical and therapeutic applications of mismatch-binding ligands.

An improved preparation of 1,7-dimethylnaphthalene is presented, which is used as a precursor for the synthesis ofdiazoniahexacyclic salts, namely, 4a,14a-diazoniaanthra[1,2-a]anthracene (3) and 13a,16a-diazoniahexaphene (7). The influence of the reaction conditions on the formation of these isomers was investigated. Notably, the selectivity of the reactions depends significantly on the acid employed in the cyclization step. Both compounds exhibit similar absorption and fluorescence emission properties. Compound 3 exhibits a remarkable photopersistence in the solid state and in air-saturated aqueous solutions. However, diazoniahexaphene 7 undergoes rapid photodegradation in solution. X-ray diffraction analysis reveals that compound 3 adopts a helicene structure in the crystalline state.