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Development of natural product derivatives for the fluorimetric DNA detection in cells

Subject Area Organic Molecular Chemistry - Synthesis and Characterisation
Term from 2020 to 2026
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 453712865
 
Final Report Year 2024

Final Report Abstract

This project dealt with the development of fluorescent probes based on natural products for the detection of nucleic acids. In particular, the underlying structures of natural products should support the required biocompatibility for DNA detection in cells. For this purpose, the basic structures of protoberberine and β-carboline alkaloids were modified in such a way that the resulting derivatives have a very low fluorescence intensity, which increases characteristically when binding to DNA, thus enabling the targeted fluorimetric analysis. Berberine and harmane scaffolds were functionalized at different positions, and the most promising derivatives of these series were further investigated as probes for fluorimetric cell analysis. Specifically, aryl-substituted derivatives showed low fluorescence quantum yields because of a deactivation of the excited state by rotation around the biaryl axis. In turn, the emission intensity increased upon complexation with DNA, mostly pronounced with methoxysubstituted derivatives. The latter enabled the staining of nucleoli in eukaryotic cells. Notably, one berberine derivative exhibited a fluorescence light-up effect exclusively in the nucleus in fixed cells, so that it may be used as indicator dye for cell death. In contrast, an amino-substituted berberine derivative showed pH- and DNA-dependent fluorescence. Namely, its low emission intensity did not increase upon association with DNA at neutral conditions, whereas at pH 5 a fluorescence light-up effect resulted from association with quadruplex DNA. Series of the coralyn-related quinolizinium ions were also investigated as multifunctional fluorescent probes. A dimethylamino-substituted derivative was identified that is nonfluorescent in buffer solution, but exhibited different light-up effects upon association with duplex DNA, quadruplex DNA, RNA, and BSA, which enabled the fluorimetric differentiation between these analytes. Hence, this dye was employed for the analysis of the cell nucleus by epifluorescence and fluorescence lifetime imaging microscopy (FLIM). Likewise, the characteristic emission properties of an aminoquinolizinium were released by the reaction of the non-fluorescent nitro-substituted precursor with nitroreductase. This fluorogenic reaction in the enzyme binding site was exemplarily utilized for the fluorimetric detection of reductase activity in E. coli and may thus be used to determine the hypoxia status of cells. Steady-state and time-resolved photophysical studies of hydroxy-substituted harmane derivatives showed that these compounds can be used for the fluorimetric monitoring of probe-water interactions. However, the detailed analysis of water dynamics, in particular in the microenvironment of DNA, cannot be performed with these dyes as they do not provide the required delicate balance between ground and excited-state acidity, photophysical properties, and DNA binding.

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