Benzothiazole-substituted Cryptolepine Derivatives As G-quadruplex DNA And PH Fluorescent Probes

Recent years, small molecule fluorescent probes have become an extremely important tool for the life sciences, which have been widely used in nucleic acid quantitative analysis and living cells fluorescence imaging for its simple operation, high sensitivity and good selectivity. G-quadruplexes are unique nucleic acid structures formed by G-rich DNA sequences. In2013it was shown that G-quadruplexes exist in the human genome related with the cancer development and metastasis. Scientists find that fluorescent probe is one of the ideal mean to identify, detect and cell image of G-quadruplexes.Cryptolepine, extracted from a shrub plant in West Africa, is an important alkaloid in nature. Its11-aliphatic amino-substituted derivatives can bind well with the G-quadruplex, however they have no fluorescence responce in the present of G-quadruplexes. Thiazole orange (TO) is an excellent nucleic acid fluorescence probe; it has a high fluorescence quantum yield in the present of nucleic acid. Howerver it has not selectivity to G-quadruplex. Cryptolepine shares the quinoline fragment with TO. In the preliminary study, our group conjugated the benzothiazole fragment of TO to cryptolepine scaffold and formed a novel fluorescent probe CYTO. Studies showed that the fluorescence intensity of CYTO was enhanced remarkably upon binding to human telomere G-quadruplex DNA. However, it has poor water solubility and selectivity to G-quadruplexes.In the thesis, we introduced different side chains in the benzothiazole group of CYTO and synthesized a series of new compounds1-13in order to improve their selectivity, water-solubility and sensitivity as G-quadruplex fluorescent probes.The main works are shown as follow:(1) A review on the research and development of some G-quadruplex structures.(2) The rational design and synthesis of a series of benzothiazole-substituted cryptolepine derivatives.(3) The fluorescence properties of derivatives as G-quadruplex fluorescent probe were investigated.(4) The effects of the compounds to G-quadruplex structure were investigated by CD spectroscopy.(5) The binding mode of derivatives with G-quadruplex were investigated by molecular docking,(6) The application of derivatives as pH fluorescent probes were investigated by UV spectra and fluorescence spectra.The results show that:(1) Derivatives binded with G-quadruplex by external stacking, the main force are π-π and electrostatic interaction.(2) Benzofuran-quinoline derivatives showed stronger binding ability than indole-quinoline derivatives with stronger fluorescence intensity when binded with G-quadruplex.(3) The introduction of side chains can improve the binding capacity of derivatives to G4; and the binding capacity of derivatives with cyclic amine substituted side chain is stronger than the derivatives with aliphatic amine side chain, accompanied by stronger fluorescence intensity.(5) Derivatives can promote the formation of anti-parallel G-quadruplex structure.(6) Benzofuran derivatives have enhanced fluorescence remarkably with the decrease of pH value, and had good linear relationship in the range of pH from2to5.