Design And Synthesis Of Near-infrared Fluorescein Derivatives

Fluorophore is a important part of fluorescent probe, it acts as fluorescent signal in the process of identifying the ligand analyte. Thus, the photochemical properties of the fluorophore determines the fluorescent molecular probe’s spectral properties. There is no doubt that the importance of fluorore’s role. To choose appropriate fluorophore for a fluorescent molecular probe, We must consider its fluorescence quantum yield, the maximum absorption and emission wavelengths, light stability, Stocks displacement, water-solubility and lipid solubility, biological toxicity, cell penetrability and so on. Fluorescein is widely used in the design of fluorescent molecular probes due to its excellent spectral properties. Base on its two quinonoid tautomer and lactone tautomer, fluorescein can balance between ring-opening form and ring-closing form. In the neutral or acidic environment, fluorescein dyes are in the presence of lactone structure, them have almost no UV absorption or fluorescent emission in the visible region. In the basic environment, fluorescein dyes are in the presence of quinone structure, them have a strong characteristic absorption and fluorescent emission, which are excellent switch-type fluorophores.Fluorescein without structural modification, its maximum absorption and fluorescent emission wavelength is490nm and525nm respectively. Fluorescent probes design and synthesis by this kind of fluorescein, their maximum absorption and fluorescent emission wavelength less than650nm largely. If them applied in biological cells, the biological matrix or intracellular impurities may have absorption or fluorescent emission in this wavelength region, and light scattering will usually have a serious background interference, which may affect the accuracy of probe seriously. Besides, using short-wavelength excitation light irradiate biological samples may have great damage.In this dissertation, we attempted to synthesis four fluorescein derivatives, four important intermediates and one fluorescein derivative were synthesized. Using2,3,3-Trimethylindolenine as raw material, by introducing a methyl group and double bond shifting,1,3,3-Trimethyl-2-methyleneindoline was gained. Than it reacted to Vilsmeier reagent and malondialdehyde bis(phenylimine) monohydrochloride respectively, indolealdehyde intermediate M1and M2were synthesized; Using resorcinol and phthalic anhydride as raw materials, by Friedel-Crafts acylation and concentrated sulfuric acid condensation, fluorescein analogue M3was synthesized; Using fluorescein as the raw material, by Reimer-Tiemann reaction, fluorescein-monoaldehyde intermediate M4was synthesized. The hexaheterocyclic construction conditions of fluorescein category M3was researched in depth, found its best synthesis conditions. Also the catalysts to the synthesis of fluorescein-aldehyde intermediates M4was studied, and found the two best catalysts for the reaction. Compound L3and intermediates were characterized by ’H-NMR and MS, The fluorescence and UV absorption of Compound L3was studied preliminarily. Compared to fluorescein, the fluorescent of compound L3was red-shifted, it can be an excellent fluorophore.