Synthesis And Properties Of Pyrimidine Fluorescent Nucleoside Analogs

Fluorescence recognition has been widely applied in the field of nucleic acids in recent years.The reliability and responsiveness of fluorescence spectroscopy is fundamentally dependent on the characteristics of fluorescent probes.Hence the preparation of nucleoside fluorescent probe with low toxicity,high quantum yield and good sensitivity is highly concerned.Nucleoside,the fundmental building block of DNA and RNA,can serve as good framework for constructing the nucleoside fluorescent probe.Fluorescent nucleoside analogues are not only highly emissive but also sensitive to changes in microenvironment.More importantly,they have good biocompatibility than other fluorescent probes.While incorporated into oligonucleotides,fluorescence nucleoside analogs can make normal biological function with similar structure to natural nucleosides.In this thesis,introducing the electronegative nitrogen at the 6-position,aromatic ring system was expected to enhance “push-pull” interaction,with different substituents,thiophene,naphthalene,benzothiophene and benzofuran in the 5-position of uracil.We synthesized a series of fluorescent uridine analogues with maximum emission in visible region.5-Aryl-6-aza uracil was prepared in two steps using arylketone and semicarbazide hydrochloride as the raw materials.Through reaction between ?-D-ribofuranose-1-acetate 2,3,5-tribenzoate and the modified base,a series of fluorescent uridine analogues were achieved after in situ alcoholysis procedure.The major compounds were characterized by 1H NMR,13 C NMR and MS.The UV absorption and fluorescent property of these fluorescent uridine analogues were investigated in various polarity,pH and viscosity conditions.In addition,the recognition effect of 5-(4-fluorophenyl)-6-aza uridine 3c for different metal cations was also carried out.Emitted in the range from 419 to 464 nm,four aryl-modified uridine analogues exhibited good sensitivity toward polarity and pH.The electron-donating substituent for benzene promoted the bathochromic shift of the emission wavelength for uridine analogues.Compounds 3a,3c and 3d showed good sensitivity to viscosity.Compound 3c exhibited the quantum yield up to 0.81 in water and good selectivity toward Pd2+ in the range of 5.0×10-7 mol/L~5.0×10-6 mol/L.The detection limit was estimated to be 2.0×10-7 mol/L.With the increasement in the polarity of solvent,the emission of 5-(thiophene-3-yl)-6-aza-uridine 6 showed remarkable bathochromic shift effect and emission maximum at 432 nm in water.In contrast to other aryl-modified uridine analogues,better correlation with ET(30)of 6 indicated heteroatom effect of stronger susceptibility to polarity.Be sensitive to pH and viscosity change,compound 6 was not influenced by natural nucleosides.It also displayed significantly improved sensitivity of viscosity with hypochromatic shift effect and decreased quantum efficiency compared with 5-(thiophene-2-yl)-6-aza-uridine.Extending the conjugated electron-poor/electron-rich biaryl system,uridine analogues with benzoheterocycle showed a significant bathochromic shift(?em = 470~480 nm).9b and 9c were sensitive to solvent polarity,especially the increased fluorescence quantum yield of 9c with the decrease of polarity(? = 0.04 in water,? = 0.78 in dioxane).The fluorescence intensity of 9b and 9c showed good correlation with pH and viscosity.9a only showed sensibility to pH in absence of hetero atoms in extending armonic ring structure.Generally,all the eight fluorescent nucleoside analogs could act as flurescence probes,with anti-interference ability to natural nucleosides and sensibility to changes in microenvironment.