Design, Synthesis And Properties Of Reversible Photoswitchable Deoxynucleoside

Light is a convenient and powerful trigger to control the reactivity of biomolecules. Complex andcompartimentalized environments like cells benefit not only from the noninvasive and noninterferingnature of light, but also from its spatial and temporal resolution. The artificial control of DNA structure andfunction is an attractive field in chemical and synthetic biology. The strategy for the incorporation oflight-responsive units into DNA has become a urgent and awesome task. So, the subject which design andsynthesis of novel photochromic nucleosides compounds should never be neglected.The novel purine-scafflod photochromic deoxynucleoside compounds dA-1and dA-2, withdiarylethenes as light-responsive units and carbon-carbon triple bond as bridge, was devised andsynthetized. Through irradiation with365nm, the absorption spectra of dA-1in different solventenvironments were conducted, but there was no obvious absorption peak which appeared in the visiblerange. Therefore, some improvement on photochromic units were carried on. dA-2, withoctafluorocyclopentene diarylethenes as photochromic unit was designed and synthesized. Throughillumination with365nm, the initially colorless solutions of compound dA-2displayed a strong coloration,which is characteristic for diarylethenes that undergo ring closure. Irradiation with UV-light triggered theemergence of a broad absorption band in the visible range, with dA-2having its maximum at615nm. After5min, the photo-induced isomerization of dA-2reached a plateau. The color rapidly fades upon irradiationwith visible light-due to cycloreversion-demonstrating that compound dA-2are fully functionaldiarylethenes. Cycling between the opened and closed form was performed by alternating illumination with365nm (UV-handheld lamp) and visible light. The result testifies that the photoisomerization is reversibleand can be repeated several times by alternating illumination with365nm (UV-handheld lamp) and visiblelight. The result indicats photochromic performance of compound dA-2is perfect. In addition to light, thecycloreversion of diarylethenes can be triggered thermally. We therefore tested the thermal stability ofclosed-ring isomers and monitored the absorbance changes at different temperatures. The result revealsclosed isomers of dA-2is stable. Because deoxyribonucleoside is the basic component of DNA, theincorporation of dA-2into DNA is expected to synthetize photochromic nucleotide. To provide new waysto solve scientific problems that torment everyone. The development of fluorescent probes are closely related to a large number of practical problems inlife science and clinical medicine. Nucleosides with excellent fluorescence could be used to determine thenucleic acid sequence, detect pathogens and analyze the gene expression so as to play a huge role indiagnosis, pathogenesis of the genetic diseases. Therefore, finding carefully nucleoside-based fluorometricprobe and the research of their ion recognition performance in organisms have important theoreticalmeaning and pratical value. So far, studies on this area are seldom available. It is a very important task tostudy the nucleoside-based fluorescent probes which own novel structure and outstanding ion recognitionperformance.In the second part, adenosine as starting material, we introduced three groups complexing with ionsinto pruine nucleoside ring, then synthesized purine nucleoside compounds L1-L3with novel structure. Ionrecognition research will be conducted in physiological conditions via fluorescence spectra to obtainnucleoside based fluorescent probe L1with highly efficient performance. Therefore, we researched into theproperties of probe L1. The fluorescence titration experiment of L1with Pd2+ions was performed at roomtemperature in aqueous Tris-HCl buffer (10%DMSO, v/v, pH=7.3). With the increase of Pd2+concentration, the intensities of the fluorescence of L1decreased progressively. The competitionexperiment was implemented in the same circumstances, and the results of experiment embodied that thePd2+-induced fluorescence was unaffected. We used S2-titrations of L1-Pd2+systems to check thecoordination between Pd2+and L1. When an excess amount of S2-was added to mixed solutions of L1-Pd2+,the fluorescence gradually recovered owing to decoordination of Pd2+. It suggested the quenching offluorescence was apparently ascribed to the coordination of the DPA (N,N-bis(2-pyridylmethyl)amine)chelator to Pd2+ion. Apparently, L1can function as a sensor for selective dectection of Pd2+. We thenproceeded to the1H NMR titration experiments and ESI mass spectra. The coordination between Pd2+andthe DPA moiety of L1was supported by these chemical shifts, and the stoichiometry of the complex was1:1. The fluorescence intensities of L1is linearly proportional to the concentration of Pd2+ions. Thedetection limit of the sensor for Pd2+ions is estimated to be6.47×10-7M, which means that L1can beused for Pd-polluted analysis in drug according to the WHO specified threshold limit for palladium contentin drug chemicals [4.7×10-5M (5ppm) to9.4×10-5M (10ppm)]. To the best of our knowledge, this isthe first example of a purine nucleoside-based fluorometric probe for Pd2+that demonstrated significant fluorescent quenching. Based on the systemetic research, we expect to obtain the methods that can tune theproperties of recognition of fluorescent probes based on nucleoside for ions. It will be useful and providescientific data for the extensive research and practical application of fluorescent probes.The structure of products were characterized and analysed through1H-NMR,13C-NMR, HRMS.It will provide a novel way for photochromic deoxyribonucleoside and we attempt to provide a surveywith photochromic deoxyribonucleoside. Furthermore, L1is promising to be a potential fluorescent probefor the detection of residual palladium species in environmental and chemical settings. We anticipate thatthe design strategy presented here will help to provide valuable insight in the design of fluorescent sensorsderived from purine nucleoside scaffolds, and our research can broaden applicable approach to exploitingprobes for a wide variety of metal ions.