Design,Synthesis And Properties Of Nucleoside-Based Fluorescent Photoswitches

Controlling the structure and function of biomolecules in a reversible manner is a fascinating challenge in chemical and synthetic biology.As a convenient and powerful trigger,light is generally noninvasive,offers a high level of spatiotemporal resolution,and is orthogonal toward living systems.Among the variety of artificial photochromic molecules,diarylethene photoswitches have attracted considerable attention due to their versatile and colorful features.Therefore,reversible photocontrol of biological systems by the incorporation of diarylethene photoswitches has become a powerful route to investigate and control the biological processes in vitro and in living cells.In the area of nucleic acids,different molecular photoswitches including azobenzenes,stilbenes,and diarylethenes have been introduced in the ribose moiety,the nucleobase,or the phosphate backbone in native nucleic acids.In recent years,different kinds of diarylethene photoswitches bonded to biomolecules including peptides,nucleobase,nucleosides and DNA,have been developed.By contrast,introducing diarylethene unit into the nucleobase moiety of nucleoside has been less studied.In the context of ongoing projects for the modification of purine nucleoside analogues herein,we will develop the diarylethene photoswitches based on natural deoxyadenosine using Sonogashira-type cross couplings as key steps by linking diarylethene units to the C8 position of deoxyadenosine via an alkynyl group.In aqueous solvents,some of them exhibited good photochromic properties,including obvious change in color upon irradiation with 365 nm,red-shift of the absorption wavelength,good fatigue resistance,thermal stabilities,conversion efficiency,and base pairing properties.They exhibited the following advantages : 1)commercially available of the starting material deoxyadenosine;2)good base pairing property due to the natural deoxyadenosine moiety;3)red-shift obviously owing to the extended conjugated system of the closed-ring species.Diarylethene photoswitches based on natural deoxyadenosine have been synthesized.The strong absorption band of the closed isomers in the visible range suggests a considerable quenching potential of attached fluorescent dyes as it has been shown for other diarylethene-fluorophore conjugates.This could be exploited for conditional resonance energy transfer to reversibly switch fluorescence on and off,a very useful property for bioimaging applications or super-resolution microscopy.But they are no emissive either as opened isomer or closed isomer.A fluorophore that was selected linking to photochromic diarylethenes allows formation of new photoswitches that are highly emissive as open-ring isomers and also the fluorescence was switched on and off with alternate ultraviolet and visible light irradiation.BODIP Y dyes were selected as fluorophore,because of the characteristic of modifying easily and high efficiency of fluorescence.In the second part,deoxyadenosine was utilized as basic scaffold,with BODIP Y dye as fluorophore candidate due to excellent fluorescent properties and diarylethenes as photochromic unit.Firstly,different moieties were synthesized,and then nucleoside-based fluorescent photoswitches DAB-1,DAB-2 was synthesized through the coupling reactions using the alkynyl groups as the main connecting bridges.Effect of environmental factors on the photophysical and chemical properties was evaluated.They were applied to the real-timing monitor ing of micro-environment and bioimaging in living cells.Research results indicate that through irradiation with UV-light,the closed isomer gives rise to fluorescence quenching with undergoing a reversible electrocyclic rearrangement and a fluorescent “Off” state was obtained.Upon illumination of visible light,the close-form can be switched to its opened isomer counterpart.Such conversion restores the fluorescence emission,and a fluorescent “On” state was obtained.Thus,reversible conversion of fluorescent OFF/ON status was realized.The fluorescence of dyes DAB-1,DAB-2 locting in the lysosomes was examined by costaining cells with a commercially available lysosome-specific dye Lyso Tracter Red.The obtained results are useful in the monitoring of micro-environment and bioimaging in lysosome,which played an important role on basic research of development of numerous diseases.Therefore,it will provide scientif ic proof for extensively fundamental research and actual application of functional fluorescent nucleosides in biological recognition,that is essential and highly valuable in terms of academy and application.