Synthesis,Photophysical Properties And Biological Activities Of Sulfur-containing Five-membered Heterocyclic Compounds

In chemical biology research and medical diagnosis,fluorescence imaging has emerged as an important means to monitor and track targets.Various fluorescent molecules have been used as selective bioimaging tools.The protein tyrosine phosphatases（PTPs）represent a large family of enzymes regulating the homeostasis of protein tyrosine phosphorylation,malfunctions in PTP activity are linked to various disease.As one member of PTPs,Src homology-2 domain-containing protein tyrosine phosphatase 1（SHP1）is mainly restricted to hematopoietic and epithelial cells and is widely accepted as a node for cell signaling pathway cascades.The development of efficient methods for rapidly tracing and inhibiting the SHP1 activity in complex biological systems is of considerable significance for advancing the integration of diagnosis and treatment of the related disease.The 1,3,4-thiadiazole core represents an important structure skeleton,which is not only a class of compounds with obvious conjugation effect and aromatic properties,but also often be used as drug intermediates to synthesize drugs with bactericidal and anticancer activities.With this aim,based on the reported SHP1 inhibitors,we designed and synthesized five 2-phenyl-1,3,4-thiadiazole derivatives.The photophysical properties and inhibitory activities of these derivatives against SHP1 were thoroughly studied from the theoretical simulation and experimental aspects.Compound 9 exhibited a larger quantum yield（Φ=0.95）than the other molecules because of the smaller geometric relaxation and reorganization energy of the excited state,which was consistent with the results from the fluorescence experiments in organic solvents.In addition,compound 9 showed a selective fluorescence response for SHP1 activity（P=0.007）and low cytotoxicity in He La cells.Lastly,it indicated the potential application in two-photon cell fluorescence imaging according to the calculated excellent two-photon absorption properties.The preliminary discovery of compound 9 realized the combination of SHP1 inhibitory activity(IC₅₀=51.09±7.06μM)and fluorescence visualization at the enzyme molecular level.Although active compounds with fluorescent properties have been identified,their effect in cell imaging has not been further evaluated due to limitations in experimental design.To further improve the fluorescence properties of the compounds,the optical properties and biological activities of more molecules were evaluated in consideration of the application of integration of diagnosis and treatment.Herein,a series of fluorescent molecules with thiadiazole,or thiazole,or benzothiazole cores were designed and synthesized to develop more excellent bio-imaging molecules.We found that compound 21 with conjugate expansion by alkynyl and benzo groups and with amine group substitution in para-position was the most excellent fluorescent molecule among all the investigated compounds（Φ=0.426）.Although compound 21 had obvious ACQ effect in DMSO-H₂O mixed solvent systems,it had stronger fluorescence intensity in moderate and high polarity solvents.Furthermore,cell experiments illustrated that compound 21 was low cytotoxicity and exhibited strong blue and bright green fluorescence by confocal cell imaging excited at 405 nm and 488 nm.In conclusion,some fluorescent compounds containing sulfur five-membered heterocyclic rings were found,and some of the compounds showed inhibitory activity against SHP1,which provided design ideas for the discovery of excellent fluorescence visualization active molecules.