Design And Synthesis Of Fluorescent Probes Based On 1,4-dihydropyridine Scaffold For Sensing Reactive Oxygen Species

In the physiological process,the reactive oxygen species(ROS)are constantly produced and consumed to maintain redox balance.ROS,including hydrogen peroxide(H₂O₂),superoxide(O₂.^-),hydroxyl radical(OH.,singlet oxygen()1O₂),hypochlorous acid/hypochlorite(HCl O/Cl O^-),hypobromous acid/hypbromite(HBr O/Br O^-),peroxynitrite(ONOO^-),and nitric oxide(NO.),play vital roles in physiological processes such as cell signal transduction,neurotransmission,and blood pressure modulation.However,increased production of ROS would induce oxidative stress through the oxidation of biomolecules,such as the proteins,lipids,and DNA,leading to various diseases including cancer,inflammation,cardiovascular diseases,and neurodegenerative diseases.Therefore,the elucidation of the biological functions of ROS becomes an important area of research.However,one of the major obstacles to understand the roles that these species play is the lack of suitable methods for detecting ROS due to their very short lifetimes and the presence of various biomolecules in cells.In recent years,fluorescent probes present the advantages of higher sensitivity,better selectivity,simple manipulation,and less invasiveness compared with other approaches,and have thereby been widely used for the detection of ROS.Coenzyme NAD(P)H plays a vital role in maintaining redox balance by transferring a hydride ion or an electron to the surrounding oxidizing substances.Research has shown that its reactive center is the 1,4-dihydropyridine ring,and 1,4-dihydropyridines therefore have been known as a NAD(P)H model compounds.The 1,4-dihydropyridine ring having the tendency to form aromatic ring,is readily oxidized to pyridine ring structure with the change of its electron density.Based on the Hantzsch containing 1,4-dihydropyridine ring structure as the recognition site for ROS,we have designed and synthetized a series of novel fluorescent probes and the main work is as follows:Following the design of fluorescent probes,we reported herein the design and synthesis of a series of potential ROS probes.It was found that 1,4-dihydropyridine ring in the presence of ROS is rapidly oxidized to the pyridine ring.After the initial screening,the probe 5b-1 was discovered as selective recognition of ONOO^-.To verify the selectivity of 5b-1 for ONOO^-,the fluorescence changes of 5b-1 were examined by addition of various ROS.After 10 min,negligible changes were observed with other ROS while almost a 7-fold enhancement towards ONOO^-.The above experimental results indicate that the probe 5b-1 has good selectivity for ONOO^-and the practical applications of 5b-1 for the detection of ONOO^-in living cells were carried out.The results provide an ideal fluorescent probe for ONOO^-and provide a more broad platform for the application of 1,4-dihydropyridines.