A simple and fast-response fluorescent probe for hypochlorite in living cells Ruixue Ji, Kun Qin, Aikun Liu, Yan Zhu, Yanqing Ge ⇑ School of Chemistry and Pharmaceutical Engineering, Taishan Medical University, Taian, Shandong 271016, PR China article info Article history: Received 13 March 2018 Revised 1 May 2018 Accepted 12 May 2018 Available online xxxx Keywords: Pyrido[1,2-a]benzimidazole Hydrazone Bioimaging Fluorescent probe Hypochlorite abstract A novel fluorophore pyrido[1,2-a]benzimidazole was synthesized and used as a fluorescent probe for hypochlorite based on the oxidation of hydrazine to carboxyl group. The detection limit was measured to be as low as 7.0 nM. The probe can realize fast-detection for hypochlorite within 60 s. Furthermore, it could be used for imaging in living cells. Ó 2018 Elsevier Ltd. All rights reserved. Introduction Hypochlorite anion (ClO À ), as one of the important reactive oxy- gen species (ROS), plays an essential role in many biological pro- cesses. 1–3 Endogenous ClO À which is formed from the reaction between chloride ions and hydrogen peroxide by the catalysis of enzyme myeloperoxidase is essential to life and has important antibacterial properties. 4 However, abnormal level of ClO À can cause some diseases such as atherosclerosis, arthritis, kidney dis- ease, and cancer. 5–10 Therefore, accurate detection of ClO À in living cells and organisms has become important for us to understand its role in biology. To date, a number of fluorescent probes have been reported for specific detection of ClO À . However, they are still restricted to the limited fluorophores such as coumarin, 11–14 BODIPY, 15–18 rho- damine 19–21 and cyanine. 22–25 Therefore, it is a great challenge to search for novel fluorophores with superior properties. Previously, we successfully synthesized pyrido[1,2-a]benzimi- dazoles (PBI) via a tandem reaction. 26 The compounds were found to have good fluorescence properties such as high fluorescence quantum yield and used as a donor to construct FRET-based ratio- metric probe for identifying Cu 2+ and Hg 2+ . 27,28 In order to extend the application of the new fluorescence, herein, we designed and synthesized a simple PBI-based probe bearing hydrazone moiety to detect ClO À . The mechanism was based on the oxidation reac- tion of C@N by hypochlorite. Experimental section Materials and equipments 1 H NMR spectra were measured on a Bruker Avance 400 (400 MHz) spectrometer (DMSO d 6 as solvent and tetramethylsilane (TMS) as an internal standard). HRMS spectra were recorded on a Q-TOF6510 spectrograph (Agilent). UV–vis spectra and FL spectra were recorded on a U-3900 UV–Vis spectrometer (Hitachi) and RF-5301PC luminescence spectrophotometer (Shimadzu) at room temperature, respectively. All reagents and solvents were pur- chased from commercial sources and used without further purifi- cation. Deionized water was used throughout the process of absorption and fluorescence determination. Cell culture and imaging Glioma cells were cultured in RPMI-1640 containing 10% fetal bovine serum at 37 °C in a 5% CO 2 /95% air incubator. For living cells imaging experiments, the growth medium was removed and replaced with RPMI-1640 without FBS. The cells were treated and incubated with 2 lM of PBI-HClO at 37 °C under 5% CO 2 for 1 h. The cells were washed three times with PBS and then cell images were obtained via a confocal microscope from Radiance 2100 (Bio-Rad) at excitation of 405 nm. https://doi.org/10.1016/j.tetlet.2018.05.027 0040-4039/Ó 2018 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: geyanqing2016@126.com (Y. Ge). Tetrahedron Letters xxx (2018) xxx–xxx Contents lists available at ScienceDirect Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet Please cite this article in press as: Ji R., et al. Tetrahedron Lett. (2018), https://doi.org/10.1016/j.tetlet.2018.05.027